Wikipedia - Benutzerbeiträge [de]

Squeaky Dolphin

2014-01-31T09:12:37Z

Someone not using his real name: /* See also */

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]].<ref name=zdnet/> Facebook has since then encrypted the data.<ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation, which was originally shown to an [[NSA]] audience and was made public by the NBC, contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[Five Eyes]]
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-31T09:11:36Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]].<ref name=zdnet/> Facebook has since then encrypted the data.<ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation, which was originally shown to an [[NSA]] audience and was made public by the NBC, contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[Five eyes]]
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-31T09:05:01Z

Someone not using his real name: I'm removing this though because all we know of NSA's involvement in this is that they were given a presentation of the program

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]].<ref name=zdnet/> Facebook has since then encrypted the data.<ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation made public by the NBC contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:10:34Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on the [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]].<ref name=zdnet/> Facebook has since then encrypted the data.<ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation made public by the NBC contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:04:54Z

Someone not using his real name: /* Scope of surveillance */

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on the [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation made public by the NBC contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:04:44Z

Someone not using his real name: /* Scope of surveillance */

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on the [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

The presentation made public by the NBC contains a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:03:36Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on the [[NBC]] on January 27, 2014 based on documents previously leaked by [[Edward Snowden]].<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref> The presentation made public contained a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:02:49Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public on the [[NBC]] on January 27, 2014.<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref> The presentation made public contained a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T20:02:05Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks. The program was first revealed to the general public by [[NBC]] on January 27, 2014.<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref> The presentation made public contained a note saying the program was “Not interested in individuals just broad trends!”. However, "according to other Snowden documents" obtained by NBC, in 2010, "GCHQ exploited unencrypted data from Twitter to identify specific users around the world and target them with propaganda."<ref name=NBCJan14/>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T19:43:10Z

Someone not using his real name: Filling in 3 references using Reflinks

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks.<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>{{cite web|last=Kelion |first=Leo |url=http://www.bbc.co.uk/news/technology-25927844 |title=BBC News - Snowden leaks: GCHQ 'spied on Facebook and YouTube' |publisher=Bbc.co.uk |date=1970-01-01 |accessdate=2014-01-30}}</ref> which has however encrypted its communications since this presentation was made<ref>{{cite web|author=Matt Swider  |url=http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229 |title=YouTube, Facebook data caught up in UK's 'Squeaky Dolphin' spy program | News |publisher=TechRadar |date= |accessdate=2014-01-30}}</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>{{cite web|url=http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/ |title=Splunk and the Squeaky Dolphin: when Big Data goes rogue | PC Pro blog |publisher=Pcpro.co.uk |date=2008-04-15 |accessdate=2014-01-30}}</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T19:41:32Z

Someone not using his real name: /* Scope of surveillance */

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks.<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]],<ref>http://www.bbc.co.uk/news/technology-25927844</ref> which has however encrypted its communications since this presentation was made<ref>http://www.techradar.com/news/internet/web/youtube-facebook-data-caught-up-in-uk-s-squeaky-dolphin-spy-program-1219229</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T19:36:47Z

Someone not using his real name:

'''Squeaky Dolphin''' is a program developed by the [[Government Communications Headquarters]] (GCHQ) to collect and analyze data from [[social media]] networks.<ref name=NBCJan14>{{cite news|url=http://investigations.nbcnews.com/_news/2014/01/27/22469304-snowden-docs-reveal-british-spies-snooped-on-youtube-and-facebook?lite|title=Snowden docs reveal British spies snooped on YouTube and Facebook|date=27 January 2014|publisher=NBC News|author=Richard Esposito, Matthew Cole, Mark Schone, Glenn Greenwald|accessdate=27 January 2014}}</ref>

== Scope of surveillance ==

According to a document of the GCHQ dated August 2012, the program enables broad, [[Real-time data|real-time]] surveillance of the following items:

* [[YouTube]] video views<ref name=zdnet>{{cite web|last=Dignan|first=Larry|title=Snowden's Squeaky Dolphin leak: Brits spy on YouTube, Facebook behavior|url=http://www.zdnet.com/snowdens-squeaky-dolphin-leak-brits-spy-on-youtube-facebook-behavior-7000025641/|publisher=[[ZDNet]]|accessdate=28 January 2014|date=28 January 2014}}</ref><ref name=NBCJan14/>
* The [[Like button]] on [[Facebook]]<ref name=zdnet/><ref name=NBCJan14/>
* [[Blogger (service)|Blogspot/Blogger]] visits<ref name=zdnet/><ref name=NBCJan14/>
* [[Twitter]]<ref>http://www.bbc.co.uk/news/technology-25927844</ref>

The program can be supplemented with commercially available analytic software to determine which videos are popular among residents of specific cities.<ref name=NBCJan14/> The dashboard software chosen was made by [[Splunk]].<ref>http://www.pcpro.co.uk/blogs/2014/01/28/splunk-and-the-squeaky-dolphin-when-big-data-goes-rogue/</ref>

== See also ==
* [[MUSCULAR]] — program for capturing Google and Yahoo private cloud data

==References==
{{Reflist}}

== External links ==
* [http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/snowden_youtube_nbc_document.pdf Slides released by NBC]

{{National Security Agency}}

[[Category:Government Communications Headquarters]]
[[Category:Mass surveillance]]
[[Category:National Security Agency]]
[[Category:Surveillance scandals]]

Squeaky Dolphin

2014-01-30T19:33:06Z

Someone not using his real name: /* Scope of surveillance */

Squeaky Dolphin

2014-01-30T19:18:14Z

Someone not using his real name: /* References */

Squeaky Dolphin

2014-01-30T19:02:10Z

Someone not using his real name:

Squeaky Dolphin

2014-01-30T18:59:49Z

Someone not using his real name:

Comodo Group

2014-01-23T02:54:34Z

Someone not using his real name: /* 2011 breach incident */

{{Infobox company
| name = Comodo Group, Inc.
| logo = [[File:Comodo logo.png]]
| type = [[Privately held company|Private]]
| company_slogan = Creating Trust
| foundation = [[United Kingdom]] ({{Start date|1998}}){{Citation needed|date=June 2013}}
| location_city = [[Clifton, New Jersey]]
| location_country = [[United States]]
| key_people = [[Melih Abdulhayoğlu]] ([[President]] and [[Chief executive officer|CEO]])
| num_employees = 1,100+
| industry = [[Computer security]], [[internet security]]
| products = {{Plainlist|
* Comodo Backup
* Comodo Cloud (cCloud)
* [[Comodo Endpoint Security Manager]]
* [[Comodo Internet Security]]
* Comodo HackerGuardian
* [[Comodo Mobile Security]]
* Comodo PC TuneUp
* [[Comodo SecureDNS]]
* Comodo SecureEmail
* [[Comodo SSL]]
* Comodo Web Inspector
* [[Comodo Dragon]]
* [[Comodo IceDragon]]
}}
| homepage = {{URL|www.comodo.com}}
}}
'''Comodo Group, Inc.''' is a privately held group of companies providing [[computer software]] and [[Transport Layer Security|SSL]] [[digital certificate]]s, based in [[Clifton, New Jersey]], [[United States]]. It has offices in the United Kingdom, Ukraine, Romania, China, India, Turkey and the United States.<ref name="comodoFactSheet">{{cite web|url=http://www.comodo.com/about/fact-sheet.php |title=Fact Sheet of Comodo Company - Creating Trust and Assurance - Comodo|publisher=comodo.com |date= |accessdate=2013-07-06}}</ref>

Comodo is the second most used [[certificate authority]] according to [[W3Techs]],<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage of SSL certificate authorities for websites |publisher=W3Techs.com |accessdate=October 19, 2013}}</ref> competing against [[Symantec]], [[Trend Micro]], [[DigiCert]], [[Entrust]], [[GlobalSign]], [[Go Daddy]], and others.

Comodo competes in the [[antivirus]] industry against [[Avira]], [[BullGuard]], [[F-Secure]], [[FRISK Software International|Frisk]], [[Kaspersky]], [[McAfee]], [[Panda Security]], [[Sophos]], [[Symantec]] and [[Trend Micro]] among [[List of antivirus software|others]].

==History==
The company was founded in 1998 in the United Kingdom, by Comodo CEO, [[Melih Abdulhayoğlu]], a technologist and an entrepreneur. Comodo relocated to the United States, first settling in [[Jersey City, New Jersey|Jersey City]], New Jersey in 2004. Comodo's product line is focused primarily on computer and internet security.<ref>{{cite news|last=Richmond|first=Riva|title=An Attack Sheds Light on Internet Security Holes|url=http://www.nytimes.com/2011/04/07/technology/07hack.html?_r=0|work=[[The New York Times]]|accessdate=17 March 2013|date=6 April 2011}}</ref> The firm operates a Certificate Authority that issues SSL certificates, offers a computer security suite that includes antivirus and firewall protection and offers other web and network protection services.

In December 2012 the company relocated its world headquarters from Jersey City to [[Clifton,_New_Jersey|Clifton]], New Jersey.<ref name="expressupdateusa1">{{cite web|url=http://listings.expressupdateusa.com/Business/NJ/Clifton/Comodo-Group-Inc/2019630004 |title=Comodo Group Inc - Clifton, NJ 07013 - (201) 963-0004 - Express Update Listing |publisher=Listings.expressupdateusa.com |date= |accessdate=2013-06-11}}</ref>

==Products==

===Certificate Authority===
{{Main|Comodo SSL}}
Comodo's largest and most prominent business is as a Certificate Authority that sells SSL Certificates. As of June 1, 2013 the company had a 27% Market Share among Certificate Authorities, just second behind Symantec, according to W3Tech.com<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage Statistics and Market Share of SSL Certificate Authorities for Websites, June 2013 |publisher=W3techs.com |date= |accessdate=2013-06-11}}</ref>

===Enterprise Products===
The Comodo strategy for the Enterprise market focuses primarily on cross selling web site PCI and Malware scanning services to their customers for SSL Certificates. They also market an End Point Security Management System that leverages their internet security software.

===Consumer Products===
The Comodo strategy for the consumer market is to offer its software products as [[freemium]]; that is, they are available for download free of charge,<ref>{{cite web
|url = http://www.techsupportalert.com/content/best-free-vista-64-bit-software.htm
|title = Best Free Windows 7 / Vista 64-bit Software
|work = Gizmo's Freeware
|date = 2 December 2010
|accessdate = 25 December 2010
}}</ref> but additional features and support are available for a fee.<ref name="tha-list">[http://www.comodo.com/products/comodo-products.php Products and Solutions]</ref> Among Comodo's free products is the [[Comodo Internet Security]], incorporating a [[personal firewall]], [[Host-based intrusion detection system]] and [[antivirus program]].<ref>{{cite web
|url = http://www.matousec.com/projects/proactive-security-challenge/results.php
|title = Proactive Security Challenge: Results and comments
|work = matousec.com
|publisher = Difinex Ltd
|accessdate = 25 December 2010
}}</ref> Other Comodo branded freeware security tools include an anti-malware tool, and a memory firewall that protects against over 90% of [[buffer overflow]] attacks.<ref>{{cite web
|url = http://www.techmixer.com/prevent-buffer-overflow-attack-with-comodo-memory-firewall/
|title = Prevent Buffer Overflow Attack with Comodo Memory Firewall
|work = TechMixer
|date = 26 September 2008 
|accessdate = 25 December 2010
}}</ref> For an additional fee, Comodo product users can subscribe to Comodo's computer cleaning and optimizing services for real-time computer assistance. Comodo also offers Comodo System Cleaner, which includes a free registry cleaner program,<ref>{{cite web
|url = http://www.pcworld.idg.com.au/index.php/taxid;2109929404;pid;7064;pt;1
|title = Comodo Registry Cleaner (PCWorld)
|work = [[PC World (magazine)|PC World Australia]]
|publisher = [[IDG Communications]]
|date = 2 December 2008
|last = Gralla
|first = Preston
|accessdate = 25 December 2010
}}</ref>

Comodo SecureEmail is an email encryption program that allows S/MIME email users to send emails to any email user without exchanging keys beforehand.
To support the mobile computing market Comodo has introduce the [[Comodo Mobile Security]] for the Android and Comodo Cloud storage for the Android and iOS.<ref>http://www.pcadvisor.co.uk/downloads/3329340/comodo-cloud-for-ios-and-android-20/</ref>

==Reception==

===Comodo Internet Security===
{{Main|Comodo Internet Security}}
Comodo Internet Security initially received mixed reviews; it was generally praised for its firewall and its value for price, but criticized for its poor antivirus detection. Over time, however, its antivirus component received better reviews. For instance, a 2008 review of Internet Security 3.5 from ''[[PC Magazine]]'' security analyst, Neil J. Rubenking, yielded a score of 2.5 out of 5, praising the suite's firewall and criticizing its antimalware component.<ref>{{cite journal|last=Rubenking,|first=Neil J.|title=Comodo Internet Security 3.5|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|date=3 November 2008|url=http://www.pcmag.com/article2/0,2817,2333803,00.asp|accessdate=7 March 2012}}</ref> Five years later, on 7 February 2013, Comodo Internet Security 2013 earned the ''PC Magazine'' Editor's Choice award. Neil J. Reubenking, reviewing the suite once again, gave it a score 4.5 of 5 stars.<ref name="Rubenking">{{cite web | url=http://www.pcmag.com/article2/0,2817,2415202,00.asp | title=Comodo Internet Security Complete 2013 | publisher=[[Ziff Davis]] | work=[[PC Magazine]] | date=7 February 2013 | accessdate=25 April 2013 | last=Rubenking | first=Neil J.}}</ref>

In response to [[Symantec]]'s comment over the effectiveness of free Antivirus software, on September 18, 2010, the CEO of Comodo Group [[Melih Abdulhayoğlu]] challenged Symantec to see which products can defend the consumer better against [[malware]].<ref>{{cite web
|url = http://www.melih.com/2010/09/18/challenge-to-symantec-from-comodo-ceo/
|title = Challenge to Symantec from Comodo CEO!
|first = Melih
|last = Abdulhayoğlu
|authorlink = Melih Abdulhayoğlu
|date = 18 September 2010
|publisher = Comodo Group
|accessdate = 22 September 2010
}}</ref> Symantec responded saying that if Comodo is interested they should have their product included in tests by independent reviewers.<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369524,00.asp
|title = Comodo Challenges Symantec to Antivirus Showdown
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 22 September 2010
|accessdate = 22 September 2010
}}</ref> On 29 September 2010, Neil J. Rubenking, the lead analyst for security of PC Magazine, published an article on Comodo Antivirus 5.0 that<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369897,00.asp
|title = Comodo Antivirus 5.0
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date=29 September 2010
|accessdate=29 September 2010
}}</ref><ref>{{cite news
|url = http://www.pcmag.com/image_popup/0,1871,iid=270708,00.asp
|title = Comodo Antivirus 5.0 malware blocking chart
|first = Neil J. Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 29 September 2010
|accessdate=29 September 2010
}}</ref> concluded that Comodo Antivirus 5.0 blocked a higher percentage of malware than Norton AntiVirus, but was less effective than the Norton solution when it came to malware removal. Rubenking's review also noted that the Comodo malware blocking gave a number of false positives which he felt tarnished Comodo's results.

In a 9 January 2013 review, ''Techworld'' awarded Comodo Internet Security Pro 2013 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."<ref>{{cite web | url=http://download.techworld.com/3328878/comodo-internet-security-pro-2013-v60/ | title=Comodo Internet Security Pro 2013 (v6.1) | publisher=[[IDG]] | work=TechWorld | date=9 January 2013 | accessdate=25 April 2013}}</ref> Also on the same date, Mike Williams of ''BetaNews.com'' reviewed Comodo Internet Security Pro 2013 and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."<ref>{{cite web | url=http://betanews.com/2013/01/09/comodo-internet-security-pro-2013-review/ | title=Comodo Internet Security Pro 2013 [Review] | work=BetaNews | date=9 January 2013 | accessdate=25 April 2013 | first=Mike | last=Williams}}</ref>

On 7 February 2013, Comodo Internet Security Complete v6 earned the ''PC Magazine'' Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score 4.5 of 5 stars, commended its support service, VPN solution, DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete 2013 isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."<ref name="Rubenking"/>

In October 2013, TopTenReviews.com reviewed the Comodo Internet Security 2014 Complete edition and gave it a score of 9.18 out of 10. Their review notes that the firewall component is their Gold Award winner for best firewall protection. However, they also comment on the lack of brand name recognition for Comodo's product.<ref>http://personal-firewall-software-review.toptenreviews.com/comodo-internet-security-pro-review.html</ref>

===Comodo PC TuneUp===
{{Main|Comodo System Utilities}}
In August 2012, Jeffery L. Wilson of PCMag.com gave Comodo System Utilities an Excellent rating, 4 of 5 stars. He states as his "Bottom Line" conclusion "Comodo System Utilities is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps".<ref name=PCMag.com>{{cite web|title=Comodo System Utilities Review|url=http://www.pcmag.com/article2/0,2817,2370702,00.asp}}</ref>

In 2013 Comodo System Utilities was rebranded as Comodo PC TuneUP.
In October 2013, PCMag gave PC TuneUp an Editor's rating of "Good". Jeffery Sacks wrote "Comodo PC Tuneup is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps."<ref>http://www.pcmag.com/article2/0,2817,2370702,00.asp</ref>

===Comodo Dragon Web Browser===
{{Main|Comodo Dragon (web browser)}}
On June 17, 2010 a cNET Editor's review gave the Comodo Dragon a 5 of 5 star score and a rating of Spectacular. they concluded "Dragon is not only fast, but like Google Chrome, it is not strewn with numerous icons, leaving more room for Web viewing. For those who are extra cautious about their online security, or for those who are worried about Google's data-mining, this fast browser is a great choice.
<ref>{{cite web|author=From Comodo: |url=http://download.cnet.com/Comodo-Dragon/3000-2356_4-75119680.html |title=Comodo Dragon - CNET Download.com |publisher=Download.cnet.com |date= |accessdate=2013-06-11}}</ref>

== Industry affiliations ==
Comodo is a member of the following industry organizations:
* [[Certificate Authority Security Council]] (CASC): In February 2013, Comodo became a founding member of this industry advocacy organization dedicated to addressing industry issues and educating the public on internet security.<ref>http://www.networkworld.com/news/2013/021413-council-digital-certificate-266728.html</ref><ref>http://www.darkreading.com/authentication/167901072/security/news/240148546/major-certificate-authorities-unite-in-the-name-of-ssl-security.html</ref>
* [[Common Computing Security Standards Forum]](CCSF): In 2009 Comodo was a founding member of the CCSF, an industry organization that promotes industry standards that protect end users. Comodo CEO Melih Abdulhayoğlu is considered the founder of the CCSF.<ref>http://www.securitypark.co.uk/</ref>
* [[CA/Browser Forum]]: In 2005, Comodo was a founding member of a new consortium of Certificate Authorities and web browser vendors dedicated to promoting industry standards and baseline requirements for internet security.<ref>{{cite web | url=https://www.cabforum.org/ | title=CA/Browser Forum | accessdate=2013-04-23}}</ref><ref>{{cite web | url=http://docbox.etsi.org/workshop/2012/201201_CA_DAY/5_Wilson_CAB-Forum.pdf | title=CA/Browser Forum History | last = Wilson | first = Wilson | publisher = DigiCert | accessdate=2013-04-23}}</ref>

==2011 breach incident==
On March 15, 2011, Comodo reported that a user account with an affiliate registration authority had been compromised which was used to create a new user account that issued nine [[certificate signing request]]s.<ref name="comodo inc1">{{cite web|title=Report of incident on 15-MAR-2011|url=https://www.comodo.com/Comodo-Fraud-Incident-2011-03-23.html|accessdate=2011-03-24|publisher=Comodo group}}</ref> Nine certificates for seven domains were issued.<ref name="comodo inc1"/> Comodo responded by revoking the nine certificates.<ref name="comodo inc1"/> Microsoft also issued a security advisory and update to address the issue.<ref>{{cite web|title=Microsoft Security Advisory (2524375)|url=http://www.microsoft.com/technet/security/advisory/2524375.mspx|date=March 23, 2011|accessdate=2011-03-24|format=Microsoft}}</ref><ref>{{cite web|title=Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing|url=http://support.microsoft.com/kb/2524375|date=March 23, 2011|accessdate=2011-03-24|work=Microsoft}}</ref>

The attack was traced to IP address 212.95.136.18, which originates in Tehran, Iran.<ref name="comodo inc1"/> Though Comodo initially reported the breach was the result of a "state-driven attack", it subsequently stated that the origin of the attack may be the "result of an attacker attempting to lay a false trail."<ref name="comodo inc1"/><ref name="comodo blog1">{{cite web|title=The Recent RA Compromise|url=http://blogs.comodo.com/it-security/data-security/the-recent-ca-compromise/|first=Phillip|last= Hallam-Baker|date=March 23, 2011 |accessdate=2011-03-24|publisher=Comodo Blog}}</ref> The issue, however, led to criticism of how certificates are issued and revoked.<ref>{{cite web|title=Iranian hackers obtain fraudulent HTTPS certificates: How close to a Web security meltdown did we get?|url=https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https|first=Peter |last=Eckersley|date=March 23, 2011|accessdate=2011-03-24|work=EFF}}</ref><ref>{{cite news|title=Iran accused in 'dire' net security attack|url=http://www.bbc.co.uk/news/technology-12847072|date=March 24, 2011|format=BBC|accessdate=2011-03-24|work=BBC News}}</ref><ref>{{cite web|title=Detecting Certificate Authority compromises and web browser collusion |url=https://blog.torproject.org/blog/detecting-certificate-authority-compromises-and-web-browser-collusion|date=March 22, 2011|accessdate=2011-03-24|work=TOR}}</ref><ref>{{cite news|title=Google, Yahoo, Skype targeted in attack linked to Iran|url=http://news.cnet.com/8301-31921_3-20046340-281.html|date=March 23, 2011|author1=Elinor Mills |author2=Declan McCullagh|work=CNET|accessdate=2011-03-24}}</ref>

On March 26, 2011, a person under the username "ComodoHacker" made several posts to [[Pastebin]].com claiming to be an Iranian responsible for the attack against Comodo.<ref>{{cite news|title=Independent Iranian Hacker Claims Responsibility for Comodo Hack|url=http://www.wired.com/threatlevel/2011/03/comodo_hack/|first=Peter |last=Bright|date=March 28, 2011|format=WIRED|accessdate=2011-03-29|work=Wired}}</ref><ref>{{cite web|title=ComodoHacker's Pastebin|url=http://pastebin.com/u/ComodoHacker}}</ref> In September 2011, the same hacker claimed attacks against four other CAs, including [[GlobalSign]] and [[DigiNotar]], resulting in a closure of the latter.<Ref>http://www.pcworld.idg.com.au/article/399812/comodo_hacker_claims_credit_diginotar_attack/</ref>

==References==
{{reflist|30em}}

==External links==
* {{Official website|www.comodo.com}}
* [http://www.antivirus.comodo.com Comodo Antivirus]

[[Category:Companies established in 1998]]
[[Category:Certificate authorities]]
[[Category:Computer security software companies]]
[[Category:Computer companies of the United States]]
[[Category:Comodo Group| ]]

Comodo Group

2014-01-23T02:37:39Z

Someone not using his real name: /* 2011 breach incident */

{{Infobox company
| name = Comodo Group, Inc.
| logo = [[File:Comodo logo.png]]
| type = [[Privately held company|Private]]
| company_slogan = Creating Trust
| foundation = [[United Kingdom]] ({{Start date|1998}}){{Citation needed|date=June 2013}}
| location_city = [[Clifton, New Jersey]]
| location_country = [[United States]]
| key_people = [[Melih Abdulhayoğlu]] ([[President]] and [[Chief executive officer|CEO]])
| num_employees = 1,100+
| industry = [[Computer security]], [[internet security]]
| products = {{Plainlist|
* Comodo Backup
* Comodo Cloud (cCloud)
* [[Comodo Endpoint Security Manager]]
* [[Comodo Internet Security]]
* Comodo HackerGuardian
* [[Comodo Mobile Security]]
* Comodo PC TuneUp
* [[Comodo SecureDNS]]
* Comodo SecureEmail
* [[Comodo SSL]]
* Comodo Web Inspector
* [[Comodo Dragon]]
* [[Comodo IceDragon]]
}}
| homepage = {{URL|www.comodo.com}}
}}
'''Comodo Group, Inc.''' is a privately held group of companies providing [[computer software]] and [[Transport Layer Security|SSL]] [[digital certificate]]s, based in [[Clifton, New Jersey]], [[United States]]. It has offices in the United Kingdom, Ukraine, Romania, China, India, Turkey and the United States.<ref name="comodoFactSheet">{{cite web|url=http://www.comodo.com/about/fact-sheet.php |title=Fact Sheet of Comodo Company - Creating Trust and Assurance - Comodo|publisher=comodo.com |date= |accessdate=2013-07-06}}</ref>

Comodo is the second most used [[certificate authority]] according to [[W3Techs]],<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage of SSL certificate authorities for websites |publisher=W3Techs.com |accessdate=October 19, 2013}}</ref> competing against [[Symantec]], [[Trend Micro]], [[DigiCert]], [[Entrust]], [[GlobalSign]], [[Go Daddy]], and others.

Comodo competes in the [[antivirus]] industry against [[Avira]], [[BullGuard]], [[F-Secure]], [[FRISK Software International|Frisk]], [[Kaspersky]], [[McAfee]], [[Panda Security]], [[Sophos]], [[Symantec]] and [[Trend Micro]] among [[List of antivirus software|others]].

==History==
The company was founded in 1998 in the United Kingdom, by Comodo CEO, [[Melih Abdulhayoğlu]], a technologist and an entrepreneur. Comodo relocated to the United States, first settling in [[Jersey City, New Jersey|Jersey City]], New Jersey in 2004. Comodo's product line is focused primarily on computer and internet security.<ref>{{cite news|last=Richmond|first=Riva|title=An Attack Sheds Light on Internet Security Holes|url=http://www.nytimes.com/2011/04/07/technology/07hack.html?_r=0|work=[[The New York Times]]|accessdate=17 March 2013|date=6 April 2011}}</ref> The firm operates a Certificate Authority that issues SSL certificates, offers a computer security suite that includes antivirus and firewall protection and offers other web and network protection services.

In December 2012 the company relocated its world headquarters from Jersey City to [[Clifton,_New_Jersey|Clifton]], New Jersey.<ref name="expressupdateusa1">{{cite web|url=http://listings.expressupdateusa.com/Business/NJ/Clifton/Comodo-Group-Inc/2019630004 |title=Comodo Group Inc - Clifton, NJ 07013 - (201) 963-0004 - Express Update Listing |publisher=Listings.expressupdateusa.com |date= |accessdate=2013-06-11}}</ref>

==Products==

===Certificate Authority===
{{Main|Comodo SSL}}
Comodo's largest and most prominent business is as a Certificate Authority that sells SSL Certificates. As of June 1, 2013 the company had a 27% Market Share among Certificate Authorities, just second behind Symantec, according to W3Tech.com<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage Statistics and Market Share of SSL Certificate Authorities for Websites, June 2013 |publisher=W3techs.com |date= |accessdate=2013-06-11}}</ref>

===Enterprise Products===
The Comodo strategy for the Enterprise market focuses primarily on cross selling web site PCI and Malware scanning services to their customers for SSL Certificates. They also market an End Point Security Management System that leverages their internet security software.

===Consumer Products===
The Comodo strategy for the consumer market is to offer its software products as [[freemium]]; that is, they are available for download free of charge,<ref>{{cite web
|url = http://www.techsupportalert.com/content/best-free-vista-64-bit-software.htm
|title = Best Free Windows 7 / Vista 64-bit Software
|work = Gizmo's Freeware
|date = 2 December 2010
|accessdate = 25 December 2010
}}</ref> but additional features and support are available for a fee.<ref name="tha-list">[http://www.comodo.com/products/comodo-products.php Products and Solutions]</ref> Among Comodo's free products is the [[Comodo Internet Security]], incorporating a [[personal firewall]], [[Host-based intrusion detection system]] and [[antivirus program]].<ref>{{cite web
|url = http://www.matousec.com/projects/proactive-security-challenge/results.php
|title = Proactive Security Challenge: Results and comments
|work = matousec.com
|publisher = Difinex Ltd
|accessdate = 25 December 2010
}}</ref> Other Comodo branded freeware security tools include an anti-malware tool, and a memory firewall that protects against over 90% of [[buffer overflow]] attacks.<ref>{{cite web
|url = http://www.techmixer.com/prevent-buffer-overflow-attack-with-comodo-memory-firewall/
|title = Prevent Buffer Overflow Attack with Comodo Memory Firewall
|work = TechMixer
|date = 26 September 2008 
|accessdate = 25 December 2010
}}</ref> For an additional fee, Comodo product users can subscribe to Comodo's computer cleaning and optimizing services for real-time computer assistance. Comodo also offers Comodo System Cleaner, which includes a free registry cleaner program,<ref>{{cite web
|url = http://www.pcworld.idg.com.au/index.php/taxid;2109929404;pid;7064;pt;1
|title = Comodo Registry Cleaner (PCWorld)
|work = [[PC World (magazine)|PC World Australia]]
|publisher = [[IDG Communications]]
|date = 2 December 2008
|last = Gralla
|first = Preston
|accessdate = 25 December 2010
}}</ref>

Comodo SecureEmail is an email encryption program that allows S/MIME email users to send emails to any email user without exchanging keys beforehand.
To support the mobile computing market Comodo has introduce the [[Comodo Mobile Security]] for the Android and Comodo Cloud storage for the Android and iOS.<ref>http://www.pcadvisor.co.uk/downloads/3329340/comodo-cloud-for-ios-and-android-20/</ref>

==Reception==

===Comodo Internet Security===
{{Main|Comodo Internet Security}}
Comodo Internet Security initially received mixed reviews; it was generally praised for its firewall and its value for price, but criticized for its poor antivirus detection. Over time, however, its antivirus component received better reviews. For instance, a 2008 review of Internet Security 3.5 from ''[[PC Magazine]]'' security analyst, Neil J. Rubenking, yielded a score of 2.5 out of 5, praising the suite's firewall and criticizing its antimalware component.<ref>{{cite journal|last=Rubenking,|first=Neil J.|title=Comodo Internet Security 3.5|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|date=3 November 2008|url=http://www.pcmag.com/article2/0,2817,2333803,00.asp|accessdate=7 March 2012}}</ref> Five years later, on 7 February 2013, Comodo Internet Security 2013 earned the ''PC Magazine'' Editor's Choice award. Neil J. Reubenking, reviewing the suite once again, gave it a score 4.5 of 5 stars.<ref name="Rubenking">{{cite web | url=http://www.pcmag.com/article2/0,2817,2415202,00.asp | title=Comodo Internet Security Complete 2013 | publisher=[[Ziff Davis]] | work=[[PC Magazine]] | date=7 February 2013 | accessdate=25 April 2013 | last=Rubenking | first=Neil J.}}</ref>

In response to [[Symantec]]'s comment over the effectiveness of free Antivirus software, on September 18, 2010, the CEO of Comodo Group [[Melih Abdulhayoğlu]] challenged Symantec to see which products can defend the consumer better against [[malware]].<ref>{{cite web
|url = http://www.melih.com/2010/09/18/challenge-to-symantec-from-comodo-ceo/
|title = Challenge to Symantec from Comodo CEO!
|first = Melih
|last = Abdulhayoğlu
|authorlink = Melih Abdulhayoğlu
|date = 18 September 2010
|publisher = Comodo Group
|accessdate = 22 September 2010
}}</ref> Symantec responded saying that if Comodo is interested they should have their product included in tests by independent reviewers.<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369524,00.asp
|title = Comodo Challenges Symantec to Antivirus Showdown
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 22 September 2010
|accessdate = 22 September 2010
}}</ref> On 29 September 2010, Neil J. Rubenking, the lead analyst for security of PC Magazine, published an article on Comodo Antivirus 5.0 that<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369897,00.asp
|title = Comodo Antivirus 5.0
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date=29 September 2010
|accessdate=29 September 2010
}}</ref><ref>{{cite news
|url = http://www.pcmag.com/image_popup/0,1871,iid=270708,00.asp
|title = Comodo Antivirus 5.0 malware blocking chart
|first = Neil J. Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 29 September 2010
|accessdate=29 September 2010
}}</ref> concluded that Comodo Antivirus 5.0 blocked a higher percentage of malware than Norton AntiVirus, but was less effective than the Norton solution when it came to malware removal. Rubenking's review also noted that the Comodo malware blocking gave a number of false positives which he felt tarnished Comodo's results.

In a 9 January 2013 review, ''Techworld'' awarded Comodo Internet Security Pro 2013 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."<ref>{{cite web | url=http://download.techworld.com/3328878/comodo-internet-security-pro-2013-v60/ | title=Comodo Internet Security Pro 2013 (v6.1) | publisher=[[IDG]] | work=TechWorld | date=9 January 2013 | accessdate=25 April 2013}}</ref> Also on the same date, Mike Williams of ''BetaNews.com'' reviewed Comodo Internet Security Pro 2013 and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."<ref>{{cite web | url=http://betanews.com/2013/01/09/comodo-internet-security-pro-2013-review/ | title=Comodo Internet Security Pro 2013 [Review] | work=BetaNews | date=9 January 2013 | accessdate=25 April 2013 | first=Mike | last=Williams}}</ref>

On 7 February 2013, Comodo Internet Security Complete v6 earned the ''PC Magazine'' Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score 4.5 of 5 stars, commended its support service, VPN solution, DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete 2013 isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."<ref name="Rubenking"/>

In October 2013, TopTenReviews.com reviewed the Comodo Internet Security 2014 Complete edition and gave it a score of 9.18 out of 10. Their review notes that the firewall component is their Gold Award winner for best firewall protection. However, they also comment on the lack of brand name recognition for Comodo's product.<ref>http://personal-firewall-software-review.toptenreviews.com/comodo-internet-security-pro-review.html</ref>

===Comodo PC TuneUp===
{{Main|Comodo System Utilities}}
In August 2012, Jeffery L. Wilson of PCMag.com gave Comodo System Utilities an Excellent rating, 4 of 5 stars. He states as his "Bottom Line" conclusion "Comodo System Utilities is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps".<ref name=PCMag.com>{{cite web|title=Comodo System Utilities Review|url=http://www.pcmag.com/article2/0,2817,2370702,00.asp}}</ref>

In 2013 Comodo System Utilities was rebranded as Comodo PC TuneUP.
In October 2013, PCMag gave PC TuneUp an Editor's rating of "Good". Jeffery Sacks wrote "Comodo PC Tuneup is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps."<ref>http://www.pcmag.com/article2/0,2817,2370702,00.asp</ref>

===Comodo Dragon Web Browser===
{{Main|Comodo Dragon (web browser)}}
On June 17, 2010 a cNET Editor's review gave the Comodo Dragon a 5 of 5 star score and a rating of Spectacular. they concluded "Dragon is not only fast, but like Google Chrome, it is not strewn with numerous icons, leaving more room for Web viewing. For those who are extra cautious about their online security, or for those who are worried about Google's data-mining, this fast browser is a great choice.
<ref>{{cite web|author=From Comodo: |url=http://download.cnet.com/Comodo-Dragon/3000-2356_4-75119680.html |title=Comodo Dragon - CNET Download.com |publisher=Download.cnet.com |date= |accessdate=2013-06-11}}</ref>

== Industry affiliations ==
Comodo is a member of the following industry organizations:
* [[Certificate Authority Security Council]] (CASC): In February 2013, Comodo became a founding member of this industry advocacy organization dedicated to addressing industry issues and educating the public on internet security.<ref>http://www.networkworld.com/news/2013/021413-council-digital-certificate-266728.html</ref><ref>http://www.darkreading.com/authentication/167901072/security/news/240148546/major-certificate-authorities-unite-in-the-name-of-ssl-security.html</ref>
* [[Common Computing Security Standards Forum]](CCSF): In 2009 Comodo was a founding member of the CCSF, an industry organization that promotes industry standards that protect end users. Comodo CEO Melih Abdulhayoğlu is considered the founder of the CCSF.<ref>http://www.securitypark.co.uk/</ref>
* [[CA/Browser Forum]]: In 2005, Comodo was a founding member of a new consortium of Certificate Authorities and web browser vendors dedicated to promoting industry standards and baseline requirements for internet security.<ref>{{cite web | url=https://www.cabforum.org/ | title=CA/Browser Forum | accessdate=2013-04-23}}</ref><ref>{{cite web | url=http://docbox.etsi.org/workshop/2012/201201_CA_DAY/5_Wilson_CAB-Forum.pdf | title=CA/Browser Forum History | last = Wilson | first = Wilson | publisher = DigiCert | accessdate=2013-04-23}}</ref>

==2011 breach incident==
On March 15, 2011, Comodo reported that a user account with an affiliate registration authority had been compromised which was used to create a new user account that issued nine [[certificate signing request]]s.<ref name="comodo inc1">{{cite web|title=Report of incident on 15-MAR-2011|url=https://www.comodo.com/Comodo-Fraud-Incident-2011-03-23.html|accessdate=2011-03-24|publisher=Comodo group}}</ref> Nine certificates for seven domains were issued.<ref name="comodo inc1"/> Comodo responded by revoking the nine certificates.<ref name="comodo inc1"/> Microsoft also issued a security advisory and update to address the issue.<ref>{{cite web|title=Microsoft Security Advisory (2524375)|url=http://www.microsoft.com/technet/security/advisory/2524375.mspx|date=March 23, 2011|accessdate=2011-03-24|format=Microsoft}}</ref><ref>{{cite web|title=Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing|url=http://support.microsoft.com/kb/2524375|date=March 23, 2011|accessdate=2011-03-24|work=Microsoft}}</ref>

The attack was traced to IP address 212.95.136.18, which originates in Tehran, Iran.<ref name="comodo inc1"/> Though Comodo initially reported the breach was the result of a "state-driven attack", it subsequently stated that the origin of the attack may be the "result of an attacker attempting to lay a false trail."<ref name="comodo inc1"/><ref name="comodo blog1">{{cite web|title=The Recent RA Compromise|url=http://blogs.comodo.com/it-security/data-security/the-recent-ca-compromise/|first=Phillip|last= Hallam-Baker|date=March 23, 2011 |accessdate=2011-03-24|publisher=Comodo Blog}}</ref> The issue, however, led to criticism of how certificates are issued and revoked.<ref>{{cite web|title=Iranian hackers obtain fraudulent HTTPS certificates: How close to a Web security meltdown did we get?|url=https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https|first=Peter |last=Eckersley|date=March 23, 2011|accessdate=2011-03-24|work=EFF}}</ref><ref>{{cite news|title=Iran accused in 'dire' net security attack|url=http://www.bbc.co.uk/news/technology-12847072|date=March 24, 2011|format=BBC|accessdate=2011-03-24|work=BBC News}}</ref><ref>{{cite web|title=Detecting Certificate Authority compromises and web browser collusion |url=https://blog.torproject.org/blog/detecting-certificate-authority-compromises-and-web-browser-collusion|date=March 22, 2011|accessdate=2011-03-24|work=TOR}}</ref><ref>{{cite news|title=Google, Yahoo, Skype targeted in attack linked to Iran|url=http://news.cnet.com/8301-31921_3-20046340-281.html|date=March 23, 2011|author1=Elinor Mills |author2=Declan McCullagh|work=CNET|accessdate=2011-03-24}}</ref>

On March 26, 2011, a person under the username "ComodoHacker" made several posts to [[Pastebin]].com claiming to be an Iranian responsible for the attack against Comodo.<ref>{{cite news|title=Independent Iranian Hacker Claims Responsibility for Comodo Hack|url=http://www.wired.com/threatlevel/2011/03/comodo_hack/|first=Peter |last=Bright|date=March 28, 2011|format=WIRED|accessdate=2011-03-29|work=Wired}}</ref><ref>{{cite web|title=ComodoHacker's Pastebin|url=http://pastebin.com/u/ComodoHacker}}</ref> In September 2011, the same hacker claimed attacks against four other CAs, including [[DigiNotar]], which closed in the aftermath.<Ref>http://www.pcworld.idg.com.au/article/399812/comodo_hacker_claims_credit_diginotar_attack/</ref>

==References==
{{reflist|30em}}

==External links==
* {{Official website|www.comodo.com}}
* [http://www.antivirus.comodo.com Comodo Antivirus]

[[Category:Companies established in 1998]]
[[Category:Certificate authorities]]
[[Category:Computer security software companies]]
[[Category:Computer companies of the United States]]
[[Category:Comodo Group| ]]

Comodo Group

2014-01-23T02:36:39Z

Someone not using his real name: /* 2011 breach incident */

{{Infobox company
| name = Comodo Group, Inc.
| logo = [[File:Comodo logo.png]]
| type = [[Privately held company|Private]]
| company_slogan = Creating Trust
| foundation = [[United Kingdom]] ({{Start date|1998}}){{Citation needed|date=June 2013}}
| location_city = [[Clifton, New Jersey]]
| location_country = [[United States]]
| key_people = [[Melih Abdulhayoğlu]] ([[President]] and [[Chief executive officer|CEO]])
| num_employees = 1,100+
| industry = [[Computer security]], [[internet security]]
| products = {{Plainlist|
* Comodo Backup
* Comodo Cloud (cCloud)
* [[Comodo Endpoint Security Manager]]
* [[Comodo Internet Security]]
* Comodo HackerGuardian
* [[Comodo Mobile Security]]
* Comodo PC TuneUp
* [[Comodo SecureDNS]]
* Comodo SecureEmail
* [[Comodo SSL]]
* Comodo Web Inspector
* [[Comodo Dragon]]
* [[Comodo IceDragon]]
}}
| homepage = {{URL|www.comodo.com}}
}}
'''Comodo Group, Inc.''' is a privately held group of companies providing [[computer software]] and [[Transport Layer Security|SSL]] [[digital certificate]]s, based in [[Clifton, New Jersey]], [[United States]]. It has offices in the United Kingdom, Ukraine, Romania, China, India, Turkey and the United States.<ref name="comodoFactSheet">{{cite web|url=http://www.comodo.com/about/fact-sheet.php |title=Fact Sheet of Comodo Company - Creating Trust and Assurance - Comodo|publisher=comodo.com |date= |accessdate=2013-07-06}}</ref>

Comodo is the second most used [[certificate authority]] according to [[W3Techs]],<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage of SSL certificate authorities for websites |publisher=W3Techs.com |accessdate=October 19, 2013}}</ref> competing against [[Symantec]], [[Trend Micro]], [[DigiCert]], [[Entrust]], [[GlobalSign]], [[Go Daddy]], and others.

Comodo competes in the [[antivirus]] industry against [[Avira]], [[BullGuard]], [[F-Secure]], [[FRISK Software International|Frisk]], [[Kaspersky]], [[McAfee]], [[Panda Security]], [[Sophos]], [[Symantec]] and [[Trend Micro]] among [[List of antivirus software|others]].

==History==
The company was founded in 1998 in the United Kingdom, by Comodo CEO, [[Melih Abdulhayoğlu]], a technologist and an entrepreneur. Comodo relocated to the United States, first settling in [[Jersey City, New Jersey|Jersey City]], New Jersey in 2004. Comodo's product line is focused primarily on computer and internet security.<ref>{{cite news|last=Richmond|first=Riva|title=An Attack Sheds Light on Internet Security Holes|url=http://www.nytimes.com/2011/04/07/technology/07hack.html?_r=0|work=[[The New York Times]]|accessdate=17 March 2013|date=6 April 2011}}</ref> The firm operates a Certificate Authority that issues SSL certificates, offers a computer security suite that includes antivirus and firewall protection and offers other web and network protection services.

In December 2012 the company relocated its world headquarters from Jersey City to [[Clifton,_New_Jersey|Clifton]], New Jersey.<ref name="expressupdateusa1">{{cite web|url=http://listings.expressupdateusa.com/Business/NJ/Clifton/Comodo-Group-Inc/2019630004 |title=Comodo Group Inc - Clifton, NJ 07013 - (201) 963-0004 - Express Update Listing |publisher=Listings.expressupdateusa.com |date= |accessdate=2013-06-11}}</ref>

==Products==

===Certificate Authority===
{{Main|Comodo SSL}}
Comodo's largest and most prominent business is as a Certificate Authority that sells SSL Certificates. As of June 1, 2013 the company had a 27% Market Share among Certificate Authorities, just second behind Symantec, according to W3Tech.com<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage Statistics and Market Share of SSL Certificate Authorities for Websites, June 2013 |publisher=W3techs.com |date= |accessdate=2013-06-11}}</ref>

===Enterprise Products===
The Comodo strategy for the Enterprise market focuses primarily on cross selling web site PCI and Malware scanning services to their customers for SSL Certificates. They also market an End Point Security Management System that leverages their internet security software.

===Consumer Products===
The Comodo strategy for the consumer market is to offer its software products as [[freemium]]; that is, they are available for download free of charge,<ref>{{cite web
|url = http://www.techsupportalert.com/content/best-free-vista-64-bit-software.htm
|title = Best Free Windows 7 / Vista 64-bit Software
|work = Gizmo's Freeware
|date = 2 December 2010
|accessdate = 25 December 2010
}}</ref> but additional features and support are available for a fee.<ref name="tha-list">[http://www.comodo.com/products/comodo-products.php Products and Solutions]</ref> Among Comodo's free products is the [[Comodo Internet Security]], incorporating a [[personal firewall]], [[Host-based intrusion detection system]] and [[antivirus program]].<ref>{{cite web
|url = http://www.matousec.com/projects/proactive-security-challenge/results.php
|title = Proactive Security Challenge: Results and comments
|work = matousec.com
|publisher = Difinex Ltd
|accessdate = 25 December 2010
}}</ref> Other Comodo branded freeware security tools include an anti-malware tool, and a memory firewall that protects against over 90% of [[buffer overflow]] attacks.<ref>{{cite web
|url = http://www.techmixer.com/prevent-buffer-overflow-attack-with-comodo-memory-firewall/
|title = Prevent Buffer Overflow Attack with Comodo Memory Firewall
|work = TechMixer
|date = 26 September 2008 
|accessdate = 25 December 2010
}}</ref> For an additional fee, Comodo product users can subscribe to Comodo's computer cleaning and optimizing services for real-time computer assistance. Comodo also offers Comodo System Cleaner, which includes a free registry cleaner program,<ref>{{cite web
|url = http://www.pcworld.idg.com.au/index.php/taxid;2109929404;pid;7064;pt;1
|title = Comodo Registry Cleaner (PCWorld)
|work = [[PC World (magazine)|PC World Australia]]
|publisher = [[IDG Communications]]
|date = 2 December 2008
|last = Gralla
|first = Preston
|accessdate = 25 December 2010
}}</ref>

Comodo SecureEmail is an email encryption program that allows S/MIME email users to send emails to any email user without exchanging keys beforehand.
To support the mobile computing market Comodo has introduce the [[Comodo Mobile Security]] for the Android and Comodo Cloud storage for the Android and iOS.<ref>http://www.pcadvisor.co.uk/downloads/3329340/comodo-cloud-for-ios-and-android-20/</ref>

==Reception==

===Comodo Internet Security===
{{Main|Comodo Internet Security}}
Comodo Internet Security initially received mixed reviews; it was generally praised for its firewall and its value for price, but criticized for its poor antivirus detection. Over time, however, its antivirus component received better reviews. For instance, a 2008 review of Internet Security 3.5 from ''[[PC Magazine]]'' security analyst, Neil J. Rubenking, yielded a score of 2.5 out of 5, praising the suite's firewall and criticizing its antimalware component.<ref>{{cite journal|last=Rubenking,|first=Neil J.|title=Comodo Internet Security 3.5|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|date=3 November 2008|url=http://www.pcmag.com/article2/0,2817,2333803,00.asp|accessdate=7 March 2012}}</ref> Five years later, on 7 February 2013, Comodo Internet Security 2013 earned the ''PC Magazine'' Editor's Choice award. Neil J. Reubenking, reviewing the suite once again, gave it a score 4.5 of 5 stars.<ref name="Rubenking">{{cite web | url=http://www.pcmag.com/article2/0,2817,2415202,00.asp | title=Comodo Internet Security Complete 2013 | publisher=[[Ziff Davis]] | work=[[PC Magazine]] | date=7 February 2013 | accessdate=25 April 2013 | last=Rubenking | first=Neil J.}}</ref>

In response to [[Symantec]]'s comment over the effectiveness of free Antivirus software, on September 18, 2010, the CEO of Comodo Group [[Melih Abdulhayoğlu]] challenged Symantec to see which products can defend the consumer better against [[malware]].<ref>{{cite web
|url = http://www.melih.com/2010/09/18/challenge-to-symantec-from-comodo-ceo/
|title = Challenge to Symantec from Comodo CEO!
|first = Melih
|last = Abdulhayoğlu
|authorlink = Melih Abdulhayoğlu
|date = 18 September 2010
|publisher = Comodo Group
|accessdate = 22 September 2010
}}</ref> Symantec responded saying that if Comodo is interested they should have their product included in tests by independent reviewers.<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369524,00.asp
|title = Comodo Challenges Symantec to Antivirus Showdown
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 22 September 2010
|accessdate = 22 September 2010
}}</ref> On 29 September 2010, Neil J. Rubenking, the lead analyst for security of PC Magazine, published an article on Comodo Antivirus 5.0 that<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369897,00.asp
|title = Comodo Antivirus 5.0
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date=29 September 2010
|accessdate=29 September 2010
}}</ref><ref>{{cite news
|url = http://www.pcmag.com/image_popup/0,1871,iid=270708,00.asp
|title = Comodo Antivirus 5.0 malware blocking chart
|first = Neil J. Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 29 September 2010
|accessdate=29 September 2010
}}</ref> concluded that Comodo Antivirus 5.0 blocked a higher percentage of malware than Norton AntiVirus, but was less effective than the Norton solution when it came to malware removal. Rubenking's review also noted that the Comodo malware blocking gave a number of false positives which he felt tarnished Comodo's results.

In a 9 January 2013 review, ''Techworld'' awarded Comodo Internet Security Pro 2013 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."<ref>{{cite web | url=http://download.techworld.com/3328878/comodo-internet-security-pro-2013-v60/ | title=Comodo Internet Security Pro 2013 (v6.1) | publisher=[[IDG]] | work=TechWorld | date=9 January 2013 | accessdate=25 April 2013}}</ref> Also on the same date, Mike Williams of ''BetaNews.com'' reviewed Comodo Internet Security Pro 2013 and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."<ref>{{cite web | url=http://betanews.com/2013/01/09/comodo-internet-security-pro-2013-review/ | title=Comodo Internet Security Pro 2013 [Review] | work=BetaNews | date=9 January 2013 | accessdate=25 April 2013 | first=Mike | last=Williams}}</ref>

On 7 February 2013, Comodo Internet Security Complete v6 earned the ''PC Magazine'' Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score 4.5 of 5 stars, commended its support service, VPN solution, DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete 2013 isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."<ref name="Rubenking"/>

In October 2013, TopTenReviews.com reviewed the Comodo Internet Security 2014 Complete edition and gave it a score of 9.18 out of 10. Their review notes that the firewall component is their Gold Award winner for best firewall protection. However, they also comment on the lack of brand name recognition for Comodo's product.<ref>http://personal-firewall-software-review.toptenreviews.com/comodo-internet-security-pro-review.html</ref>

===Comodo PC TuneUp===
{{Main|Comodo System Utilities}}
In August 2012, Jeffery L. Wilson of PCMag.com gave Comodo System Utilities an Excellent rating, 4 of 5 stars. He states as his "Bottom Line" conclusion "Comodo System Utilities is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps".<ref name=PCMag.com>{{cite web|title=Comodo System Utilities Review|url=http://www.pcmag.com/article2/0,2817,2370702,00.asp}}</ref>

In 2013 Comodo System Utilities was rebranded as Comodo PC TuneUP.
In October 2013, PCMag gave PC TuneUp an Editor's rating of "Good". Jeffery Sacks wrote "Comodo PC Tuneup is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps."<ref>http://www.pcmag.com/article2/0,2817,2370702,00.asp</ref>

===Comodo Dragon Web Browser===
{{Main|Comodo Dragon (web browser)}}
On June 17, 2010 a cNET Editor's review gave the Comodo Dragon a 5 of 5 star score and a rating of Spectacular. they concluded "Dragon is not only fast, but like Google Chrome, it is not strewn with numerous icons, leaving more room for Web viewing. For those who are extra cautious about their online security, or for those who are worried about Google's data-mining, this fast browser is a great choice.
<ref>{{cite web|author=From Comodo: |url=http://download.cnet.com/Comodo-Dragon/3000-2356_4-75119680.html |title=Comodo Dragon - CNET Download.com |publisher=Download.cnet.com |date= |accessdate=2013-06-11}}</ref>

== Industry affiliations ==
Comodo is a member of the following industry organizations:
* [[Certificate Authority Security Council]] (CASC): In February 2013, Comodo became a founding member of this industry advocacy organization dedicated to addressing industry issues and educating the public on internet security.<ref>http://www.networkworld.com/news/2013/021413-council-digital-certificate-266728.html</ref><ref>http://www.darkreading.com/authentication/167901072/security/news/240148546/major-certificate-authorities-unite-in-the-name-of-ssl-security.html</ref>
* [[Common Computing Security Standards Forum]](CCSF): In 2009 Comodo was a founding member of the CCSF, an industry organization that promotes industry standards that protect end users. Comodo CEO Melih Abdulhayoğlu is considered the founder of the CCSF.<ref>http://www.securitypark.co.uk/</ref>
* [[CA/Browser Forum]]: In 2005, Comodo was a founding member of a new consortium of Certificate Authorities and web browser vendors dedicated to promoting industry standards and baseline requirements for internet security.<ref>{{cite web | url=https://www.cabforum.org/ | title=CA/Browser Forum | accessdate=2013-04-23}}</ref><ref>{{cite web | url=http://docbox.etsi.org/workshop/2012/201201_CA_DAY/5_Wilson_CAB-Forum.pdf | title=CA/Browser Forum History | last = Wilson | first = Wilson | publisher = DigiCert | accessdate=2013-04-23}}</ref>

==2011 breach incident==
On March 15, 2011, Comodo reported that a user account with an affiliate registration authority had been compromised which was used to create a new user account that issued nine [[certificate signing request]]s.<ref name="comodo inc1">{{cite web|title=Report of incident on 15-MAR-2011|url=https://www.comodo.com/Comodo-Fraud-Incident-2011-03-23.html|accessdate=2011-03-24|publisher=Comodo group}}</ref> Nine certificates for seven domains were issued.<ref name="comodo inc1"/> Comodo responded by revoking the nine certificates.<ref name="comodo inc1"/> Microsoft also issued a security advisory and update to address the issue.<ref>{{cite web|title=Microsoft Security Advisory (2524375)|url=http://www.microsoft.com/technet/security/advisory/2524375.mspx|date=March 23, 2011|accessdate=2011-03-24|format=Microsoft}}</ref><ref>{{cite web|title=Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing|url=http://support.microsoft.com/kb/2524375|date=March 23, 2011|accessdate=2011-03-24|work=Microsoft}}</ref>

The attack was traced to IP address 212.95.136.18, which originates in Tehran, Iran.<ref name="comodo inc1"/> Though Comodo initially reported the breach was the result of a "state-driven attack", it subsequently stated that the origin of the attack may be the "result of an attacker attempting to lay a false trail."<ref name="comodo inc1"/><ref name="comodo blog1">{{cite web|title=The Recent RA Compromise|url=http://blogs.comodo.com/it-security/data-security/the-recent-ca-compromise/|first=Phillip|last= Hallam-Baker|date=March 23, 2011 |accessdate=2011-03-24|publisher=Comodo Blog}}</ref> The issue, however, led to criticism of how certificates are issued and revoked.<ref>{{cite web|title=Iranian hackers obtain fraudulent HTTPS certificates: How close to a Web security meltdown did we get?|url=https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https|first=Peter |last=Eckersley|date=March 23, 2011|accessdate=2011-03-24|work=EFF}}</ref><ref>{{cite news|title=Iran accused in 'dire' net security attack|url=http://www.bbc.co.uk/news/technology-12847072|date=March 24, 2011|format=BBC|accessdate=2011-03-24|work=BBC News}}</ref><ref>{{cite web|title=Detecting Certificate Authority compromises and web browser collusion |url=https://blog.torproject.org/blog/detecting-certificate-authority-compromises-and-web-browser-collusion|date=March 22, 2011|accessdate=2011-03-24|work=TOR}}</ref><ref>{{cite news|title=Google, Yahoo, Skype targeted in attack linked to Iran|url=http://news.cnet.com/8301-31921_3-20046340-281.html|date=March 23, 2011|author1=Elinor Mills |author2=Declan McCullagh|work=CNET|accessdate=2011-03-24}}</ref>

On March 26, 2011, a person under the username "ComodoHacker" made several posts to Pastebin.com claiming to be an Iranian responsible for the attack against Comodo.<ref>{{cite news|title=Independent Iranian Hacker Claims Responsibility for Comodo Hack|url=http://www.wired.com/threatlevel/2011/03/comodo_hack/|first=Peter |last=Bright|date=March 28, 2011|format=WIRED|accessdate=2011-03-29|work=Wired}}</ref><ref>{{cite web|title=ComodoHacker's Pastebin|url=http://pastebin.com/u/ComodoHacker}}</ref> In September 2011, the same hacker claimed attacks against four other CAs, including [[DigiNotar]], which closed in the aftermath.<Ref>http://www.pcworld.idg.com.au/article/399812/comodo_hacker_claims_credit_diginotar_attack/</ref>

==References==
{{reflist|30em}}

==External links==
* {{Official website|www.comodo.com}}
* [http://www.antivirus.comodo.com Comodo Antivirus]

[[Category:Companies established in 1998]]
[[Category:Certificate authorities]]
[[Category:Computer security software companies]]
[[Category:Computer companies of the United States]]
[[Category:Comodo Group| ]]

Comodo Group

2014-01-23T02:33:36Z

Someone not using his real name: /* 2011 breach incident */

{{Infobox company
| name = Comodo Group, Inc.
| logo = [[File:Comodo logo.png]]
| type = [[Privately held company|Private]]
| company_slogan = Creating Trust
| foundation = [[United Kingdom]] ({{Start date|1998}}){{Citation needed|date=June 2013}}
| location_city = [[Clifton, New Jersey]]
| location_country = [[United States]]
| key_people = [[Melih Abdulhayoğlu]] ([[President]] and [[Chief executive officer|CEO]])
| num_employees = 1,100+
| industry = [[Computer security]], [[internet security]]
| products = {{Plainlist|
* Comodo Backup
* Comodo Cloud (cCloud)
* [[Comodo Endpoint Security Manager]]
* [[Comodo Internet Security]]
* Comodo HackerGuardian
* [[Comodo Mobile Security]]
* Comodo PC TuneUp
* [[Comodo SecureDNS]]
* Comodo SecureEmail
* [[Comodo SSL]]
* Comodo Web Inspector
* [[Comodo Dragon]]
* [[Comodo IceDragon]]
}}
| homepage = {{URL|www.comodo.com}}
}}
'''Comodo Group, Inc.''' is a privately held group of companies providing [[computer software]] and [[Transport Layer Security|SSL]] [[digital certificate]]s, based in [[Clifton, New Jersey]], [[United States]]. It has offices in the United Kingdom, Ukraine, Romania, China, India, Turkey and the United States.<ref name="comodoFactSheet">{{cite web|url=http://www.comodo.com/about/fact-sheet.php |title=Fact Sheet of Comodo Company - Creating Trust and Assurance - Comodo|publisher=comodo.com |date= |accessdate=2013-07-06}}</ref>

Comodo is the second most used [[certificate authority]] according to [[W3Techs]],<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage of SSL certificate authorities for websites |publisher=W3Techs.com |accessdate=October 19, 2013}}</ref> competing against [[Symantec]], [[Trend Micro]], [[DigiCert]], [[Entrust]], [[GlobalSign]], [[Go Daddy]], and others.

Comodo competes in the [[antivirus]] industry against [[Avira]], [[BullGuard]], [[F-Secure]], [[FRISK Software International|Frisk]], [[Kaspersky]], [[McAfee]], [[Panda Security]], [[Sophos]], [[Symantec]] and [[Trend Micro]] among [[List of antivirus software|others]].

==History==
The company was founded in 1998 in the United Kingdom, by Comodo CEO, [[Melih Abdulhayoğlu]], a technologist and an entrepreneur. Comodo relocated to the United States, first settling in [[Jersey City, New Jersey|Jersey City]], New Jersey in 2004. Comodo's product line is focused primarily on computer and internet security.<ref>{{cite news|last=Richmond|first=Riva|title=An Attack Sheds Light on Internet Security Holes|url=http://www.nytimes.com/2011/04/07/technology/07hack.html?_r=0|work=[[The New York Times]]|accessdate=17 March 2013|date=6 April 2011}}</ref> The firm operates a Certificate Authority that issues SSL certificates, offers a computer security suite that includes antivirus and firewall protection and offers other web and network protection services.

In December 2012 the company relocated its world headquarters from Jersey City to [[Clifton,_New_Jersey|Clifton]], New Jersey.<ref name="expressupdateusa1">{{cite web|url=http://listings.expressupdateusa.com/Business/NJ/Clifton/Comodo-Group-Inc/2019630004 |title=Comodo Group Inc - Clifton, NJ 07013 - (201) 963-0004 - Express Update Listing |publisher=Listings.expressupdateusa.com |date= |accessdate=2013-06-11}}</ref>

==Products==

===Certificate Authority===
{{Main|Comodo SSL}}
Comodo's largest and most prominent business is as a Certificate Authority that sells SSL Certificates. As of June 1, 2013 the company had a 27% Market Share among Certificate Authorities, just second behind Symantec, according to W3Tech.com<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage Statistics and Market Share of SSL Certificate Authorities for Websites, June 2013 |publisher=W3techs.com |date= |accessdate=2013-06-11}}</ref>

===Enterprise Products===
The Comodo strategy for the Enterprise market focuses primarily on cross selling web site PCI and Malware scanning services to their customers for SSL Certificates. They also market an End Point Security Management System that leverages their internet security software.

===Consumer Products===
The Comodo strategy for the consumer market is to offer its software products as [[freemium]]; that is, they are available for download free of charge,<ref>{{cite web
|url = http://www.techsupportalert.com/content/best-free-vista-64-bit-software.htm
|title = Best Free Windows 7 / Vista 64-bit Software
|work = Gizmo's Freeware
|date = 2 December 2010
|accessdate = 25 December 2010
}}</ref> but additional features and support are available for a fee.<ref name="tha-list">[http://www.comodo.com/products/comodo-products.php Products and Solutions]</ref> Among Comodo's free products is the [[Comodo Internet Security]], incorporating a [[personal firewall]], [[Host-based intrusion detection system]] and [[antivirus program]].<ref>{{cite web
|url = http://www.matousec.com/projects/proactive-security-challenge/results.php
|title = Proactive Security Challenge: Results and comments
|work = matousec.com
|publisher = Difinex Ltd
|accessdate = 25 December 2010
}}</ref> Other Comodo branded freeware security tools include an anti-malware tool, and a memory firewall that protects against over 90% of [[buffer overflow]] attacks.<ref>{{cite web
|url = http://www.techmixer.com/prevent-buffer-overflow-attack-with-comodo-memory-firewall/
|title = Prevent Buffer Overflow Attack with Comodo Memory Firewall
|work = TechMixer
|date = 26 September 2008 
|accessdate = 25 December 2010
}}</ref> For an additional fee, Comodo product users can subscribe to Comodo's computer cleaning and optimizing services for real-time computer assistance. Comodo also offers Comodo System Cleaner, which includes a free registry cleaner program,<ref>{{cite web
|url = http://www.pcworld.idg.com.au/index.php/taxid;2109929404;pid;7064;pt;1
|title = Comodo Registry Cleaner (PCWorld)
|work = [[PC World (magazine)|PC World Australia]]
|publisher = [[IDG Communications]]
|date = 2 December 2008
|last = Gralla
|first = Preston
|accessdate = 25 December 2010
}}</ref>

Comodo SecureEmail is an email encryption program that allows S/MIME email users to send emails to any email user without exchanging keys beforehand.
To support the mobile computing market Comodo has introduce the [[Comodo Mobile Security]] for the Android and Comodo Cloud storage for the Android and iOS.<ref>http://www.pcadvisor.co.uk/downloads/3329340/comodo-cloud-for-ios-and-android-20/</ref>

==Reception==

===Comodo Internet Security===
{{Main|Comodo Internet Security}}
Comodo Internet Security initially received mixed reviews; it was generally praised for its firewall and its value for price, but criticized for its poor antivirus detection. Over time, however, its antivirus component received better reviews. For instance, a 2008 review of Internet Security 3.5 from ''[[PC Magazine]]'' security analyst, Neil J. Rubenking, yielded a score of 2.5 out of 5, praising the suite's firewall and criticizing its antimalware component.<ref>{{cite journal|last=Rubenking,|first=Neil J.|title=Comodo Internet Security 3.5|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|date=3 November 2008|url=http://www.pcmag.com/article2/0,2817,2333803,00.asp|accessdate=7 March 2012}}</ref> Five years later, on 7 February 2013, Comodo Internet Security 2013 earned the ''PC Magazine'' Editor's Choice award. Neil J. Reubenking, reviewing the suite once again, gave it a score 4.5 of 5 stars.<ref name="Rubenking">{{cite web | url=http://www.pcmag.com/article2/0,2817,2415202,00.asp | title=Comodo Internet Security Complete 2013 | publisher=[[Ziff Davis]] | work=[[PC Magazine]] | date=7 February 2013 | accessdate=25 April 2013 | last=Rubenking | first=Neil J.}}</ref>

In response to [[Symantec]]'s comment over the effectiveness of free Antivirus software, on September 18, 2010, the CEO of Comodo Group [[Melih Abdulhayoğlu]] challenged Symantec to see which products can defend the consumer better against [[malware]].<ref>{{cite web
|url = http://www.melih.com/2010/09/18/challenge-to-symantec-from-comodo-ceo/
|title = Challenge to Symantec from Comodo CEO!
|first = Melih
|last = Abdulhayoğlu
|authorlink = Melih Abdulhayoğlu
|date = 18 September 2010
|publisher = Comodo Group
|accessdate = 22 September 2010
}}</ref> Symantec responded saying that if Comodo is interested they should have their product included in tests by independent reviewers.<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369524,00.asp
|title = Comodo Challenges Symantec to Antivirus Showdown
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 22 September 2010
|accessdate = 22 September 2010
}}</ref> On 29 September 2010, Neil J. Rubenking, the lead analyst for security of PC Magazine, published an article on Comodo Antivirus 5.0 that<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369897,00.asp
|title = Comodo Antivirus 5.0
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date=29 September 2010
|accessdate=29 September 2010
}}</ref><ref>{{cite news
|url = http://www.pcmag.com/image_popup/0,1871,iid=270708,00.asp
|title = Comodo Antivirus 5.0 malware blocking chart
|first = Neil J. Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 29 September 2010
|accessdate=29 September 2010
}}</ref> concluded that Comodo Antivirus 5.0 blocked a higher percentage of malware than Norton AntiVirus, but was less effective than the Norton solution when it came to malware removal. Rubenking's review also noted that the Comodo malware blocking gave a number of false positives which he felt tarnished Comodo's results.

In a 9 January 2013 review, ''Techworld'' awarded Comodo Internet Security Pro 2013 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."<ref>{{cite web | url=http://download.techworld.com/3328878/comodo-internet-security-pro-2013-v60/ | title=Comodo Internet Security Pro 2013 (v6.1) | publisher=[[IDG]] | work=TechWorld | date=9 January 2013 | accessdate=25 April 2013}}</ref> Also on the same date, Mike Williams of ''BetaNews.com'' reviewed Comodo Internet Security Pro 2013 and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."<ref>{{cite web | url=http://betanews.com/2013/01/09/comodo-internet-security-pro-2013-review/ | title=Comodo Internet Security Pro 2013 [Review] | work=BetaNews | date=9 January 2013 | accessdate=25 April 2013 | first=Mike | last=Williams}}</ref>

On 7 February 2013, Comodo Internet Security Complete v6 earned the ''PC Magazine'' Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score 4.5 of 5 stars, commended its support service, VPN solution, DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete 2013 isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."<ref name="Rubenking"/>

In October 2013, TopTenReviews.com reviewed the Comodo Internet Security 2014 Complete edition and gave it a score of 9.18 out of 10. Their review notes that the firewall component is their Gold Award winner for best firewall protection. However, they also comment on the lack of brand name recognition for Comodo's product.<ref>http://personal-firewall-software-review.toptenreviews.com/comodo-internet-security-pro-review.html</ref>

===Comodo PC TuneUp===
{{Main|Comodo System Utilities}}
In August 2012, Jeffery L. Wilson of PCMag.com gave Comodo System Utilities an Excellent rating, 4 of 5 stars. He states as his "Bottom Line" conclusion "Comodo System Utilities is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps".<ref name=PCMag.com>{{cite web|title=Comodo System Utilities Review|url=http://www.pcmag.com/article2/0,2817,2370702,00.asp}}</ref>

In 2013 Comodo System Utilities was rebranded as Comodo PC TuneUP.
In October 2013, PCMag gave PC TuneUp an Editor's rating of "Good". Jeffery Sacks wrote "Comodo PC Tuneup is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps."<ref>http://www.pcmag.com/article2/0,2817,2370702,00.asp</ref>

===Comodo Dragon Web Browser===
{{Main|Comodo Dragon (web browser)}}
On June 17, 2010 a cNET Editor's review gave the Comodo Dragon a 5 of 5 star score and a rating of Spectacular. they concluded "Dragon is not only fast, but like Google Chrome, it is not strewn with numerous icons, leaving more room for Web viewing. For those who are extra cautious about their online security, or for those who are worried about Google's data-mining, this fast browser is a great choice.
<ref>{{cite web|author=From Comodo: |url=http://download.cnet.com/Comodo-Dragon/3000-2356_4-75119680.html |title=Comodo Dragon - CNET Download.com |publisher=Download.cnet.com |date= |accessdate=2013-06-11}}</ref>

== Industry affiliations ==
Comodo is a member of the following industry organizations:
* [[Certificate Authority Security Council]] (CASC): In February 2013, Comodo became a founding member of this industry advocacy organization dedicated to addressing industry issues and educating the public on internet security.<ref>http://www.networkworld.com/news/2013/021413-council-digital-certificate-266728.html</ref><ref>http://www.darkreading.com/authentication/167901072/security/news/240148546/major-certificate-authorities-unite-in-the-name-of-ssl-security.html</ref>
* [[Common Computing Security Standards Forum]](CCSF): In 2009 Comodo was a founding member of the CCSF, an industry organization that promotes industry standards that protect end users. Comodo CEO Melih Abdulhayoğlu is considered the founder of the CCSF.<ref>http://www.securitypark.co.uk/</ref>
* [[CA/Browser Forum]]: In 2005, Comodo was a founding member of a new consortium of Certificate Authorities and web browser vendors dedicated to promoting industry standards and baseline requirements for internet security.<ref>{{cite web | url=https://www.cabforum.org/ | title=CA/Browser Forum | accessdate=2013-04-23}}</ref><ref>{{cite web | url=http://docbox.etsi.org/workshop/2012/201201_CA_DAY/5_Wilson_CAB-Forum.pdf | title=CA/Browser Forum History | last = Wilson | first = Wilson | publisher = DigiCert | accessdate=2013-04-23}}</ref>

==2011 breach incident==
On March 15, 2011, Comodo reported that a user account with an affiliate registration authority had been compromised which was used to create a new user account that issued nine [[certificate signing request]]s.<ref name="comodo inc1">{{cite web|title=Report of incident on 15-MAR-2011|url=https://www.comodo.com/Comodo-Fraud-Incident-2011-03-23.html|accessdate=2011-03-24|publisher=Comodo group}}</ref> Nine certificates for seven domains were issued.<ref name="comodo inc1"/> Comodo responded by revoking the nine certificates.<ref name="comodo inc1"/> Microsoft also issued a security advisory and update to address the issue.<ref>{{cite web|title=Microsoft Security Advisory (2524375)|url=http://www.microsoft.com/technet/security/advisory/2524375.mspx|date=March 23, 2011|accessdate=2011-03-24|format=Microsoft}}</ref><ref>{{cite web|title=Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing|url=http://support.microsoft.com/kb/2524375|date=March 23, 2011|accessdate=2011-03-24|work=Microsoft}}</ref>

The attack was traced to IP address 212.95.136.18, which originates in Tehran, Iran.<ref name="comodo inc1"/> Though Comodo initially reported the breach was the result of a "state-driven attack", it subsequently stated that the origin of the attack may be the "result of an attacker attempting to lay a false trail."<ref name="comodo inc1"/><ref name="comodo blog1">{{cite web|title=The Recent RA Compromise|url=http://blogs.comodo.com/it-security/data-security/the-recent-ca-compromise/|first=Phillip|last= Hallam-Baker|date=March 23, 2011 |accessdate=2011-03-24|publisher=Comodo Blog}}</ref> The issue, however, led to criticism of how certificates are issued and revoked.<ref>{{cite web|title=Iranian hackers obtain fraudulent HTTPS certificates: How close to a Web security meltdown did we get?|url=https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https|first=Peter |last=Eckersley|date=March 23, 2011|accessdate=2011-03-24|work=EFF}}</ref><ref>{{cite news|title=Iran accused in 'dire' net security attack|url=http://www.bbc.co.uk/news/technology-12847072|date=March 24, 2011|format=BBC|accessdate=2011-03-24|work=BBC News}}</ref><ref>{{cite web|title=Detecting Certificate Authority compromises and web browser collusion |url=https://blog.torproject.org/blog/detecting-certificate-authority-compromises-and-web-browser-collusion|date=March 22, 2011|accessdate=2011-03-24|work=TOR}}</ref><ref>{{cite news|title=Google, Yahoo, Skype targeted in attack linked to Iran|url=http://news.cnet.com/8301-31921_3-20046340-281.html|date=March 23, 2011|author1=Elinor Mills |author2=Declan McCullagh|work=CNET|accessdate=2011-03-24}}</ref>

On March 26, 2011, a person under the username "ComodoHacker" made several posts to Pastebin.com claiming to be an Iranian responsible for the attack against Comodo,<ref>{{cite news|title=Independent Iranian Hacker Claims Responsibility for Comodo Hack|url=http://www.wired.com/threatlevel/2011/03/comodo_hack/|first=Peter |last=Bright|date=March 28, 2011|format=WIRED|accessdate=2011-03-29|work=Wired}}</ref><ref>{{cite web|title=ComodoHacker's Pastebin|url=http://pastebin.com/u/ComodoHacker}}</ref> and later against four other CAs, including [[DigiNotar]], which closed in the aftermath.<Ref>http://www.pcworld.idg.com.au/article/399812/comodo_hacker_claims_credit_diginotar_attack/</ref>

==References==
{{reflist|30em}}

==External links==
* {{Official website|www.comodo.com}}
* [http://www.antivirus.comodo.com Comodo Antivirus]

[[Category:Companies established in 1998]]
[[Category:Certificate authorities]]
[[Category:Computer security software companies]]
[[Category:Computer companies of the United States]]
[[Category:Comodo Group| ]]

Comodo Group

2014-01-23T02:17:17Z

Someone not using his real name: /* 2011 breach incident */

{{Infobox company
| name = Comodo Group, Inc.
| logo = [[File:Comodo logo.png]]
| type = [[Privately held company|Private]]
| company_slogan = Creating Trust
| foundation = [[United Kingdom]] ({{Start date|1998}}){{Citation needed|date=June 2013}}
| location_city = [[Clifton, New Jersey]]
| location_country = [[United States]]
| key_people = [[Melih Abdulhayoğlu]] ([[President]] and [[Chief executive officer|CEO]])
| num_employees = 1,100+
| industry = [[Computer security]], [[internet security]]
| products = {{Plainlist|
* Comodo Backup
* Comodo Cloud (cCloud)
* [[Comodo Endpoint Security Manager]]
* [[Comodo Internet Security]]
* Comodo HackerGuardian
* [[Comodo Mobile Security]]
* Comodo PC TuneUp
* [[Comodo SecureDNS]]
* Comodo SecureEmail
* [[Comodo SSL]]
* Comodo Web Inspector
* [[Comodo Dragon]]
* [[Comodo IceDragon]]
}}
| homepage = {{URL|www.comodo.com}}
}}
'''Comodo Group, Inc.''' is a privately held group of companies providing [[computer software]] and [[Transport Layer Security|SSL]] [[digital certificate]]s, based in [[Clifton, New Jersey]], [[United States]]. It has offices in the United Kingdom, Ukraine, Romania, China, India, Turkey and the United States.<ref name="comodoFactSheet">{{cite web|url=http://www.comodo.com/about/fact-sheet.php |title=Fact Sheet of Comodo Company - Creating Trust and Assurance - Comodo|publisher=comodo.com |date= |accessdate=2013-07-06}}</ref>

Comodo is the second most used [[certificate authority]] according to [[W3Techs]],<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage of SSL certificate authorities for websites |publisher=W3Techs.com |accessdate=October 19, 2013}}</ref> competing against [[Symantec]], [[Trend Micro]], [[DigiCert]], [[Entrust]], [[GlobalSign]], [[Go Daddy]], and others.

Comodo competes in the [[antivirus]] industry against [[Avira]], [[BullGuard]], [[F-Secure]], [[FRISK Software International|Frisk]], [[Kaspersky]], [[McAfee]], [[Panda Security]], [[Sophos]], [[Symantec]] and [[Trend Micro]] among [[List of antivirus software|others]].

==History==
The company was founded in 1998 in the United Kingdom, by Comodo CEO, [[Melih Abdulhayoğlu]], a technologist and an entrepreneur. Comodo relocated to the United States, first settling in [[Jersey City, New Jersey|Jersey City]], New Jersey in 2004. Comodo's product line is focused primarily on computer and internet security.<ref>{{cite news|last=Richmond|first=Riva|title=An Attack Sheds Light on Internet Security Holes|url=http://www.nytimes.com/2011/04/07/technology/07hack.html?_r=0|work=[[The New York Times]]|accessdate=17 March 2013|date=6 April 2011}}</ref> The firm operates a Certificate Authority that issues SSL certificates, offers a computer security suite that includes antivirus and firewall protection and offers other web and network protection services.

In December 2012 the company relocated its world headquarters from Jersey City to [[Clifton,_New_Jersey|Clifton]], New Jersey.<ref name="expressupdateusa1">{{cite web|url=http://listings.expressupdateusa.com/Business/NJ/Clifton/Comodo-Group-Inc/2019630004 |title=Comodo Group Inc - Clifton, NJ 07013 - (201) 963-0004 - Express Update Listing |publisher=Listings.expressupdateusa.com |date= |accessdate=2013-06-11}}</ref>

==Products==

===Certificate Authority===
{{Main|Comodo SSL}}
Comodo's largest and most prominent business is as a Certificate Authority that sells SSL Certificates. As of June 1, 2013 the company had a 27% Market Share among Certificate Authorities, just second behind Symantec, according to W3Tech.com<ref>{{cite web|url=http://w3techs.com/technologies/overview/ssl_certificate/all |title=Usage Statistics and Market Share of SSL Certificate Authorities for Websites, June 2013 |publisher=W3techs.com |date= |accessdate=2013-06-11}}</ref>

===Enterprise Products===
The Comodo strategy for the Enterprise market focuses primarily on cross selling web site PCI and Malware scanning services to their customers for SSL Certificates. They also market an End Point Security Management System that leverages their internet security software.

===Consumer Products===
The Comodo strategy for the consumer market is to offer its software products as [[freemium]]; that is, they are available for download free of charge,<ref>{{cite web
|url = http://www.techsupportalert.com/content/best-free-vista-64-bit-software.htm
|title = Best Free Windows 7 / Vista 64-bit Software
|work = Gizmo's Freeware
|date = 2 December 2010
|accessdate = 25 December 2010
}}</ref> but additional features and support are available for a fee.<ref name="tha-list">[http://www.comodo.com/products/comodo-products.php Products and Solutions]</ref> Among Comodo's free products is the [[Comodo Internet Security]], incorporating a [[personal firewall]], [[Host-based intrusion detection system]] and [[antivirus program]].<ref>{{cite web
|url = http://www.matousec.com/projects/proactive-security-challenge/results.php
|title = Proactive Security Challenge: Results and comments
|work = matousec.com
|publisher = Difinex Ltd
|accessdate = 25 December 2010
}}</ref> Other Comodo branded freeware security tools include an anti-malware tool, and a memory firewall that protects against over 90% of [[buffer overflow]] attacks.<ref>{{cite web
|url = http://www.techmixer.com/prevent-buffer-overflow-attack-with-comodo-memory-firewall/
|title = Prevent Buffer Overflow Attack with Comodo Memory Firewall
|work = TechMixer
|date = 26 September 2008 
|accessdate = 25 December 2010
}}</ref> For an additional fee, Comodo product users can subscribe to Comodo's computer cleaning and optimizing services for real-time computer assistance. Comodo also offers Comodo System Cleaner, which includes a free registry cleaner program,<ref>{{cite web
|url = http://www.pcworld.idg.com.au/index.php/taxid;2109929404;pid;7064;pt;1
|title = Comodo Registry Cleaner (PCWorld)
|work = [[PC World (magazine)|PC World Australia]]
|publisher = [[IDG Communications]]
|date = 2 December 2008
|last = Gralla
|first = Preston
|accessdate = 25 December 2010
}}</ref>

Comodo SecureEmail is an email encryption program that allows S/MIME email users to send emails to any email user without exchanging keys beforehand.
To support the mobile computing market Comodo has introduce the [[Comodo Mobile Security]] for the Android and Comodo Cloud storage for the Android and iOS.<ref>http://www.pcadvisor.co.uk/downloads/3329340/comodo-cloud-for-ios-and-android-20/</ref>

==Reception==

===Comodo Internet Security===
{{Main|Comodo Internet Security}}
Comodo Internet Security initially received mixed reviews; it was generally praised for its firewall and its value for price, but criticized for its poor antivirus detection. Over time, however, its antivirus component received better reviews. For instance, a 2008 review of Internet Security 3.5 from ''[[PC Magazine]]'' security analyst, Neil J. Rubenking, yielded a score of 2.5 out of 5, praising the suite's firewall and criticizing its antimalware component.<ref>{{cite journal|last=Rubenking,|first=Neil J.|title=Comodo Internet Security 3.5|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|date=3 November 2008|url=http://www.pcmag.com/article2/0,2817,2333803,00.asp|accessdate=7 March 2012}}</ref> Five years later, on 7 February 2013, Comodo Internet Security 2013 earned the ''PC Magazine'' Editor's Choice award. Neil J. Reubenking, reviewing the suite once again, gave it a score 4.5 of 5 stars.<ref name="Rubenking">{{cite web | url=http://www.pcmag.com/article2/0,2817,2415202,00.asp | title=Comodo Internet Security Complete 2013 | publisher=[[Ziff Davis]] | work=[[PC Magazine]] | date=7 February 2013 | accessdate=25 April 2013 | last=Rubenking | first=Neil J.}}</ref>

In response to [[Symantec]]'s comment over the effectiveness of free Antivirus software, on September 18, 2010, the CEO of Comodo Group [[Melih Abdulhayoğlu]] challenged Symantec to see which products can defend the consumer better against [[malware]].<ref>{{cite web
|url = http://www.melih.com/2010/09/18/challenge-to-symantec-from-comodo-ceo/
|title = Challenge to Symantec from Comodo CEO!
|first = Melih
|last = Abdulhayoğlu
|authorlink = Melih Abdulhayoğlu
|date = 18 September 2010
|publisher = Comodo Group
|accessdate = 22 September 2010
}}</ref> Symantec responded saying that if Comodo is interested they should have their product included in tests by independent reviewers.<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369524,00.asp
|title = Comodo Challenges Symantec to Antivirus Showdown
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 22 September 2010
|accessdate = 22 September 2010
}}</ref> On 29 September 2010, Neil J. Rubenking, the lead analyst for security of PC Magazine, published an article on Comodo Antivirus 5.0 that<ref>{{cite news
|url = http://www.pcmag.com/article2/0,2817,2369897,00.asp
|title = Comodo Antivirus 5.0
|first = Neil J.
|last = Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date=29 September 2010
|accessdate=29 September 2010
}}</ref><ref>{{cite news
|url = http://www.pcmag.com/image_popup/0,1871,iid=270708,00.asp
|title = Comodo Antivirus 5.0 malware blocking chart
|first = Neil J. Rubenking
|work = [[PC Magazine]]
|publisher = Ziff Davis, Inc.
|date = 29 September 2010
|accessdate=29 September 2010
}}</ref> concluded that Comodo Antivirus 5.0 blocked a higher percentage of malware than Norton AntiVirus, but was less effective than the Norton solution when it came to malware removal. Rubenking's review also noted that the Comodo malware blocking gave a number of false positives which he felt tarnished Comodo's results.

In a 9 January 2013 review, ''Techworld'' awarded Comodo Internet Security Pro 2013 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."<ref>{{cite web | url=http://download.techworld.com/3328878/comodo-internet-security-pro-2013-v60/ | title=Comodo Internet Security Pro 2013 (v6.1) | publisher=[[IDG]] | work=TechWorld | date=9 January 2013 | accessdate=25 April 2013}}</ref> Also on the same date, Mike Williams of ''BetaNews.com'' reviewed Comodo Internet Security Pro 2013 and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."<ref>{{cite web | url=http://betanews.com/2013/01/09/comodo-internet-security-pro-2013-review/ | title=Comodo Internet Security Pro 2013 [Review] | work=BetaNews | date=9 January 2013 | accessdate=25 April 2013 | first=Mike | last=Williams}}</ref>

On 7 February 2013, Comodo Internet Security Complete v6 earned the ''PC Magazine'' Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score 4.5 of 5 stars, commended its support service, VPN solution, DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete 2013 isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."<ref name="Rubenking"/>

In October 2013, TopTenReviews.com reviewed the Comodo Internet Security 2014 Complete edition and gave it a score of 9.18 out of 10. Their review notes that the firewall component is their Gold Award winner for best firewall protection. However, they also comment on the lack of brand name recognition for Comodo's product.<ref>http://personal-firewall-software-review.toptenreviews.com/comodo-internet-security-pro-review.html</ref>

===Comodo PC TuneUp===
{{Main|Comodo System Utilities}}
In August 2012, Jeffery L. Wilson of PCMag.com gave Comodo System Utilities an Excellent rating, 4 of 5 stars. He states as his "Bottom Line" conclusion "Comodo System Utilities is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps".<ref name=PCMag.com>{{cite web|title=Comodo System Utilities Review|url=http://www.pcmag.com/article2/0,2817,2370702,00.asp}}</ref>

In 2013 Comodo System Utilities was rebranded as Comodo PC TuneUP.
In October 2013, PCMag gave PC TuneUp an Editor's rating of "Good". Jeffery Sacks wrote "Comodo PC Tuneup is a free and effective system-enhancing utility that is as potent, if not more so in certain cases, as paid apps."<ref>http://www.pcmag.com/article2/0,2817,2370702,00.asp</ref>

===Comodo Dragon Web Browser===
{{Main|Comodo Dragon (web browser)}}
On June 17, 2010 a cNET Editor's review gave the Comodo Dragon a 5 of 5 star score and a rating of Spectacular. they concluded "Dragon is not only fast, but like Google Chrome, it is not strewn with numerous icons, leaving more room for Web viewing. For those who are extra cautious about their online security, or for those who are worried about Google's data-mining, this fast browser is a great choice.
<ref>{{cite web|author=From Comodo: |url=http://download.cnet.com/Comodo-Dragon/3000-2356_4-75119680.html |title=Comodo Dragon - CNET Download.com |publisher=Download.cnet.com |date= |accessdate=2013-06-11}}</ref>

== Industry affiliations ==
Comodo is a member of the following industry organizations:
* [[Certificate Authority Security Council]] (CASC): In February 2013, Comodo became a founding member of this industry advocacy organization dedicated to addressing industry issues and educating the public on internet security.<ref>http://www.networkworld.com/news/2013/021413-council-digital-certificate-266728.html</ref><ref>http://www.darkreading.com/authentication/167901072/security/news/240148546/major-certificate-authorities-unite-in-the-name-of-ssl-security.html</ref>
* [[Common Computing Security Standards Forum]](CCSF): In 2009 Comodo was a founding member of the CCSF, an industry organization that promotes industry standards that protect end users. Comodo CEO Melih Abdulhayoğlu is considered the founder of the CCSF.<ref>http://www.securitypark.co.uk/</ref>
* [[CA/Browser Forum]]: In 2005, Comodo was a founding member of a new consortium of Certificate Authorities and web browser vendors dedicated to promoting industry standards and baseline requirements for internet security.<ref>{{cite web | url=https://www.cabforum.org/ | title=CA/Browser Forum | accessdate=2013-04-23}}</ref><ref>{{cite web | url=http://docbox.etsi.org/workshop/2012/201201_CA_DAY/5_Wilson_CAB-Forum.pdf | title=CA/Browser Forum History | last = Wilson | first = Wilson | publisher = DigiCert | accessdate=2013-04-23}}</ref>

==2011 breach incident==
On March 15, 2011, Comodo reported that a user account with an affiliate registration authority had been compromised which was used to create a new user account that issued nine [[certificate signing request]]s.<ref name="comodo inc1">{{cite web|title=Report of incident on 15-MAR-2011|url=https://www.comodo.com/Comodo-Fraud-Incident-2011-03-23.html|accessdate=2011-03-24|publisher=Comodo group}}</ref> Nine certificates for seven domains were issued.<ref name="comodo inc1"/> Comodo responded by revoking the nine certificates.<ref name="comodo inc1"/> Microsoft also issued a security advisory and update to address the issue.<ref>{{cite web|title=Microsoft Security Advisory (2524375)|url=http://www.microsoft.com/technet/security/advisory/2524375.mspx|date=March 23, 2011|accessdate=2011-03-24|format=Microsoft}}</ref><ref>{{cite web|title=Microsoft Security Advisory: Fraudulent Digital Certificates could allow spoofing|url=http://support.microsoft.com/kb/2524375|date=March 23, 2011|accessdate=2011-03-24|work=Microsoft}}</ref>

The attack was traced to IP address 212.95.136.18, which originates in Tehran, Iran.<ref name="comodo inc1"/> Though Comodo initially reported the breach was the result of a "state-driven attack", it subsequently stated that the origin of the attack may be the "result of an attacker attempting to lay a false trail."<ref name="comodo inc1"/><ref name="comodo blog1">{{cite web|title=The Recent RA Compromise|url=http://blogs.comodo.com/it-security/data-security/the-recent-ca-compromise/|first=Phillip|last= Hallam-Baker|date=March 23, 2011 |accessdate=2011-03-24|publisher=Comodo Blog}}</ref> The issue, however, led to criticism of how certificates are issued and revoked.<ref>{{cite web|title=Iranian hackers obtain fraudulent HTTPS certificates: How close to a Web security meltdown did we get?|url=https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https|first=Peter |last=Eckersley|date=March 23, 2011|accessdate=2011-03-24|work=EFF}}</ref><ref>{{cite news|title=Iran accused in 'dire' net security attack|url=http://www.bbc.co.uk/news/technology-12847072|date=March 24, 2011|format=BBC|accessdate=2011-03-24|work=BBC News}}</ref><ref>{{cite web|title=Detecting Certificate Authority compromises and web browser collusion |url=https://blog.torproject.org/blog/detecting-certificate-authority-compromises-and-web-browser-collusion|date=March 22, 2011|accessdate=2011-03-24|work=TOR}}</ref><ref>{{cite news|title=Google, Yahoo, Skype targeted in attack linked to Iran|url=http://news.cnet.com/8301-31921_3-20046340-281.html|date=March 23, 2011|author1=Elinor Mills |author2=Declan McCullagh|work=CNET|accessdate=2011-03-24}}</ref>

On March 26, 2011, a person under the username "ComodoHacker" made several posts to Pastebin.com claiming to be an Iranian responsible for the attack against Comodo,<ref>{{cite news|title=Independent Iranian Hacker Claims Responsibility for Comodo Hack|url=http://www.wired.com/threatlevel/2011/03/comodo_hack/|first=Peter |last=Bright|date=March 28, 2011|format=WIRED|accessdate=2011-03-29|work=Wired}}</ref><ref>{{cite web|title=ComodoHacker's Pastebin|url=http://pastebin.com/u/ComodoHacker}}</ref> and later against four other CAs, including [[DigiNotar]].<Ref>http://www.pcworld.idg.com.au/article/399812/comodo_hacker_claims_credit_diginotar_attack/</ref>

==References==
{{reflist|30em}}

==External links==
* {{Official website|www.comodo.com}}
* [http://www.antivirus.comodo.com Comodo Antivirus]

[[Category:Companies established in 1998]]
[[Category:Certificate authorities]]
[[Category:Computer security software companies]]
[[Category:Computer companies of the United States]]
[[Category:Comodo Group| ]]

Archive Team

2013-12-09T01:55:57Z

Someone not using his real name: mention this too

'''Archive Team''' is a group dedicated to [[digital preservation|preserving digital]] history that was founded by [[Jason Scott Sadofsky|Jason Scott]] in 2009. Its primary focus is the copying and preservation of content housed by at-risk services. Some of its projects include the partial preservation of [[GeoCities]],<ref>{{cite web |url=http://www.wired.com/epicenter/2010/11/geocities-lives-on-as-massive-torrent-download/ |title=Geocities Lives On as Massive Torrent Download |first=Scott |last=Gilbertson |work=Wired |date=2010-11-01 |archiveurl=http://www.webcitation.org/6744WKAy2 |archivedate=2012-04-20 |deadurl=no}}</ref><ref>
{{cite web |url=http://www.theregister.co.uk/2009/04/28/geocities_preservation/ |title=Web 0.2 archivists save Geocities from deletion |first=Austin |last=Modine |work=TheRegister |date=2009-04-28 |archiveurl=http://www.webcitation.org/6744REJO8 |archivedate=2012-04-20 |deadurl=no}}
</ref> [[Yahoo! Video]], [[Google Video]], [[Splinder]], [[Friendster]], [[FortuneCity]],<ref>
{{cite web |url=https://www.pcworld.com/article/253672/the_archive_team_rescues_user_content_from_doomed_sites.html |title=The 'Archive Team' Rescues User Content From Doomed Sites |first=Mark |last=Sullivan |work=PCWorld |date=2012-04-13 |archiveurl=http://www.webcitation.org/67440lW4b |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.technologyreview.com/web/39317/ |title=Fire in the Library |first=Matt |last=Schwartz |work=TechnologyReview |month=January |year=2012 |archiveurl=http://www.webcitation.org/67448ktjF |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.onthemedia.org/2012/mar/23/archive-team/ |title=The Archive Team |first1=Bob |last1=Garfield |first2=Jason |last2=Scott |work=OnTheMedia |date=2012-03-23 |archiveurl=http://www.webcitation.org/6744EGM0q |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.techdirt.com/articles/20120410/23092818446/historic-archive-websites-january-18th-sopa-blackout.shtml |title=Historic Archive Of Websites From The January 18th SOPA Blackout |first=Mike |last=Masnick |work=TechDirt |date=2012-04-12 |archiveurl=http://www.webcitation.org/6744H24m0 |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.bbc.co.uk/programmes/p00przc2 |title=Click: The Archive Team - Jason Scott talks about his mission to salvage our digital heritage |first=Jason |last=Scott |work=BBC |date=2012-03-06 |archiveurl=http://www.webcitation.org/6744M5iYY |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.radionz.co.nz/national/programmes/thiswayup/audio/2511595/the-archive-team |title=The Archive Team |first1=Simon |last1=Morton |first2=Jason |last2=Scott |work=RadioNZ |date=2012-03-03 |archiveurl=http://www.webcitation.org/6744OwRU6 |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.cbc.ca/spark/2011/04/full-interview-jason-scott-on-online-video-and-digital-heritage/ |title=Full Interview: Jason Scott on online video and digital heritage |first=Dan |last=Misener |work=CBC |date=2011-04-29 |archiveurl=http://www.webcitation.org/6744TasTv |archivedate=2012-04-20 |deadurl=no}}
</ref><ref>
{{cite web |url=http://www.newscientist.com/article/dn20396-digital-legacy-amateur-heroes-of-online-heritage.html |title=Digital legacy: Amateur heroes of online heritage |first=Sumit |last=Paul-Choudhury |work=NewScientist |date=2011-05-06 |archiveurl= |archivedate= |deadurl=no}}
</ref> and the "[[Aaron Swartz]] Memorial JSTOR Liberator".<ref>http://arstechnica.com/tech-policy/2013/01/aaron-swartz-memorial-jstor-liberator-sets-public-domain-academic-articles-free/</ref> Archive Team also archives [[URL shortener]] services<ref>[http://urlte.am URLTE.AM] - url shortening was a fucking awful idea</ref> and [[wikis]]<ref>[https://code.google.com/p/wikiteam/ WikiTeam] - We archive wikis, from Wikipedia to tiniest wikis</ref> on a regular basis.

According to [[Jason Scott Sadofsky|Jason Scott]], "Archive Team was started out of anger and a feeling of powerlessness, this feeling that we were letting companies decide for us what was going to survive and what was going to die."<ref>{{cite web |url=http://www.youtube.com/watch?feature=player_detailpage&v=tJqZGRIwtxk#t=1242s |title=Open Source Bridge 2012 Keynote - Jason Scott}}</ref> Scott continues, "it's not our job to figure out what's valuable, to figure out what's meaningful. We work by three virtues: [[Rage (emotion)|rage]], [[paranoia]] and [[kleptomania]]."<ref>{{cite web |url=http://www.youtube.com/watch?feature=player_detailpage&v=tJqZGRIwtxk#t=703s |title=Open Source Bridge 2012 Keynote - Jason Scott}}</ref>

== See also ==
* [[Digital Dark Age]]
* [[Internet Archive]]
* [[Web archiving]]

== References ==
{{Reflist|2}}

== External links ==
* [http://www.archiveteam.org Official Web Site]
* [http://archive.org/details/archiveteam Archive Team collection] at Internet Archive
* {{Twitter|archiveteam}}
* {{YouTube|id=-2ZTmuX3cog|title=ARCHIVE TEAM: A Distributed Preservation of Service Attack}}

{{web-stub}}
[[Category:Conservation and restoration]]
[[Category:Organizations established in 2009]]
[[Category:Web archiving initiatives]]

Infanteriefahrzeug

2013-08-31T00:53:12Z

Someone not using his real name: /* siehe auch */ Tatschanka

'''Infanteriefahrzeuge ''' (If.) waren bespannte Fahrzeuge der ehemaligen deutschen [[Reichswehr]] und [[Wehrmacht]], die dort überwiegend in der [[Infanterie]] eingesetzt wurden. Sie dienten vornehmlich dem Transport von besonderen Waffen der Infanterie und deren Munition, z.B. [[Maschinengewehr]]e, Granatwerfer, Minenwerfer und Infanterie-Geschütze.

Dagegen wurden die [[Heeresfeldwagen|Heeresfahrzeuge]] allgemein in allen Waffengattungen genutzt.

Die Nummerierung der Infanteriefahrzeuge entstand in der späten Reichswehrzeit (ca. Ende der 1920er Jahre). Dabei wurde nur der vorhandene Fuhrpark nummeriert; Fahrzeuge, die zu diesem Zeitpunkt nicht mehr im Deutschen Heer genutzt wurden, erhielten keine Nummern mehr. Das Nummernsystem wurde später auch von der Wehrmacht fortgeführt.

Unterschieden werden dabei nach der Bauart:
* unbespannte Karren (Handkarren)
* bespannte Karren, meist einspännig gefahren
* mehrspännige Protzen (Vorderwagen), zum Ziehen von Geschützen oder Hinterwagen
* unbespannte Hinterwagen, zum Zug durch Protzen.

== Maschinengewehr-Handwagen ==
Im deutschen Heer wurden bei der Infanterie die Maschinengewehre beim Marsch auf bespannten Fahrzeugen (bzw. Tragtieren) mitgeführt. Wo die bespannten Fahrzeuge aufgrund des Geländes oder der feindlichen Waffenwirkung nicht mehr benutzt werden konnten, wurden zum Transport der leichten und schweren Maschinengewehre Handwagen verwendet.

=== Maschinengewehr-Handziehwagen ===
Bereits Anfang 1904 verfügte das 1. Seebataillon der Kriegsmarine in Deutsch-Südwest-Afrika über Handziehwagen für das ''schwere MG 03'', um seine Maschinengewehre nach Landungen von See auch ohne Pferde fortbewegen zu können. Ab 1912 wurden dann die Maschinengewehr-Züge aller drei Seebataillone mit Handziehwagen für das ''schwere MG 08'' ausgestattet. Während des 1. Weltkrieges wurden die Handziehwagen beim Deutschen Marinekorps in Flandern genutzt.

Der leer ca. 40 kg wiegende Karren transportierte das ''schwere MG 08'' auf ''Dreibein-Lafette'', 8 Patronenkästen zu je 250 Schuss Munition, einen ''Kühlwasserausgleicher'' und einen ''Werkzeugzubehörkasten''. Er wurde von 5 Mannschaften bewegt: Ein Mann führte den Karren an zwei langen, seitlich angebrachten Stangen, während die 4 anderen Mannschaften den Karren mit Hilfe von Zugseilen zogen.<ref>Fleischer: ''Bespannte Fahrzeuge des Deutschen Heeres bis 1945.'', S. 70</ref>

=== Handwagen für MG 08 und MG 08/15 ===
1926 beim ''Artillerie-Konstruktionsbüro Spandau'' entwickelt, wurde dieser leer ca. 60 kg wiegende und von 2 Mannschaften an einer Handdeichsel gezogene Handwagen ab 1917 bei der Truppe zum Transport der ''leichten MG08/15 auf Gabel-Lafette'' bzw. der ''schweren MG 08 auf Lafette'' verwandt. Er fasste neben dem Maschinengewehr 4 ''Patronenkästen 15'' und einen ''Tragekasten 16'' mit 2 ''Patronenkästen 16'' und weiteres Material.<ref>Fleischer: ''Bespannte Fahrzeuge des Deutschen Heeres bis 1945.'', S. 72</ref>

Die Schützen-Züge der Reichswehr waren mit je zwei leichten Maschinengewehre [[MG 08|MG 08/15 bzw. MG 08/18]] und zwei Handwagen ausgestattet. Beim Marsch wurden die Handwagen zu zweit nebeneinander an die als Gefechtswagen genutzten [[Heeresfeldwagen|leichten Heeresfeldwagen (Hf.1)]] angehängt. <ref>Hube: ''Der Infanterist.'' 1925, S. 425 und S. 436</ref>

Mit Umstellung auf die ''Einheitsgruppe'' (ca. 1930) wurden die Handwagen für das ''leichte MG 08/15'' offenbar nicht mehr benutzt, während die Handwagen für das ''schwere MG 08'' ab 1926 durch If.1 und If.2 abgelöst wurden.
Aber noch 1939 soll die SS-Heimwehr Danzig solche Handkarren zum Transport von ''8 cm Granatwerfern 34'' benutzt haben.<ref>Fleischer: ''Bespannte Fahrzeuge des Deutschen Heeres bis 1945.'', S. 72</ref>

=== Maschinengewehr-Handwagen für MG 08 mit Schlitten (If.1) oder Dreifuß (If.2) ===
Diese 1926 in die Reichswehr eingeführten Maschinengewehr-Handwagen dienten dem Transport des [[MG 08|schweren Maschinengewehrs 08]], für dass es zwei verschiedene Lafetten gab (den üblichen „Schlitten“ und den leichteren „Dreifuß“), des Zubehörs und der zugehörigen Munition. Bei den Maschinengewehr-Zügen der Reichswehr wurde je ein solcher Handwagen leer hinter dem Maschinengewehr-Wagen, schwer (If.3) angehängt. Bei Bedarf wurden die Maschinengewehre auf die Handwagen umgeladen.<ref>Hube: ''Der Infanterist.'' 1925, S. 827-830</ref>

<gallery>
Datei:Leichtes MG 08 15.jpg|Leichtes MG 08/15 beim Transport auf Handwagen
Datei:Bundesarchiv_Bild_102-06341,_Ostpreußen,_Herbstmanöver.jpg|MG-Handwagen (If.1) hinter schwerem MG-Wagen (If.3)
</gallery>

== Maschinengewehr-Wagen für MG 08 ==
Die mehrspännigen, pferdegezogenen Maschinengewehr-Wagen (M.G.W.) dienten der Verlastung der [[MG 08|schweren Maschinengewehre 08]] und der zugehörigen Munition der Maschinengewehr-Kompanien bei Märschen. Sie bestanden aus identischen Vorderwagen (Protzen) aber zwei verschiedenen Hinterwagen. Beide Wagen waren überwiegend aus Blech gefertigt und nutzten gewöhnliche, aus Holz gefertigte und mit einem eisernen Radreifen versehene „Feldwagenräder“. Der Vorderwagen hatte eine Stangendeichsel mit Hinterbracke, an der zwei Ortscheite zum Anschirren der beiden Stangenpferde befestigt waren (zweispänniger Zug). Die Deichsel wurde von den Stangenpferden mittels einer Steuerkette gehalten. Bei vierspännigen Zug wurden die zusätzlichen Vorderpferde mit Tauen an einer Vorderbracke angeschirrt, die dazu an der Spitze der Deichsel befestigt wurde.

=== Der Maschinengewehr-Wagen, schwer (If.3) für zwei MG 08 ===
==== Reichswehr ====
Diese Wagen wurden in der Reichswehr zunächst nur in den Maschinengewehr-Kompanien der Infanterie-Bataillone eingesetzt, nicht jedoch bei den Jäger-Bataillonen (jeweils ein Bataillon je Infanterie-Division<ref>Matuschka: ''Organisation des Reichsheeres.'' 1970, S. 320</ref>), die ihre Maschinengewehre auf Tragtieren mitführten<ref>''H.Dv. 130'', 1926, Bild 26, S. 9a</ref>).
In den ersten drei Zügen der Maschinengewehr-Kompanien wurden jeweils zwei dieser Fahrzeuge zweispännig gefahren („zwospännige Züge“,auch „Kampfzüge“). Die MG-Bedienungen (je ein Gewehrführer und vier Schützen) und der Zugtrupp (je ein Richtkreisunteroffizier, ein Meßmann und zwei Melder) marschierten zu Fuß. Lediglich die Fahrer vom Bock fuhren auf den Wagen und nur der Zugführer war beritten.
Da bei der Reichswehr die Maschinengewehr-Züge aber drei Maschinengewehre hatten, wurde auf dem jeweils ersten Wagen eines Zuges nur ein Maschinengewehr, auf dem zweiten Wagen aber zwei Maschinengewehre mitgeführt. Von jedem Wagen wurde zusätzlich ein Maschinengewehr-Handwagen (If.1 oder If.2) gezogen.<ref>Hube: ''Der Infanterist.'' 1925, S. 833-834</ref><ref group="A"> Das bedeutete aber, dass nur zwei der drei Maschinengewehre im Handzug transportiert werden konnten.</ref>

Ca. 1932 wurden die Züge unter Beibehalt der Anzahl von drei Maschinengewehren auf drei Wagen verstärkt, so dass nun nur noch ein Maschinengewehr je Wagen mitgeführt wurde. Neben den Fahrern vom Bock konnten nun auch die Gewehrführer auf die Vorderwagen aufsitzen. Der Zugtrupp, bestehend aus Richtkreisunteroffizier, Meßmann und einem Melder wurde beritten; der zweite Melder blieb jedoch unberitten. Auch die Anzahl der Handwagen wurden auf drei erhöht.<ref>''H.Dv. 130'', 1926, Deckblatt zu Bild 17, S. 61</ref><ref group="A">Damit konnten nun alle Maschinengewehre auch im Handzug mitgeführt werden.</ref>

Ca. 1934 wurden die „zwospännigen Züge“ auf jeweils vier Maschinengewehre gebracht und in zwei „Halbzüge“ zu je zwei Maschinengewehren und zwei Wagen eingeteilt.<ref>Queckbörner: ''Gefechtsunterricht-ABC.'', 1935, S. 5</ref> Zur Führung von zwei - auch getrennt voneinander eingesetzten - Halbzügen mussten die Zugtrupps verdoppelt werden. Allerdings gab es dann nur noch zwei „zwospännige“ Züge in den Maschinengewehr-Kompanien der Infanterie-Bataillone.<ref>''K.St.N. Nr. 151a'' vom 1. Oktober 1937</ref><ref>''K.St.N. Nr. 151b'' vom 1. Oktober 1937</ref>

==== Wehrmacht ====
Bei der [[Wehrmacht]] wurden die Maschinengewehr-Wagen, schwer im Allgemeinen so wie bei der Reichswehr eingesetzt, jedoch wurden bei den Maschinengewehr-Zügen die vier Maschinengewehre auf nur noch zwei Maschinengewehr-Wagen verlastet, also zwei Maschinengewehre auf jedem Wagen. Für den Transport von Munition wurden anstelle der anderen beiden Maschinengewehr-Wagen nun zwei [[Heeresfeldwagen|Heeresfahrzeuge 1 (Hf.1)]] als Munitionswagen eingesetzt. Ein Halbzug bestand nun aus jeweils einem Maschinengewehr-Wagen und einem Munitionswagen.<ref>''K.St.N. Nr. 151a'' vom 1. Oktober 1937</ref><ref>''K.St.N. Nr. 151b'' vom 1. Oktober 1937</ref>

Bei der [[Landwehr (Militär)#Deutsches Reich 1933 bis 1945|Landwehr]] gab es keine ausgewiesenen Maschinengewehr-Kompanien, jedoch wurde bei jeder Landwehr-Schützen-Kompanie ein in zwei Halbzüge teilbarer Maschinengewehr-Zug etatisiert. Diese Kompanien wurden deshalb auch als „gemischte“ Kompanien bezeichnet. Den Landwehr-Maschinengewehr-Zügen wurden jedoch keine Munitionswagen zugeteilt.<ref>''K.St.N. Nr. 131 (Lw)'' vom 1. Oktober 1937</ref>

Nach Einführung des [[MG 34]] auf Lafette als neues schweres Maschinengewehr ab 1936 wurden dann auch die Maschinengewehr-Wagen, schwer (If.3) abgelöst und durch die neuen Maschinengewehr-Wagen 36 (If.5) ersetzt.<ref>''K.St.N. Nr. 151a'' vom 1. Oktober 1937</ref><ref>''K.St.N. Nr. 151b'' vom 1. Oktober 1937</ref>

=== Der Maschinengewehr-Wagen, leicht (If.4) für ein MG 08 ===
==== Kaiserreich bzw. Erster Weltkrieg ====
Dieser Wagen entsprach dem seit Beginn des 20. Jahrhunderts im Kaiserlichen Heer genutzten Transportfahrzeug für Maschinengewehre, überwiegend dem [[MG 08|Maschinengewehr 08]]. 1912 wurde eine „leichtere“ Ausführung dieses Maschinengewehrwagens eingeführt. Außerdem wurden solche Wagen auch ohne Maschinengewehr als „Munitionswagen“ benutzt.<ref>Matuschka: ''Organisationsgeschichte des Heeres 1890-1918.'' 1968, S. 166</ref>

Vor und während des Ersten Weltkriegs bildeten je drei solche Wagen, zwei als Maschinengewehrwagen und einer als Munitionwagen, einen Maschinengewehr-Zug, drei solche Züge eine [[Maschinengewehr-Abteilung]].<ref>Merkatz: ''Unterrichtsbuch für die Maschinengewehr-Kompagnien. Gerät 08.'' 1917, S. 241</ref> Die Wagen wurden vierspännig gezogen und die komplette Bedienung des MG gefahren.
Damit wurde eine hohe Marschgeschwindigkeit und hohe täglich Marschleistung erzielt und konnten die so ausgestatteten Maschinengewehr-Abteilungen auch mit der Kavallerie zusammen eingesetzt werden.<ref>Matuschka: ''Organisationsgeschichte des Heeres 1890-1918.'' 1968, S. 166</ref>

1906 wurden Versuche durchgeführt, diese Wagen auch zweispännig zu fahren<ref>Matuschka: ''Organisationsgeschichte des Heeres 1890-1918.'' 1968, S. 166</ref>, hier mussten die Bedienungen der Maschinengewehre zu Fuß marschieren. Nur zwei Soldaten saßen je Wagen auf: ein Fahrer vom Bock und entweder ein Gewehrführer (auf Maschinengewehr-Wagen) bzw. ein Wagenführer (auf Munitionswagen).<ref>Merkatz: ''Unterrichtsbuch für die Maschinengewehr-Kompagnien. Gerät 08.'' 1917, S. 241</ref> Die nach diesem Muster aufgestellten Einheiten, nun ''Maschinengewehr-Kompanien'' genannt, erreichten nur noch die übliche Marschleistung der Infanterie.

==== Reichswehr ====
Bei den Infanterie-Bataillonen der Reichswehr wurden jeweils drei dieser Fahrzeuge vierspännig bei den mit je drei schweren [[MG 08]] ausgestatteten ''„Begleitzügen“'' (den jeweils vierten Zügen der Maschinengewehr-Kompanien) benutzt (die Jäger-Bataillone, jeweils ein Bataillon je Division<ref>Matuschka: ''Organisation des Reichsheeres.'' 1970, S. 320</ref>, hatten jedoch keine „Begleitzüge“<ref>''H.Dv. 130'', 1926, Bild 26, S. 9a</ref>). Reine Munitionswagen - wie im Ersten Weltkrieg - gab es nicht mehr. Auf die Hinterwagen saßen die Schützen 2 und Schützen 3 jedes Maschinengewehrs auf, auf die Vorderwagen die Schützen 1 und Schützen 4. Während der Zugführer, der Richtkreisunteroffizier und die Gewehrführer des 1. und 2. Maschinengewehrs ritten, saßen der Gewehrführer des 2. Maschinengewehrs, der Messmann und der Melder noch zusätzlich auf die Wagen auf. Dabei saß der Meßmann auf dem 1. Maschinengewehr-Wagen und der Melder auf dem 3. Maschinengewehr-Wagen, und zwar jeweils in der Mitte des Vorderwagens, wo sie von den beiden außen sitzenden Schützen untergehakt wurden. Der Gewehrführer des 2. Maschinengewehrs nahm jedoch den Platz des Schützen 3 auf dem Hinterwagen des 2. Maschinengewehr-Wagens ein, dieser nahm den Platz des Schützen 4 auf dem Vorderwagen ein, so dass der Schütze 4 nun in der Mitte des Vorderwagens zu sitzen kam und sich dort unterhakte.<ref>Hube: ''Der Infanterist.'' 1925, S. 834-838</ref>

1923 wurden bei den Reiter-Regimentern der Reichswehr dann auch je vier dieser Wagen bei den mit je vier schweren [[MG 08]] ausgestatteten Maschinengewehr-Zügen genutzt. Dabei wurde der Maschinengewehr-Zug in zwei „Halbzüge“ zu je zwei Maschinengewehren und zwei Wagen aufgeteilt. 1933 wurde dort die Anzahl der Maschinengewehre und Wagen auf je acht verdoppelt, die in vier Halbzüge eingeteilt waren.<ref>Matuschka: ''Organisation des Reichsheeres.'' 1970, S. 324</ref>

Ca. 1932 wurden bei „Begleitzügen“ der Maschinengewehr-Kompanien der Infanterie-Bataillone aus dem Zugtrupp auch der Meßmann und der Melder beritten, ebenso der Gewehrführer des 2. Maschinengewehrs. Die dadurch frei werden Plätze in der Mitte der drei Vorderwagen wurden jetzt besetzt durch einen zusätzlichen Melder (1. Maschinengewehr-Wagen), einen Reserveschützen (2. Maschinengewehr-Wagen) und einen Beschlagschmied (3. Maschinengewehr-Wagen).<ref>''H.Dv. 130'', 1926, Deckblatt zu Bild 18, S. 62</ref>

Ca. 1934 wurden auch die „Begleitzüge“ der Maschinengewehr-Kompanien der Infanterie-Bataillone in zwei Halbzüge zu je zwei Maschinengewehren und zwei Wagen umgegliedert.<ref>Queckbörner: ''Gefechtsunterricht-ABC.'', 1935, S. 5</ref> Zur Führung von zwei - auch getrennt voneinander eingesetzten - Halbzügen mussten die Zugtrupps verdoppelt werden.<ref>''K.St.N. Nr. 151a'' vom 1. Oktober 1937</ref><ref>''K.St.N. Nr. 151b'' vom 1. Oktober 1937</ref>

==== Wehrmacht ====
Von der Wehrmacht wurden die Wagen zunächst genau so wie schon in der Reichswehr weiter benutzt. Nach Einführung des [[MG 34]] auf Lafette als neues schweres Maschinengewehr ab 1936 wurden dann auch die Maschinengewehrwagen, leicht (IF.4) abgelöst. Dabei verschwanden bei der Infanterie die „Begleitzüge“ - sie gingen in „zwospännigen Kampfzügen“ auf.<ref>H.Dv. 130/3a (Entwurf) vom 24. August 1942, S. 124-125</ref> Bei der Kavallerie wurden die schweren Maschinengewehre MG 36 und die zugehörige Munition auf Packpferden verlastet.<ref>Richter: ''Die Feldgrauen Reiter.'', 1986, S.230-231</ref>

== Der Maschinengewehr-Wagen 36 (If.5) für zwei MG 34 ==
bei der Wehrmacht wurde als Nachfolger des Maschinengewehrwagen, schwer (If.3) zusammen mit den [MG 34] bei den Maschinengewehr-Kompanien der Infanterie-Bataillone der Maschinengewehr-Wagen 36 (If.5) eingeführt; nicht jedoch bei den Gebirgsjägern, die ihre Maschinengewehre - wie vorher die Jäger der Reichswehr - auf Tragtieren mitführten.
Wie sein Vorgänger war auch der neue Wagen aus Blech gefertigt und in einen zweirädrigen Vorderwagen und einen zweirädrigen Hinterwagen aufgeteilt, wobei der Hinterwagen zum Transport von zwei schweren Maschinengewehren MG 34 mit Maschinengewehr-Lafette 34 und der zugehörigen Munition diente.

Er wurde ebenfalls zweispänning gefahren, hatte jedoch luftgefüllte Stahlscheibenräder. Die Maschinengewehre wurden auch nicht mehr offen - und damit der Witterung ausgesetzt - transportiert, sondern wurden in verschließbaren Kästen aufbewahrt; die Lafetten wurden - mit Planen abgedeckt - außen an der Hinterwand des Hinterwagens befestigt.

Als besondere Neuheit konnten die beiden Maschinengewehre in eine „Zwillingssockel-Lafette“ auf dem Wagen fertig zur Fliegerabwehr transportiert werden. Dabei konnte auch einer der beiden Richtschütze in der Lafette auf dem Wagen mitfahren. Durch eine spezielle Vorrichtung konnte der Schütze den Hinterwagen vom Vorderwagen abkuppeln und gleichzeitig zwei Stützen ausfahren, die den Hinterwagen stabilisierten und so dem Schützen einen sicheren Stand zum Fliegerbeschuss gaben.

Ab 1941 wurde der Maschinengewehr-Wagen 36 (If.5) bei den „leichten“ Infanterie-Divisionen (den späteren Jäger-Dvisionen) durch zwei einspännige Kombinationen aus je zwei [[Infanteriekarren IF8|Infanterie-Karren (If.8)]] ersetzt. Im weiteren Kriegsverlauf, als die Zwillings-Maschinengewehre ihre Wirksam gegen die modernen Flugzeuge verloren hatten, wurde dies bei allen Divisionen vorgenommen.

<gallery>
Datei:Bundesarchiv Bild 146-2005-0176, Anschluss sudetendeutscher Gebiete.jpg|M.G.-Wagen 36 (If.5) zur Fliegerabwehr auf dem Marsch
</gallery>

== Verweise ==
=== siehe auch ===
* [[MG 08]]
* [[Maschinengewehr-Abteilung]]
* [[Heeresfeldwagen]]
* [[Infanteriekarren IF8]]
* [[Tatschanka]]

=== Literatur ===
* Heeresdienstvorschrift (H.Dv.) Nr. 130: ''Ausbildungsvorschrift für die Infanterie.'' Heft III, Druck und Verlag der Reichsdruckerei, Berlin 1926 (mit eingearbeiteten Deckblättern und Änderungen ohne Jahresangabe).
* Heeresdienstvorschrift (H.Dv.) Nr. 130/3a (Entwurf) vom 24. August 1942: ''Ausbildungsvorschrift für die Infanterie.'' Heft 3a, Verlag „Offene Worte“, Berlin ohne Jahresangabe.
* Wolfgang Fleischer: ''Deutsche Infanteriekarren, Heeresfeldwagen und Heeresschlitten 1900–1945.'' Waffen-Arsenal Band 153, Podzun-Pallas-Verlag 1995, ISBN 3790905380.
* Wolfgang Fleischer: ''Bespannte Fahrzeuge des Deutschen Heeres bis 1945." Aus der Reihe "Typenkompass", Motorbuch Verlag, 1. Auflage, Stuttgart 2011, ISBN 978-3-613-03290-3.
* Hube: ''Der Infanterist. Handbuch für Selbstunterricht und Ausbildung des jungen Frontsoldaten der Infanterie.'' Verlag "Offene Worte", Charlottenburg 1925.
* Edgar Graf von Matuschka: ''Organisationsgeschichte des Heeres 1890-1918.'' in: Militärgeschichtlichen Forschungsamt (Hrsg.): Deutsche Militärgeschichte in sechs Bänden 1648-1939, Pawlak Verlagsgesellschaft mbH, Herrsching 1983, ISBN 3-88199-112-3, Band 3, Abschnitt V (1968).
* Edgar Graf von Matuschka: ''Organisation des Reichsheeres.'' in: Militärgeschichtlichen Forschungsamt (Hrsg.): Deutsche Militärgeschichte in sechs Bänden 1648-1939, Pawlak Verlagsgesellschaft mbH, Herrsching 1983, ISBN 3-88199-112-3, Band 3, Abschnitt VI (1970).
* Friedrich von Merkatz (Hrsg.): ''Unterrichtsbuch für die Maschinengewehr-Kompagnien. Gerät 08.'' Verlag Eisenschmidt, 19. Auflage, Berlin 1917.
* Queckbörner: ''Gefechtsunterricht-ABC in Wort und Bild. Ein illustriertes Handbuch für den Unterricht in der Kaserne zur Unterstützung und Förderung der Gefechtsausbildung des Schützen (Für Lehrer und Schüler).'' Verlag Mittler & Sohn, Berlin 1935.
* Klaus Christian Richter: ''Die Feldgrauen Reiter. Die berittenen und bespannten Truppen in reichswehr und Wehrmacht.'' 1. Auflage, Motorbuch Verlag, Stuttgart 1986, ISBN 3-613-01100-X.

=== Weblinks ===
* ''[http://www.kfzderwehrmacht.de/Hauptseite_deutsch/Anhanger/Infanteriefahrzeuge/infanteriefahrzeuge.html Kfz. der Wehrmacht]'', eingesehen am 10. Juli 2012
* ''[http://www.wwiidaybyday.com/kstn/kstn151a1okt37.htm Kriegsstärkenachweisung (K.St.N.) Nr. 151a]'', eingesehen am 31. Juli 2012
* ''[http://www.wwiidaybyday.com/kstn/kstn151b1okt37.htm Kriegsstärkenachweisung (K.St.N.) Nr. 151b]'', eingesehen am 31. Juli 2012
* ''[http://www.wwiidaybyday.com/kstn/kstn131lw1okt37.htm Kriegsstärkenachweisung (K.St.N.) Nr. 131 (Landwehr)]'', eingesehen am 31. Juli 2012

=== Einzelnachweise ===
<references />

=== Anmerkungen ===
<references group="A"/>

[[Kategorie:Wehrmacht]]
[[Kategorie:Radfahrzeug der Wehrmacht]]

Tatschanka

2013-08-31T00:44:11Z

Someone not using his real name:

[[Datei:Tachanka Nova Kakhovka.jpg|miniatur|Das Monument der legendären Tatschanka in [[Kachowka]]]]
Eine '''Tatschanka''' ({{RuS|тачанка}}) ist ein mit einem schweren [[Maschinengewehr]] (MG) im Heck bewaffneter, von Pferden gezogener Kampfwagen, in der Regel einfache [[Kutsche]]n oder offene Wagen. Eine Tatschanka konnte von zwei, drei oder vier Pferden gezogen werden (siehe Bild des Malers Grekow „Die MGs rücken vor“, 1925). Die Besatzung bestand aus zwei oder drei Soldaten, der MG-Bedienung und einem Kutscher (er galt auch als Ersatzmann der Bedienung). Die Tatschanka wurde angeblich von [[Nestor Machno]] erfunden.

== Namensgebung ==
Eine andere Version besagt, dass es ein verkürztes Wort von „Tawritschanka“ ist, welches holprige Transporte in der [[Ukraine|Südukraine]] und auf der [[Krim]] bezeichnet, abgeleitet von dem regionalen Ausdruck „Taurida“. Später veränderte sich das Wort zu „Tatschanka“. Jedoch bezeichnet „Tawritschanka“ ein großes Fuhrwerk, ähnlich einem [[Leiterwagen]] mit einem hölzernen Wagenkasten, die Tatschanka dagegen hatte eine leichte Besatzung, keinen Aufbau und war gefedert. Das Vorhandensein einer Federung war grundlegend für die Geschwindigkeit bei Fahrten auf Feldwegen bzw. weglosen Flächen sowie für die Treffgenauigkeit beim Schießen.

Die Anhänger Nestor Machnos wiesen im Zusammenhang mit der Bezeichnung auf das ukrainische Wort ''netytschanka'' („нетичанка“), was einen leichten, gefederten Wagen bedeutete. Ihrer Meinung nach kam die Bezeichnung daher, dass die Achsen des Fahrgestells den Aufbau nicht berührten („нэ тыкалысь“ auf Ukrainisch).

Oleg N. Trubatschow und auch derzeitige Experten leiten die Bezeichnung ebenfalls aus dem ukrainischen „netytschanka“ ab, das vom polnischen Wort ''najtyczanka'' – einer Art von Vehikel / [[Kalesche]] – herrührt. Das polnische Wort wiederum stammt von dem deutschen Namen des Gebietes [[Neu-Titschein]] in [[Tschechien]] ab.

== Geschichte ==
Im [[Russischer Bürgerkrieg|Bürgerkrieg]] wurde die Tatschanka einerseits zur Truppenverlegung und zur Führung unerwarteter Schläge auf dem Gefechtsfeld verwendet. Besondere Popularität erhielt die Tatschanka bei den Anhängern Nestor Machnos. Letztere verwandten die Tatschanka nicht nur im Kampf, sondern auch zur Verlegung der [[Infanterie]]. Dabei entsprach die Marschgeschwindigkeit der [[Kavallerie]]truppen im Trab. Damit erreichten die Abteilungen Machnos leicht bis zu 100 km pro Tag und das über mehrere Tage in Folge. So schafften große Kräfte von Machno nach dem entscheidenden Durchbruch bei Peregonowka die Strecke von 600 km zwischen Umana bis Guljai-Polja in elf Tagen und nahmen überraschend Nachschubgarnisonen der [[Weiße Armee|Weißen]] ein.

Die Verwendung der Tatschanka erreichte ihren Höhepunkt im russischen Bürgerkrieg von 1917 bis 1920, partiell in den ländlichen Regionen Südrusslands und der Ukraine, wo die Fronten sehr verschwommen waren und die mobile Kriegsführung eine große Bedeutung erlangte. Später wurde sie auch von anderen Armeen übernommen, insbesondere von der [[Polnische Streitkräfte|polnischen Armee]] während des [[Polnisch-Sowjetischer Krieg|Polnisch-Sowjetischen Krieges]].

== Einsatz ==
[[Datei:Taczanka.jpg|mini|hochkant=1.5|Im Ersten Weltkrieg erbeutete russische Tatschanka in Berlin]]
Die Taktik des Tatschanka-Einsatzes war auf den Vorteil ihrer Schnelligkeit zur Überraschung des Feindes ausgerichtet. Die Tatschankas waren vor der Einführung von [[Panzer]]n oder [[Automobil]]en der einzige Weg, eine hohe Mobilität für schwere und sperrige Waffen auf dem Gefechtsfeld im [[Erster Weltkrieg|Ersten Weltkrieg]] zu erreichen. Die Geschwindigkeit der von Pferden gezogenen Wagen wurde genutzt, um die MG-Plattform in eine günstige Schussposition zu bringen, dann wurde das Feuer auf den Feind eröffnet, bevor dieser eine Chance zur Gegenwehr hatte. Da das MG in Richtung des Wagenhecks montiert war, leisteten die Tatshankas auch ein effektives Feuer zur Niederhaltung der verfolgenden gegnerischen Kavallerie nach einem Überfall und dem anschließenden Rückzug.

Nestor Machno setzte als erster Tatschankas in großer Zahl ein. Mit vielen dieser Vehikel wurden feindliche Stellungen gestürmt. War es die gegnerische Kavallerie, wurde in einem abgestimmten Manöver gewendet, so dass plötzlich alle Mündungen auf einmal in die Richtung des Gegners zeigten. Danach wurden die Feuerstöße der MGs so abgegeben, dass alle auf einen bestimmten Punkt in den feindlichen Linien gingen. Dieses Manöver erforderte eine sehr präzise Abstimmung zwischen den Besatzungen. Machno war in der Lage, dieses zu perfektionieren, so dass er das Manöver nutze, um einen Sieg im Kampf mit [[Anton Iwanowitsch Denikin|Anton Denikins]] Armee im Jahre 1919 zu erringen.

== Bewaffnung ==
Trotz einer gewissen Vereinheitlichung war die Bewaffnung der Tatschankas in den meisten Fällen improvisiert. In Russland wurde standardmäßig das [[PM 1910 (Maschinengewehr)|Maxim-MG]] verwendet.

Die polnische Kavallerie nutzte in den Zeiten des Polnisch-Sowjetischen Krieges alle Arten verfügbarer MGs und schwerer MGs, beispielsweise das MG Maxim, das [[Maschinengewehr Schwarzlose|Schwarzlose-MG M.07/12]], das [[Hotchkiss M1914|Hotchkiss-MG]] oder das [[Browning M1917|Browning-MG]]. Die letzten Modelle standardisierter Tatschankas der polnischen Armee waren mit dem Ckm wz.30 ausgerüstet, einer polnischen Modifikation des Browning-MGs M1917, das auch für [[Luftabwehr]]feuer geeignet war.

== Varianten ==
Für den Aufbau eines schweren MGs (ein Maxim mit der Lafette „Sokolow“ wog bis zu 70 kg) eignete sich die oben beschriebene Art von [[Fahrgestell]] am besten.

Die Konstruktion erlebte verschiedene Veränderungen. So wurde der [[Achsschenkel]] verstärkt, Sitze für die Bedienung montiert (falls es diese nicht gab) und auch ein Waagebalken befestigt, der zur Anspannung von vier Pferden als [[Quadriga|Fächer oder Quadriga]] diente. Bei den Anarchisten wurden auch Phaetons mit aufgeklapptem Verdeck verwendet.

In den 1930er-Jahren wurde für die [[Rote Armee]] eine typisierte Tatschanka entwickelt. Es gibt Anekdoten, wonach die Qualitätskontrolle der „Tatschanka neuen Typs“ darin bestand, dass die [[Lafette]] einen Sturz aus dem dritten Stockwerk eines Gebäudes der Moskauer Fabrik „Tschesternaja“ ohne Schaden zu überstehen hatte.

<gallery widths="150">
Tatschanka skulptur.JPG|Bronzeplastik der Tatschanka von Kachowka
Tatschanka modell 01.jpg|Bauphase eines Tatschanka-Modells (Werkstatt pio)
Tatschanka modell 06.jpg|Bauphase eines Tatschanka-Modells (Werkstatt pio)
</gallery>

== Die Tatschanka in den verschiedenen Armeen ==

=== Russland bzw. Sowjetunion ===
In den Jahren des Bürgerkrieges wurde die Tatschanka in der Roten Armee die Basis für Durchbrüche, Einkreisungen und Aufklärungseinsätze.

Als zu Beginn des [[Krieg gegen die Sowjetunion 1941–1945|Überfalls auf die Sowjetunion]] in die Bewaffnung der Roten Armee LKWs, Panzer und Kleinkampfwagen eingeführt wurden, verringerte sich die Anzahl der Tatschankas rapide. Endgültig wurden sie jedoch erst bei der Umformierung der Kavallerie als [[Truppengattung]] in der Mitte der 1950er-Jahre aus dem Bestand der Roten Armee genommen.

=== Polen ===
Anfänglich vielfach improvisiert, übernahm auch die polnische Armee im Laufe der Zeit zwei Modelle der serienmäßig hergestellten Taczankas, wie sie in Polen genannt wurden. Während der Invasion in Polen im Jahr 1939 wurden sie den Kavallerie-Schwadronen als Unterstützung zur Verfügung gestellt. So erhielt jede schwere Kavallerie-Schwadron und jede Infanterie-Kompanie Taczankas.

=== Deutsches Reich ===
Auch von der deutschen [[Wehrmacht]] wurde während des Zweiten Weltkrieges die Tatschanka eingesetzt. Verwendet wurde das [[Infanteriefahrzeug]] Modell If.5, bewaffnet mit einem Doppel-MG [[MG34 (Maschinengewehr)|MG 34]] zur Luftverteidigung.

== Tatschankas im Film ==
In zwei sowjetischen Filmen spielen Tatschankas eine größere Rolle: In [[Tschapajew (Film)|Tschapajew]] (1934, deutsche Premiere 14. März 1946) und in dem nach dem Vorbild amerikanischer [[Western]] gestalteten ''Wettlauf mit dem Tod'' (1957), der am 20. Juni 1958 in der DDR Premiere feierte.

== Tatschanka heute ==
=== Russland ===
In dem kleinen russischen Dörfchen Iwanowskoje im Stadtbezirk Tschernogolowka des Moskauer Gebietes hat eine kleine Gruppe von Enthusiatsten eine „Tatschanka neuen Typs“ aus im Wald gefundenen Überresten und anhand einer originalen Blaupause wieder zum Leben erweckt. In der kleinen Werkstatt wurden alle Holzteile neu gefertigt. Für die Metallbeschläge wurden weitestgehend Originale verwendet. Nach dem erfolgreichen Aufbau dieser Tatschanka wurde eine realistische Probefahrt in voller Bespannung durchgeführt. Nachdem diese Tatschanka sogar auf dem Roten Platz präsentiert worden ist, kann sie heute in dem ''Staatlichen Militär-technischem Museum'' ([[Russische Sprache|russisch]]: Государственный Военно-технический музей) neben den Überresten einer anderen Tatschanka besichtigt werden.

<gallery widths="150">
GVTM tatschanka 01.jpg|Überreste einer im Wald gefundenen Tatschanka
GVTM tatschanka 02.jpg|Ausschnitt aus der [[Diazotypie|Blaupause]] der Werkszeichnung der „Tatschanka neuen Typs“
GVTM tatschanka 03.jpg|[[Restaurierung|Restaurierung]] der Tatschanka in der Museumswerkstatt
GVTM tatschanka 11.jpg|Die restaurierte Tatschanka im Museum GVTM
GVTM tatschanka 12.jpg|Details der Anspannung
GVTM tatschanka 13.jpg|MG-Halterung und Munitionskästen
GVTM tatschanka 14.jpg|Details unterhalb der Tatschanka
GVTM tatschanka 15.jpg|Kasten für den Futtersack und Seriennummer „0001“
</gallery>

== Siehe auch ==
* [[Streitwagen]]
* [[Technical (Kampfwagen)]]

== Quellen ==
* ''Bürgerkrieg und militärische Interventionen in der UdSSR.'' Sowjetische Enzyklopädie, Moskau 1983, S. 579.

== Weblinks ==
{{Commonscat|Tachanka}}
* {{GSE|Тачанка}}
* [http://gvtm.ru/ Staatliches Militärtechnisches Museum (Государственный Военно-технический музей)] (russisch)
* [http://www.tatschanka.de/ Beginn einer deutschen Internetseite zur Tatschanka] (deutsch)
* [http://www.tachanka.ru/ Russische Internetseite zur Tatschanka] (russisch)
* [http://handmet-military.net/cms/?p=p_28&sName=taczanka-wz.36 Bilder der Restaurierung einer polnischen Version der Tatschanka] (polnisch)
* [http://kavaleria.org.ua/books-and-articles/31-pro-vijskovu-spravu-kavaleriju/718-ukrajina- Ukrainische Webseite zum Thema „Tatschanka“] (ukrainisch)

[[Kategorie:Kavallerie]]
[[Kategorie:Truppengattung (historisch)]]
[[Kategorie:Russisches Militärfahrzeug]]

Tatschanka

2013-08-31T00:40:56Z

Someone not using his real name: /* Siehe auch */ Infanteriefahrzeug

[[Datei:Tachanka Nova Kakhovka.jpg|miniatur|Das Monument der legendären Tatschanka in [[Kachowka]]]]
Eine '''Tatschanka''' ({{RuS|тачанка}}) ist ein mit einem schweren [[Maschinengewehr]] (MG) im Heck bewaffneter, von Pferden gezogener Kampfwagen, in der Regel einfache [[Kutsche]]n oder offene Wagen. Eine Tatschanka konnte von zwei, drei oder vier Pferden gezogen werden (siehe Bild des Malers Grekow „Die MGs rücken vor“, 1925). Die Besatzung bestand aus zwei oder drei Soldaten, der MG-Bedienung und einem Kutscher (er galt auch als Ersatzmann der Bedienung). Die Tatschanka wurde angeblich von [[Nestor Machno]] erfunden.

== Namensgebung ==
Eine andere Version besagt, dass es ein verkürztes Wort von „Tawritschanka“ ist, welches holprige Transporte in der [[Ukraine|Südukraine]] und auf der [[Krim]] bezeichnet, abgeleitet von dem regionalen Ausdruck „Taurida“. Später veränderte sich das Wort zu „Tatschanka“. Jedoch bezeichnet „Tawritschanka“ ein großes Fuhrwerk, ähnlich einem [[Leiterwagen]] mit einem hölzernen Wagenkasten, die Tatschanka dagegen hatte eine leichte Besatzung, keinen Aufbau und war gefedert. Das Vorhandensein einer Federung war grundlegend für die Geschwindigkeit bei Fahrten auf Feldwegen bzw. weglosen Flächen sowie für die Treffgenauigkeit beim Schießen.

Die Anhänger Nestor Machnos wiesen im Zusammenhang mit der Bezeichnung auf das ukrainische Wort ''netytschanka'' („нетичанка“), was einen leichten, gefederten Wagen bedeutete. Ihrer Meinung nach kam die Bezeichnung daher, dass die Achsen des Fahrgestells den Aufbau nicht berührten („нэ тыкалысь“ auf Ukrainisch).

Oleg N. Trubatschow und auch derzeitige Experten leiten die Bezeichnung ebenfalls aus dem ukrainischen „netytschanka“ ab, das vom polnischen Wort ''najtyczanka'' – einer Art von Vehikel / [[Kalesche]] – herrührt. Das polnische Wort wiederum stammt von dem deutschen Namen des Gebietes [[Neu-Titschein]] in [[Tschechien]] ab.

== Geschichte ==
Im [[Russischer Bürgerkrieg|Bürgerkrieg]] wurde die Tatschanka einerseits zur Truppenverlegung und zur Führung unerwarteter Schläge auf dem Gefechtsfeld verwendet. Besondere Popularität erhielt die Tatschanka bei den Anhängern Nestor Machnos. Letztere verwandten die Tatschanka nicht nur im Kampf, sondern auch zur Verlegung der [[Infanterie]]. Dabei entsprach die Marschgeschwindigkeit der [[Kavallerie]]truppen im Trab. Damit erreichten die Abteilungen Machnos leicht bis zu 100 km pro Tag und das über mehrere Tage in Folge. So schafften große Kräfte von Machno nach dem entscheidenden Durchbruch bei Peregonowka die Strecke von 600 km zwischen Umana bis Guljai-Polja in elf Tagen und nahmen überraschend Nachschubgarnisonen der [[Weiße Armee|Weißen]] ein.

Die Verwendung der Tatschanka erreichte ihren Höhepunkt im russischen Bürgerkrieg von 1917 bis 1920, partiell in den ländlichen Regionen Südrusslands und der Ukraine, wo die Fronten sehr verschwommen waren und die mobile Kriegsführung eine große Bedeutung erlangte. Später wurde sie auch von anderen Armeen übernommen, insbesondere von der [[Polnische Streitkräfte|polnischen Armee]] während des [[Polnisch-Sowjetischer Krieg|Polnisch-Sowjetischen Krieges]].

== Einsatz ==
[[Datei:Taczanka.jpg|mini|hochkant=1.5|Im Ersten Weltkrieg erbeutete russische Tatschanka in Berlin]]
Die Taktik des Tatschanka-Einsatzes war auf den Vorteil ihrer Schnelligkeit zur Überraschung des Feindes ausgerichtet. Die Tatschankas waren vor der Einführung von [[Panzer]]n oder [[Automobil]]en der einzige Weg, eine hohe Mobilität für schwere und sperrige Waffen auf dem Gefechtsfeld im [[Erster Weltkrieg|Ersten Weltkrieg]] zu erreichen. Die Geschwindigkeit der von Pferden gezogenen Wagen wurde genutzt, um die MG-Plattform in eine günstige Schussposition zu bringen, dann wurde das Feuer auf den Feind eröffnet, bevor dieser eine Chance zur Gegenwehr hatte. Da das MG in Richtung des Wagenhecks montiert war, leisteten die Tatshankas auch ein effektives Feuer zur Niederhaltung der verfolgenden gegnerischen Kavallerie nach einem Überfall und dem anschließenden Rückzug.

Nestor Machno setzte als erster Tatschankas in großer Zahl ein. Mit vielen dieser Vehikel wurden feindliche Stellungen gestürmt. War es die gegnerische Kavallerie, wurde in einem abgestimmten Manöver gewendet, so dass plötzlich alle Mündungen auf einmal in die Richtung des Gegners zeigten. Danach wurden die Feuerstöße der MGs so abgegeben, dass alle auf einen bestimmten Punkt in den feindlichen Linien gingen. Dieses Manöver erforderte eine sehr präzise Abstimmung zwischen den Besatzungen. Machno war in der Lage, dieses zu perfektionieren, so dass er das Manöver nutze, um einen Sieg im Kampf mit [[Anton Iwanowitsch Denikin|Anton Denikins]] Armee im Jahre 1919 zu erringen.

== Bewaffnung ==
Trotz einer gewissen Vereinheitlichung war die Bewaffnung der Tatschankas in den meisten Fällen improvisiert. In Russland wurde standardmäßig das [[PM 1910 (Maschinengewehr)|Maxim-MG]] verwendet.

Die polnische Kavallerie nutzte in den Zeiten des Polnisch-Sowjetischen Krieges alle Arten verfügbarer MGs und schwerer MGs, beispielsweise das MG Maxim, das [[Maschinengewehr Schwarzlose|Schwarzlose-MG M.07/12]], das [[Hotchkiss M1914|Hotchkiss-MG]] oder das [[Browning M1917|Browning-MG]]. Die letzten Modelle standardisierter Tatschankas der polnischen Armee waren mit dem Ckm wz.30 ausgerüstet, einer polnischen Modifikation des Browning-MGs M1917, das auch für [[Luftabwehr]]feuer geeignet war.

== Varianten ==
Für den Aufbau eines schweren MGs (ein Maxim mit der Lafette „Sokolow“ wog bis zu 70 kg) eignete sich die oben beschriebene Art von [[Fahrgestell]] am besten.

Die Konstruktion erlebte verschiedene Veränderungen. So wurde der [[Achsschenkel]] verstärkt, Sitze für die Bedienung montiert (falls es diese nicht gab) und auch ein Waagebalken befestigt, der zur Anspannung von vier Pferden als [[Quadriga|Fächer oder Quadriga]] diente. Bei den Anarchisten wurden auch Phaetons mit aufgeklapptem Verdeck verwendet.

In den 1930er-Jahren wurde für die [[Rote Armee]] eine typisierte Tatschanka entwickelt. Es gibt Anekdoten, wonach die Qualitätskontrolle der „Tatschanka neuen Typs“ darin bestand, dass die [[Lafette]] einen Sturz aus dem dritten Stockwerk eines Gebäudes der Moskauer Fabrik „Tschesternaja“ ohne Schaden zu überstehen hatte.

<gallery widths="150">
Tatschanka skulptur.JPG|Bronzeplastik der Tatschanka von Kachowka
Tatschanka modell 01.jpg|Bauphase eines Tatschanka-Modells (Werkstatt pio)
Tatschanka modell 06.jpg|Bauphase eines Tatschanka-Modells (Werkstatt pio)
</gallery>

== Die Tatschanka in den verschiedenen Armeen ==

=== Russland bzw. Sowjetunion ===
In den Jahren des Bürgerkrieges wurde die Tatschanka in der Roten Armee die Basis für Durchbrüche, Einkreisungen und Aufklärungseinsätze.

Als zu Beginn des [[Krieg gegen die Sowjetunion 1941–1945|Überfalls auf die Sowjetunion]] in die Bewaffnung der Roten Armee LKWs, Panzer und Kleinkampfwagen eingeführt wurden, verringerte sich die Anzahl der Tatschankas rapide. Endgültig wurden sie jedoch erst bei der Umformierung der Kavallerie als [[Truppengattung]] in der Mitte der 1950er-Jahre aus dem Bestand der Roten Armee genommen.

=== Polen ===
Anfänglich vielfach improvisiert, übernahm auch die polnische Armee im Laufe der Zeit zwei Modelle der serienmäßig hergestellten Taczankas, wie sie in Polen genannt wurden. Während der Invasion in Polen im Jahr 1939 wurden sie den Kavallerie-Schwadronen als Unterstützung zur Verfügung gestellt. So erhielt jede schwere Kavallerie-Schwadron und jede Infanterie-Kompanie Taczankas.

=== Deutsches Reich ===
Auch von der deutschen [[Wehrmacht]] wurde während des Zweiten Weltkrieges die Tatschanka eingesetzt. Verwendet wurde das Modell Jf.5, bewaffnet mit einem Doppel-MG [[MG34 (Maschinengewehr)|MG 34]] zur Luftverteidigung.

== Tatschankas im Film ==
In zwei sowjetischen Filmen spielen Tatschankas eine größere Rolle: In [[Tschapajew (Film)|Tschapajew]] (1934, deutsche Premiere 14. März 1946) und in dem nach dem Vorbild amerikanischer [[Western]] gestalteten ''Wettlauf mit dem Tod'' (1957), der am 20. Juni 1958 in der DDR Premiere feierte.

== Tatschanka heute ==
=== Russland ===
In dem kleinen russischen Dörfchen Iwanowskoje im Stadtbezirk Tschernogolowka des Moskauer Gebietes hat eine kleine Gruppe von Enthusiatsten eine „Tatschanka neuen Typs“ aus im Wald gefundenen Überresten und anhand einer originalen Blaupause wieder zum Leben erweckt. In der kleinen Werkstatt wurden alle Holzteile neu gefertigt. Für die Metallbeschläge wurden weitestgehend Originale verwendet. Nach dem erfolgreichen Aufbau dieser Tatschanka wurde eine realistische Probefahrt in voller Bespannung durchgeführt. Nachdem diese Tatschanka sogar auf dem Roten Platz präsentiert worden ist, kann sie heute in dem ''Staatlichen Militär-technischem Museum'' ([[Russische Sprache|russisch]]: Государственный Военно-технический музей) neben den Überresten einer anderen Tatschanka besichtigt werden.

<gallery widths="150">
GVTM tatschanka 01.jpg|Überreste einer im Wald gefundenen Tatschanka
GVTM tatschanka 02.jpg|Ausschnitt aus der [[Diazotypie|Blaupause]] der Werkszeichnung der „Tatschanka neuen Typs“
GVTM tatschanka 03.jpg|[[Restaurierung|Restaurierung]] der Tatschanka in der Museumswerkstatt
GVTM tatschanka 11.jpg|Die restaurierte Tatschanka im Museum GVTM
GVTM tatschanka 12.jpg|Details der Anspannung
GVTM tatschanka 13.jpg|MG-Halterung und Munitionskästen
GVTM tatschanka 14.jpg|Details unterhalb der Tatschanka
GVTM tatschanka 15.jpg|Kasten für den Futtersack und Seriennummer „0001“
</gallery>

== Siehe auch ==
* [[Infanteriefahrzeug]]
* [[Streitwagen]]
* [[Technical (Kampfwagen)]]

== Quellen ==
* ''Bürgerkrieg und militärische Interventionen in der UdSSR.'' Sowjetische Enzyklopädie, Moskau 1983, S. 579.

== Weblinks ==
{{Commonscat|Tachanka}}
* {{GSE|Тачанка}}
* [http://gvtm.ru/ Staatliches Militärtechnisches Museum (Государственный Военно-технический музей)] (russisch)
* [http://www.tatschanka.de/ Beginn einer deutschen Internetseite zur Tatschanka] (deutsch)
* [http://www.tachanka.ru/ Russische Internetseite zur Tatschanka] (russisch)
* [http://handmet-military.net/cms/?p=p_28&sName=taczanka-wz.36 Bilder der Restaurierung einer polnischen Version der Tatschanka] (polnisch)
* [http://kavaleria.org.ua/books-and-articles/31-pro-vijskovu-spravu-kavaleriju/718-ukrajina- Ukrainische Webseite zum Thema „Tatschanka“] (ukrainisch)

[[Kategorie:Kavallerie]]
[[Kategorie:Truppengattung (historisch)]]
[[Kategorie:Russisches Militärfahrzeug]]

Todesstrafe in Belarus

2013-08-07T12:43:14Z

Someone not using his real name: /* Public opinion */

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]] ([[:ru:Алкаев, Олег Леонидович|Олег Алкаев]]), on the day of execution the convict is transported to a secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots the convict in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. About 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

== External links ==
* [http://www.dailymotion.com/video/x8ru9w_oleg-alkaev-former-head-of-belarus_news Interview with Oleg Alkaev, former head of Belarus's death row]

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T23:33:58Z

Someone not using his real name: /* Method */

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]] ([[:ru:Алкаев, Олег Леонидович|Олег Алкаев]]), on the day of execution the convict is transported to a secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots the convict in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

== External links ==
* [http://www.dailymotion.com/video/x8ru9w_oleg-alkaev-former-head-of-belarus_news Interview with Oleg Alkaev, former head of Belarus's death row]

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T21:28:00Z

Someone not using his real name: /* Method */

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]], on the day of execution the convict is transported to a secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots the convict in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

== External links ==
* [http://www.dailymotion.com/video/x8ru9w_oleg-alkaev-former-head-of-belarus_news Interview with Oleg Alkaev, former head of Belarus's death row]

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T21:18:13Z

Someone not using his real name: /* References */ his account is slightly different in this interview than in the book as recounted by CBS

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]], on the day of execution the convict is transported to a secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots him in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

== External links ==
* [http://www.dailymotion.com/video/x8ru9w_oleg-alkaev-former-head-of-belarus_news Interview with Oleg Alkaev, former head of Belarus's death row]

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T21:13:53Z

Someone not using his real name: /* Method */

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]], on the day of execution the convict is transported to a secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots him in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T21:12:41Z

Someone not using his real name: /* Method */ probably that one

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]], on the day of execution the convict is transported to secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots him in the back of his head with a [[PB (pistol)|PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Todesstrafe in Belarus

2013-08-06T21:11:29Z

Someone not using his real name: /* Method */ Transferred info from the article on Russia, where it had been added incorrectly (by WP:SYNT

{{capital punishment}}
The provision for '''Capital punishment in Belarus''' has been a part of the country since gaining independence from the [[Soviet Union]]. The current [[Constitution of Belarus|national constitution]] prescribes this punishment for "grave crimes." Later laws have clarified the specific crimes for which capital punishment can be used. Capital punishment can be issued for crimes that occur against the state or against individuals. A few non-violent crimes can be issued with the sentence of capital punishment. According to [[Amnesty International]], [[Belarus]] is the last country in the [[Commonwealth of Independent states|CIS]] and the whole of Europe to execute criminals.<ref>Amnesty International- Document- Commonwealth of Independent states: Belarus- the last executioner</ref>

Following a referendum on the issue, the Belarusian government has taken steps to change the way capital punishment is sentenced and carried out.<ref name="byemb">Embassy of Belarus in the United Kingdom [http://www.belembassy.org/uk/capital.html Capital Punishment in Belarus and Changes of Belarus Criminal Legislation related thereto]. Retrieved May 29, 2007.</ref> International organisations, such as the United Nations, have criticised the methods Belarus uses when carrying out capital punishment. The use of capital punishment is one factor keeping the country out of the [[Council of Europe]].<ref name="brestonline">{{Cite web|url=http://brestonline.com/en/news/archy2001m4.html|title=Seminar on death penalty abolition held in Brest|accessdate=2007-11-03|publisher=BrestOnline|date=2001-04-05|author=Belpan}}</ref>

==Legislation==
Article 24 of the [[Constitution of Belarus]] states that:
{{cquote|Until its abolition, the death sentence may be applied in accordance with the law as an exceptional penalty for especially grave crimes and only in accordance with the [[verdict]] of a court of law."<ref name="bycon">[http://law.by/work/EnglPortal.nsf/6e1a652fbefce34ac2256d910056d559/d93bc51590cf7f49c2256dc0004601db?OpenDocument Constitution of the Republic of Belarus]. Accessed on 5 September 2005.</ref>}}

As per the [[Criminal Code of Belarus|Criminal Code of the Republic of Belarus]], capital punishment can be imposed for the following acts:

*Launching or conducting [[War of aggression|aggressive war]] (Article 122, Part 2)
*Murder of a representative of a foreign state or international organization in order to provoke international complications or war (Article 124, Part 2)
*International [[terrorism]] (Article 126)
*[[Genocide]] (Article 127)
*[[Crime against humanity]] (Article 128)
*Application of [[weapons of mass destruction]] under international treaties of the Republic of Belarus (Article 134)
*Violation of the [[Laws of war|war laws and usage]] (Article 135, Part 3)
*[[Murder]] committed under aggravating circumstances (Article 139, Part 2)
*[[Terrorism]] (Article 289, Part 3)
*[[Treason]] connected with murder (Article 356, Part 2)
*[[Revolution|Conspiracy to seize state power]] (Article 357, Part 3)
*Terrorist acts (Article 359)
*[[Sabotage]] (Article 360, Part 2)
*Murder of a [[police officer]]. (Article 362) <ref name="belarusembassy.org">Embassy of the Republic of Belarus in the United States. [http://www.belarusembassy.org/humanitarian/criminalcode.htm On the Use of Death Penalty in the Republic of Belarus]. Published 2004. Retrieved May 29, 2007.</ref>
Most of the death penalty convictions were for murder committed under aggravating circumstances.<ref name="mvd02">{{Cite web|url=http://mvd.gov.by/modules.php?name=News&file=article&sid=1375|title=Смертная казнь|accessdate=2007-11-03|publisher=BrestOnline|date=2002-11-06|author=газете «Труд-7» |language=Russian}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> Court proceedings involving capital cases must involve a "collegial consideration," consisting of one judge and two People's assessors. The People's assessors are chosen from the general population, similar to the [[jury]] system.<ref>{{cite web|url=http://ncpi.gov.by/constsud/eng/d114.htm |title=DECISION OF THE CONSTITUTIONAL COURT OF THE REPUBLIC OF BELARUS OF 17.04.2001 No. D-114/2001 |accessdate=2008-03-11 |date=2001-04-17 |publisher=Constitutional Court of the Republic of Belarus |archiveurl = http://web.archive.org/web/20071006165746/http://ncpi.gov.by/constsud/eng/d114.htm  |archivedate = 2007-10-06}}</ref>

Over the years, the number of offenses inviting death penalty and the type of convicts eligible for the same have reduced. In 1993, four [[economic crime]]s which would have resulted in death penalty during the [[Soviet Union|Soviet]] era were removed from the list of capital offenses by a vote of parliament and were replaced by prison terms without parole.<ref name="aibyuz">"[http://web.amnesty.org/library/Index/ENGEUR040092004?open&of=ENG-BLR Belarus and Uzbekistan: the last executioners]." [[Amnesty International]]. Accessed on 5 September 2005.</ref> Although the total number of categories of crime qualifying for capital punishment declined during this time, Presidential Decree No. 21, issued on 21 October 1997, added "terrorism" to the list of capital offenses.<ref name="ai491797">{{Cite web|url=http://web.amnesty.org/library/Index/ENGEUR490171997?open&of=ENG-2EU|title=Belarus: Findings of Human Rights Committee confirm worsening human rights situation|accessdate=2007-11-03|date=1997-11-10|author=Amnesty International}} {{Dead link|date=November 2010|bot=H3llBot}}</ref> When the Criminal Code was updated in 1999, the number of capital offenses was further reduced. This reduction was assisted by the introduction of [[life imprisonment]] in December 1997.<ref name="byemb"/>

Since March 1, 1994, women are ineligible for capital punishment and those under the age of 18 at the time of the crime or over 65 at the time of sentencing were exempt from capital punishment since January 2001.<ref name="bycode">{{Cite web|url=http://www.levonevski.net/pravo/kodeksy/uk/009.html|title=Уголовный кодекс Республики Беларусь|accessdate=2007-11-03|date=2006-04-02|language=Russian}}</ref> Those who are [[mentally ill]] may have their death sentence commuted.<ref name="belarusembassy.org"/> Under Article 84 of the Constitution, the [[President of Belarus|president]] "may grant [[pardon]]s to convicted citizens".<ref name="bycon"/> From June 30, 2003 to June 30, 2005, President [[Alexander Lukashenko]] granted two pardons to death row inmates and denied one such request.<ref name="byemb"/>

In 2000, the [[Parliamentary Assembly of the Council of Europe|Parliamentary Assembly]] of the [[Council of Europe]] condemned:

''"in the strongest possible terms the executions in Belarus and deplores the fact that Belarus is currently the only country in Europe where the death penalty is enforced and, moreover, is regularly and widely enforced".<ref>Legisltationline.org [http://www.legislationline.org/?jid=7&less=false&tid=144 Death Penalty - Belarus]. Published November 2004. Retrieved May 29, 2007.</ref>''

Belarus is now also the only European nation that issues the sentence during times of peace as well as war. The European Council members suggested in 2001 that Belarus abolish capital punishment before it can apply for membership in the Council.<ref name="brestonline"/> Belarus (as the [[Byelorussian SSR]]) signed the [[International Covenant on Civil and Political Rights]] in 1973.<ref>United Nations Office of the High Commissioner for Human Rights. [http://www.ohchr.org/english/countries/ratification/4.htm Signatory nations of the ICCPR]. Retrieved May 29, 2007.</ref> This convention, however, does not abolish the death penalty, but it imposes certain conditions on its implementation and use.

==Method==
Before execution, all prisoners on [[death row]] are transferred to Minsk Detention Center No. 1 (СИЗО, or [[SIZO No. 1]]), located in the capital city of [[Minsk]].<ref name="unchhr"/> The method used to carry out the sentence is [[execution by shooting]].<ref name="mvd02"/> The executioner is a member of the "Committee for the execution of sentences," which also chooses the area where the execution will take place.<ref name="unchhr">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/0/2b1c441baa682a5fc1256d250036448c?Opendocument|title=Communication No 887/1999 : Belarus. 24/04/2003|accessdate=2007-11-03|publisher=United Nations Organization|date=2003-04-24|author=Human Rights Committee}}</ref> According to the book ''The Death Squad'' by [[Oleg Alkayev]], on the day of execution the convict is transported to secret location where he is told by officials that all appeals have been rejected. Without being allowed to see a priest, the convict is then blindfolded and taken to a nearby room, where two staffers force him to kneel in front of a bullet backstop. The executioner then shoots him in the back of his head with a [[PB-9 pistol]] equipped with a silencer. According to Alkayev, "The whole procedure, starting with the announcement about denied appeals and ending with the gunshot, lasts no longer than two minutes".<ref>[http://www.cbsnews.com/stories/2009/10/13/ap/world/main5381578.shtml Gypsy Laborer Faces Execution In Belarus] CBS News, October 13, 2009</ref>

After the sentence is carried out, a prison doctor and other prison officials certify that the execution has been carried out, and a [[death certificate]] is prepared. The remains of the condemned are buried secretly, and the family is notified that the execution took place.<ref name="mvd02"/> Col. Oleg Alkayev, who was a director of SIZO No. 1, claimed that about 130 executions took place at the prison between December 1996 and May 2001, when he left Belarus to live in exile in [[Berlin]], [[Germany]].<ref name="alkayev">{{Cite web|url=http://www.santegidio.org/pdm/news/29_08_01.htm|title=Belarus Executioner Accuses President of Murder|accessdate=2007-11-03|publisher=Reuters|date=2001-08-29}}</ref>

The [[United Nations]] [[Human Rights Committee]] issued the following opinion of the execution process in Belarus after the mother of subsequently executed prisoner Anton Bondarenko petitioned the Committee to spare her son's life:

{{cquote|[the process has] the effect of intimidating or punishing families by intentionally leaving them in a state of uncertainty and mental distress…[and that the] authorities’ initial failure to notify the author of the scheduled date for the execution of her son, and their subsequent persistent failure to notify her of the location of her son’s grave amounts to inhuman treatment of the author, in violation of article 7 of the Covenant [prohibiting torture or cruel, inhuman or degrading treatment or punishment].<ref name="schedko">{{Cite web|url=http://www.unhchr.ch/tbs/doc.nsf/(Symbol)/399cc6c62d92bbcec1256d33004d5600?Opendocument|title=Communication No 886/1999 : Belarus. 28/04/2003|accessdate=2007-11-17|publisher=United Nations|year=2003|author=Human Rights Committee}}</ref>}}

== Number of executions ==
The following is a rough estimate of number of executions carried out since 1990, as per Belarusian Ministry of Internal Affairs (MVD):
*1990 – 20
*1991 – 14
*1993 – 20
*1994 – 24
*1995 – 46
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7 <ref name="mvd02"/>
*2007 – at least one
*2008 – at least 4
*2009 – 0
*2010 – 2
*2011 – 2 <ref>[http://www.amnestyusa.org/news/news-item/execution-of-belarus-death-row-prisoner-confirmed Execution of Belarus death row prisoner confirmed] Amnesty International on July 26, 2011, accessed on August 31, 2011.</ref>
*2012 – 0

The exact number of people executed in Belarus is not known, since the last documents released by the Belarusian Government were in 2006.<ref name="ihf06">{{Cite web|url=http://www.osce.org/documents/odihr/2006/10/21160_en.pdf|title=IHF Intervention to the 2006 OSCE Human Dimension Implementation Meeting|accessdate=2007-11-17|year=2006|author=International Helsinki Federation for Human Rights|format=PDF}}</ref> Moreover other sources, notably BelaPAN, have published somewhat different data. BelaPAN, the abbreviation for "Беларускае прыватнае агентства навiн" (Belarusian Private News Agency), records 278 executions from 1992 to 2010 with two additional men under death sentence in September 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref> Due to some of the practices of the MVD, such as the non-disclosure of the graves of the executed, this is a violation of the [[Organization for Security and Cooperation in Europe]] protocol to make information about capital punishment open to the public.<ref name="oscedp">{{Cite web|url=http://www.osce.org/documents/odihr/2004/02/2159_en.pdf|title=OSCE Comments on the Death Penalty|accessdate=2007-11-17|publisher=Organization for Security and Cooperation in Europe|year=1994|format=PDF}}</ref>

Executions in Belarus between 1985 and 2010 (BelaPAN 2010):

*1985 – 21 – Belarus SSR
*1986 – 10
*1987 – 12
*1988 – 12
*1989 – 5
*1990 – 20
*1991 – 21
*1992 – 24 – Independent
*1993 – 20
*1994 – 25
*1995 – 27
*1996 – 29
*1997 – 46
*1998 – 47
*1999 – 13
*2000 – 4
*2001 – 7
*2002 – 4
*2003 – 4
*2004 – 5
*2005 – 5
*2006 – 9
*2007 – 3
*2008 – 2
*2009 – 2
*2010 – 2

==Public opinion==
In a [[Belarusian referendum, 1996|1996 referendum]], one of the seven questions asked was about the opinion of Belarusian people about abolishing the death penalty. According to the results of this referendum, 80.44% of Belorussians were against abolishing the death penalty.<ref name="96refresult">{{Cite web|url=http://www.rec.gov.by/refer/ref1996resdoc.html|title=Центральной комиссии Республики Беларусь по выборам и проведению республиканских референдумов|accessdate=2007-11-17|year=1996|language=Russian}}</ref> However, at the time of the referendum, the longest available prison sentence was 15 years. Since then, the sentence of lifelong imprisonment was introduced, in December 1997. There have not been more recent surveys to determine whether the change in maximum prison sentence affected public sentiment about the death penalty.<ref name="aibyuz"/>

More recently a parliamentary special working group announced plans to conduct a public opinion poll, but the Information and Analytical Center with the Administration of the President took over this undertaking. The Center has released its report, “Public Opinion about the Activity of the Organs of Internal Affairs of the Republic of Belarus,” which included the questions about death penalty and the attitudes of Belarusian citizens about abolition of capital punishment. That poll showed only 4.5% of the respondents were against capital punishment in all cases. 79.5% considered capital punishment appropriate punishment for at least some grave crimes. But about 10% had a difficulty answering these questions or offered no opinion.<ref>Prudnikova, Olga (2010) “The Question Connected with Death Punishment Will Be Solved After the Elections?” Svobodnye Novosti Plus, 11.08.2010-18.08.2010, p. 12: (www.naviny.by)</ref>

There have been several steps toward reducing the use of the death penalty in Belarus. The Law of the Republic of Belarus of 31 December 1997 added Article 22 which allows for “imprisonment for the term of one’s life (life imprisonment) as an alternative to capital punishment.” Three categories of persons no longer may be executed: people under 18 years of age, women, and men over 65 years.<ref>Kadushkin, S. (2002) “Death Penalty and Its Alternative in the Legislation of the Republic of Belarus,” Yustitsiya of Belarus, 3</ref>

== Court cases ==
On March 11, 2004, the [[Constitutional Court of the Republic of Belarus]] came to the conclusion that two articles of the Criminal Code were incompatible with the [[Constitution of Belarus]]. The Court stated that either the President or the National Assembly could make the decision to suspend or completely abolish the death penalty.<ref>[http://ncpi.gov.by/ConstSud/eng/j171.htm Judgment of the Constitutional Court of March 11, 2004] On the conformity between the Constitution of the Republic of Belarus, the international treaties to which the Republic of Belarus is a party and the provisions of the Criminal Code of the Republic of Belarus stipulating application of the death penalty as a punishment, accessed on May 28, 2006.</ref> Subsequently, in October 2005, the Parliament adopted an amendment to the Criminal Code declaring that the continued use of the death penalty was on a temporary basis only.<ref>[http://www.charter97.org/eng/news/2005/10/27/uk Belarus amends criminal code] Interfax on October 26, 2005, accessed on May 28, 2006.</ref> There were three executions on February, 2008.,<ref>[http://ipsnews.net/news.asp?idnews=42789 Three get executed] & [http://www.data.minsk.by/belarusnews/062008/80.html E.C. is upset]</ref> but only two recorded by BelaPAN, with two more in 2009 according to BelaPAN and two in March 2010.<ref>Kania, Richard R. E., and Lyuba Pervushina, “The Death Penalty in Belarus,” paper for the Southern Criminal Justice Association 2010 Annual Meeting, Clearwater Beach, Florida</ref>

==References==
{{Portal|Belarus|Criminal justice}}
{{Reflist|2}}

{{Capital punishment in Europe}}

[[Category:Capital punishment by country|Belarus]]
[[Category:Belarusian law]]
[[Category:Death in Belarus]]

Brandrodung in Südostasien

2013-08-02T17:50:01Z

Someone not using his real name:

{{multiple issues|
{{POV|date=July 2013}}
{{original research|date=July 2013}}
{{ref improve|date=July 2013}}
}}
{{quotebox|'''"They only have to be sparked by cigarette butts and they (peatlands) will go up in flames"|Achmad Taufik, South Sumatra Forestry Office'''<ref>{{Cite web|url=http://www.thejakartapost.com/news/2012/08/15/slash-and-burn-practices-lead-forest-fires-s-sumatra.html|title=Slash-and-burn practices lead to forest fires in S. Sumatra|first=Ansyor|last=Idrus|work=The Jakarta Post|date=15 August 2012}}</ref>}}
The '''Southeast Asian haze''' is a perennial [[air quality]] problem stemming from [[slash and burn]] deforestation techniques coupled with expansion of the [[palm oil]] industry, mainly originating in the [[Indonesian]] island of [[Sumatra]], but its effects are felt in [[Singapore]] and [[Malaysia]] as well.<Ref name="time2013"/>

Traditionally, the large [[multinational corporation]]s had been blamed, but in recent years the small- to medium-size plantations have been found to start the majority of fires.<Ref name="time2013">http://world.time.com/2013/07/30/the-southeast-asian-haze-is-back-and-worse-may-follow/</ref>

The problem flares up every dry season, in varying degrees, and affects Malaysia, Singapore, Brunei, southern Thailand, and Indonesia. Rice paddy burning is also a common practice throughout Southeast Asia, resulting in poor air quality at a local level.

==Haze by year==
It generally refers to [[haze]] occurring in Southeast Asia; see [[Smog#Southeast Asia]]. In specific intense cases, it may refer to:
*[[1997 Southeast Asian haze]]
*[[1997 Indonesian forest fires]]
*[[2005 Malaysian haze]]
*[[2006 Southeast Asian haze]]
*[[2009 Southeast Asian haze]]
*[[2013 Southeast Asian haze]]

==See also==
*[[ASEAN Agreement on Transboundary Haze Pollution]]

==References==
{{Reflist|30em}}

{{Asia Pollution}}
{{Palm oil}}

[[Category:Southeast Asian haze| ]]

{{environmental-disaster-stub}}
{{Indonesia-stub}}

Brandrodung in Südostasien

2013-08-02T17:47:55Z

Someone not using his real name: This is contradicted, at least with respect to recent years, by Time article. Removed some non-informational verbiage

{{multiple issues|
{{POV|date=July 2013}}
{{original research|date=July 2013}}
{{ref improve|date=July 2013}}
}}
{{quotebox|'''"They only have to be sparked by cigarette butts and they (peatlands) will go up in flames"|Achmad Taufik, South Sumatra Forestry Office'''<ref>{{Cite web|url=http://www.thejakartapost.com/news/2012/08/15/slash-and-burn-practices-lead-forest-fires-s-sumatra.html|title=Slash-and-burn practices lead to forest fires in S. Sumatra|first=Ansyor|last=Idrus|work=The Jakarta Post|date=15 August 2012}}</ref>}}
The '''Southeast Asian haze''' is a perennial [[air quality]] problem stemming from [[slash and burn]] deforestation techniques coupled with expansion of the [[palm oil]] industry, mainly originating in the [[Indonesian]] island of [[Sumatra]], but its effects are felt in [[Singapore]] and [[Malaysia]] as well.<Ref name="time2013"/>

Traditionally, the large [[multinational]] corporations had been blamed, but in recent years the small to medium-size plantations have been found to start the majority of fires.<Ref name="time2013">http://world.time.com/2013/07/30/the-southeast-asian-haze-is-back-and-worse-may-follow/</ref>

The problem flares up every dry season, in varying degrees, and affects Malaysia, Singapore, Brunei, southern Thailand, and Indonesia. Rice paddy burning is also a common practice throughout Southeast Asia, resulting in poor air quality at a local level.

==Haze by year==
It generally refers to [[haze]] occurring in Southeast Asia; see [[Smog#Southeast Asia]]. In specific intense cases, it may refer to:
*[[1997 Southeast Asian haze]]
*[[1997 Indonesian forest fires]]
*[[2005 Malaysian haze]]
*[[2006 Southeast Asian haze]]
*[[2009 Southeast Asian haze]]
*[[2013 Southeast Asian haze]]

==See also==
*[[ASEAN Agreement on Transboundary Haze Pollution]]

==References==
{{Reflist|30em}}

{{Asia Pollution}}
{{Palm oil}}

[[Category:Southeast Asian haze| ]]

{{environmental-disaster-stub}}
{{Indonesia-stub}}

Brandrodung in Südostasien

2013-08-02T17:35:22Z

Someone not using his real name:

{{Article for deletion/dated|page=Southeast Asian haze|timestamp=20130728151131|year=2013|month=July|day=28|substed=yes|help=off}}


{{multiple issues|
{{POV|date=July 2013}}
{{original research|date=July 2013}}
{{ref improve|date=July 2013}}
}}
{{quotebox|'''"They only have to be sparked by cigarette butts and they (peatlands) will go up in flames"|Achmad Taufik, South Sumatra Forestry Office'''<ref>{{Cite web|url=http://www.thejakartapost.com/news/2012/08/15/slash-and-burn-practices-lead-forest-fires-s-sumatra.html|title=Slash-and-burn practices lead to forest fires in S. Sumatra|first=Ansyor|last=Idrus|work=The Jakarta Post|date=15 August 2012}}</ref>}}
'''Southeast Asian haze''' is huge perennial air quality and health problem stemming from [[slash and burn]] deforestation techniques coupled with expansion of the [[palm oil]] industry<Ref>http://world.time.com/2013/07/30/the-southeast-asian-haze-is-back-and-worse-may-follow/</ref> at the expense of new and old growth forest, driven by desires for hard currency, employment, and large profits; largely controlled by multinational corporations. This mainly occurs in the [[Indonesian]] island of [[Sumatra]] The largest of the multinational corporations responsible for the deforestation are [[Wilmar International]] and [[Cargill]].

The problem flares up every dry season, in varying degrees, and affects Malaysia, Singapore, Brunei, southern Thailand, and Indonesia. Rice paddy burning is also a common practice throughout Southeast Asia, resulting in poor air quality at a local level.

==Haze by year==
It generally refers to [[haze]] occurring in Southeast Asia; see [[Smog#Southeast Asia]]. In specific intense cases, it may refer to:
*[[1997 Southeast Asian haze]]
*[[1997 Indonesian forest fires]]
*[[2005 Malaysian haze]]
*[[2006 Southeast Asian haze]]
*[[2009 Southeast Asian haze]]
*[[2013 Southeast Asian haze]]

==See also==
*[[ASEAN Agreement on Transboundary Haze Pollution]]

==References==
{{Reflist|30em}}

{{Asia Pollution}}
{{Palm oil}}

[[Category:Southeast Asian haze| ]]

{{environmental-disaster-stub}}
{{Indonesia-stub}}

Brandrodung in Südostasien

2013-08-02T17:35:05Z

Someone not using his real name: covers the other reason too

{{Article for deletion/dated|page=Southeast Asian haze|timestamp=20130728151131|year=2013|month=July|day=28|substed=yes|help=off}}


{{multiple issues|
{{POV|date=July 2013}}
{{original research|date=July 2013}}
{{ref improve|date=July 2013}}
}}
{{quotebox|'''"They only have to be sparked by cigarette butts and they (peatlands) will go up in flames"|Achmad Taufik, South Sumatra Forestry Office'''<ref>{{Cite web|url=http://www.thejakartapost.com/news/2012/08/15/slash-and-burn-practices-lead-forest-fires-s-sumatra.html|title=Slash-and-burn practices lead to forest fires in S. Sumatra|first=Ansyor|last=Idrus|work=The Jakarta Post|date=15 August 2012}}</ref>}}
'''Southeast Asian haze''' is huge perennial air quality and health problem stemming from [[slash and burn]] deforestation techniques coupled with expansion of []palm oil]] industry<Ref>http://world.time.com/2013/07/30/the-southeast-asian-haze-is-back-and-worse-may-follow/</ref> at the expense of new and old growth forest, driven by desires for hard currency, employment, and large profits; largely controlled by multinational corporations. This mainly occurs in the [[Indonesian]] island of [[Sumatra]] The largest of the multinational corporations responsible for the deforestation are [[Wilmar International]] and [[Cargill]].

The problem flares up every dry season, in varying degrees, and affects Malaysia, Singapore, Brunei, southern Thailand, and Indonesia. Rice paddy burning is also a common practice throughout Southeast Asia, resulting in poor air quality at a local level.

==Haze by year==
It generally refers to [[haze]] occurring in Southeast Asia; see [[Smog#Southeast Asia]]. In specific intense cases, it may refer to:
*[[1997 Southeast Asian haze]]
*[[1997 Indonesian forest fires]]
*[[2005 Malaysian haze]]
*[[2006 Southeast Asian haze]]
*[[2009 Southeast Asian haze]]
*[[2013 Southeast Asian haze]]

==See also==
*[[ASEAN Agreement on Transboundary Haze Pollution]]

==References==
{{Reflist|30em}}

{{Asia Pollution}}
{{Palm oil}}

[[Category:Southeast Asian haze| ]]

{{environmental-disaster-stub}}
{{Indonesia-stub}}

Brandrodung in Südostasien

2013-08-02T17:33:23Z

Someone not using his real name: add ref for main cause; article needs a lot of work...

{{Article for deletion/dated|page=Southeast Asian haze|timestamp=20130728151131|year=2013|month=July|day=28|substed=yes|help=off}}


{{multiple issues|
{{POV|date=July 2013}}
{{original research|date=July 2013}}
{{ref improve|date=July 2013}}
}}
{{quotebox|'''"They only have to be sparked by cigarette butts and they (peatlands) will go up in flames"|Achmad Taufik, South Sumatra Forestry Office'''<ref>{{Cite web|url=http://www.thejakartapost.com/news/2012/08/15/slash-and-burn-practices-lead-forest-fires-s-sumatra.html|title=Slash-and-burn practices lead to forest fires in S. Sumatra|first=Ansyor|last=Idrus|work=The Jakarta Post|date=15 August 2012}}</ref>}}
'''Southeast Asian haze''' is huge perennial air quality and health problem stemming from [[slash and burn]] deforestation techniques<Ref>http://world.time.com/2013/07/30/the-southeast-asian-haze-is-back-and-worse-may-follow/</ref> coupled with expansion of palm oil estates at the expense of new and old growth forest, driven by desires for hard currency, employment, and large profits; largely controlled by multinational corporations. This mainly occurs in the [[Indonesian]] island of [[Sumatra]] The largest of the multinational corporations responsible for the deforestation are [[Wilmar International]] and [[Cargill]].

The problem flares up every dry season, in varying degrees, and affects Malaysia, Singapore, Brunei, southern Thailand, and Indonesia. Rice paddy burning is also a common practice throughout Southeast Asia, resulting in poor air quality at a local level.

==Haze by year==
It generally refers to [[haze]] occurring in Southeast Asia; see [[Smog#Southeast Asia]]. In specific intense cases, it may refer to:
*[[1997 Southeast Asian haze]]
*[[1997 Indonesian forest fires]]
*[[2005 Malaysian haze]]
*[[2006 Southeast Asian haze]]
*[[2009 Southeast Asian haze]]
*[[2013 Southeast Asian haze]]

==See also==
*[[ASEAN Agreement on Transboundary Haze Pollution]]

==References==
{{Reflist|30em}}

{{Asia Pollution}}
{{Palm oil}}

[[Category:Southeast Asian haze| ]]

{{environmental-disaster-stub}}
{{Indonesia-stub}}

OZ-14 Grosa

2013-07-18T18:36:34Z

Someone not using his real name: /* Features */

{{no footnotes|date=January 2013}}
{{Infobox Weapon
|name=OTs-14 Groza
|image=[[File:ОЦ-14 4.jpg|300px]]
|caption=OTs-14-4A (configuration with grenade launcher)
|origin=[[Russian Federation]] 
|type=[[Assault rifle]]

|is_ranged=yes

|service=1994–present
|used_by=[[Spetsnaz]]
|wars=[[First Chechen War]] [[Second Chechen War]] [[2008 South Ossetia war|2008 South Ossetia War]]

|designer=V.N. Telesh and U.V. Lebedev
|design_date=1990s
|manufacturer=TsKIB SOO
|unit_cost=
|production_date=
|number=
|variants=OTs-14-4A OTs-14-4A-01 OTs-14-4A-02 OTs-14-4A-03

|spec_label=
|weight=2,7 kg (OTs-14-4A-01 and OTs-14-4A-02) 3,6 kg (OTs-14-4A and OTs-14-4A-03)
|length=610 mm (OTs-14-4A) 565 mm (OTs-14-4A-01) 500 mm (OTs-14-4A-02) 720 mm (OTs-14-4A-03)
|part_length=240 mm (Groza-4) 415 mm (Groza-1)
|width=60 mm (OTs-14-4A without a grenade launcher) 75 mm (OTs-14-4A with a grenade launcher mounted) 70 mm (OTs-14-1A without a grenade launcher) 80 mm (OTs-14-1A with a grenade launcher mounted)
|height=294 mm (OTs-14-4A without a grenade launcher) 266 mm (OTs-14-4A with a grenade launcher mounted) 350 mm (OTs-14-1A without a grenade launcher) 320 mm (OTs-14-1A with a grenade launcher mounted)

|cartridge=[[9×39mm|9x39mm]] (Groza-4), [[7.62×39mm|7.62x39mm]] (Groza-1)
|action=[[Gas-operated reloading|Gas-operated]], [[rotating bolt]]
|rate=700 rounds/min (Groza-4), 750 rounds/min (Groza-1)
|velocity=300 m/s (Groza-4), 720 m/s (Groza-1)
|range=200 m (Groza-4), 300 m (Groza-1)
|max_range=400 m (Groza-4), 500 m (Groza-1)
|feed=20-round detachable box magazine (Groza-4), 30-round detachable box magazine for (Groza-1)
|sights=Iron sights, PO4×34
}}

The '''OTs-14 Groza''' (ОЦ-14 "Гроза") is a Russian selective fire [[bullpup]] [[assault rifle]] chambered for the [[7.62×39]] round and the [[9×39mm]] subsonic round. It was developed in the 1990s at the [[TsKIB SOO]] (Central Design and Research Bureau of Sporting and Hunting Arms) in [[Tula, Russia|Tula]], Russia. The weapon is also colloquially known as OC-14 or OTs-14 "Groza" ("[[Thunderstorm]]"). The OTs-14-4A "Groza-4" has one derivative, the TKB-0239 (ТКБ-0239), also known as '''OTs-14-1A "Groza-1"''', chambered for the [[7.62×39mm|7.62x39mm]] round.

== History ==
Work on the OTs-14-4A project began in December 1992. The weapon's chief designers were Valery Telesh, responsible for the [[GP-25|GP-25 and GP-30]] under-barrel grenade launchers, and Yuri Lebedev. The team set out to design an integrated system that would incorporate all the best features of a close combat arm into a single weapon using the [[AK-74#Variants|AKS-74U]] as a starting platform. Prototypes were ready for testing in less than a year and the weapon was ready for production by early 1994.

It was first presented to the public at the MILIPOL [[Moscow]] trade show in April 1994 and adopted by the [[Ministry of Internal Affairs (Russia)|Ministry of Internal Affairs (MVD)]] shortly thereafter. The success of the OTs-14-4A in the hands of MVD personnel brought it to the attention of the [[Ministry of Defence (Russia)|Ministry of Defence (MO)]], who also had a requirement for such a weapon. After a period of testing, the weapon was adopted for [[spetsnaz]] forces and some airborne and specialist front-line combat units such as [[combat engineer]]s. The weapon was originally intended to have used any one of four cartridges: [[5.45×39mm|5.45x39mm]], [[5.56×45mm NATO|5.56x45mm]], [[7.62×39mm|7.62x39mm]] or [[9×39mm|9x39mm]]. That idea was dropped and the assault rifle was originally chambered in 9x39mm to meet the MVD's requirement for a close combat weapon for deployment in [[Chechnya]].

== Design details ==
=== Operating mechanism ===
The OTs-14-4A is a small arms weapon system based on the 5.45x39mm AKS-74U [[carbine]]. It is a [[selective fire]], air-cooled magazine-fed rifle with a [[Gas-operated reloading|gas-actuated]] piston operating system and a [[rotating bolt|rotary bolt]] locking mechanism.

=== Features ===
The OTs-14-4A shares a 75% component commonality with the AKS-74U.{{cn}} The basic components of the weapon are borrowed directly from the AKS-74U assault rifle and slightly modified, simplifying the design as a whole and making the weapon considerably cheaper. The weapon has modular design allowing for assembly of one of four weapon versions depending on the assigned mission. It is configured in a bullpup layout for increased portability and balance. The grip is displaced forward, making the assault rifle compact, suitable for concealed carrying and so well balanced that it can be fired using just one hand, like a pistol.

The weapon fires from a [[closed bolt]] and has a hammer-type firing mechanism. It has a unitary trigger; a three-position combination fire mode selector switch / manual safety on the left side of the receiver sets whether it fires either the rifle or the grenade launcher or places it in "safe". The assault rifle is equipped with [[iron sight]]s contained in the carrying handle that consist of an adjustable rear aperture sight on a tangent leaf with range graduations from 50 to 200 m, and a forward post. The grenade launcher is aimed using a folding leaf sight. The weapon will also accept several optical sights, including the [[PSO-1|PSO]] telescopic sights which mount directly onto the carrying handle or, as on early models, onto a bracket on the left side of the [[Receiver (firearms)|receiver housing]]. The OTs-14-4A also has a night sight dovetail that will accept all standard night vision optics.

=== Accessories ===
It is issued in an [[aluminum]] transport case with equipment and accessories for a wide array of tactical situations. Included in the case are two different grip and trigger assemblies, one for use with the modified GP-25/30 grenade launcher and another for use when the launcher is detached. When the grenade launcher is installed, the combined rifle and grenade launcher is operated with a single trigger. A selector switch on left side of the grip near the trigger guard allows the user to select between rifle or grenade barrels. When the grenade launcher is detached, it is replaced by a vertical grip. A [[suppressor]] is also included in the standard kit, as is a quick-change short barrel for use with the suppressor or for when maximum compactness is desired.

=== Variants ===
* '''OTs-14-1A 7.62/40''' '''''Groza-1''''' - Primary model chambered in 7.62x39mm M43 Soviet; it uses the same magazines as the AK-47 / AKM assault rifles. It has a long barrel and a [[GP-25]] under-barrel grenade launcher. Originally an experimental chambering, it was later adopted by the Army for use by its Airborne and Spetsnaz troops. It has more hitting power and range than the subsonic version and can use cheaper ammunition readily available from supplies.
** '''OTs-14-1A-01''' - Carbine Variant with a short barrel and a vertical foregrip.
** '''OTs-14-1A-02''' - Special Carbine Variant with a short barrel threaded for a suppressor.
** '''OTs-14-1A-03''' - Special Sniper Variant with a short barrel threaded for a suppressor and a telescopic sight bracket on the carrying handle / iron sights.
 
* '''OTs-14-2A''' - Experimental model chambered in 5.54x39mm M74 Soviet. Not adopted due to a lack of hitting power in comparison with the 7.62mm Soviet and 9mm Subsonic models.
 
* '''OTs-14-3A''' - Experimental model chambered in 5.56x45mm NATO. Neither adopted nor put into production due to a lack of interest from the domestic military or the firm's foreign customers.
 
* '''OTs-14-4A 9/40''' '''''Groza-4''''' - Primary model chambered in 9x39mm Subsonic; it uses the same 20-round magazines as the [[VSS Vintorez|VSS ''Vintorez'' ("Thread-cutter")]] and [[AS Val|AS ''Val'' ("Shaft")]]. It has a long barrel and a [[GP-25]] under-barrel grenade launcher.
** '''OTs-14-4A-01''' - Carbine Variant with a short barrel and a vertical foregrip.
** '''OTs-14-4A-02''' - Special Carbine Variant with a short barrel threaded for a suppressor.
** '''OTs-14-4A-03''' - Special Sniper Variant with a short barrel threaded for a suppressor and a telescopic sight bracket on the carrying handle / iron sights.

<gallery>
File:ОЦ-14 4.jpg|
File:ОЦ-14 2.jpg| ''OTs-14-4A-01''
File:ОЦ-14 3.jpg| ''OTs-14-4A-02''
File:ОЦ-14 Гроза.jpg| ''OTs-14-4A-03''
</gallery>

=== Advantages ===
* Weapon compactness, relatively small weight and bullpup layout provided a good balance and reduced barrel jump.
* It is as reliable as the [[Kalashnikov assault rifle]], as it is based on the same internal design.
* [[9×39mm|9x39mm]] SP-5 and SP-6 subsonic rounds, along with the attachable suppressor, provide very silent shooting.
* Heavy 9 mm bullet (16 g) provides high stopping power and lethality.
* Good accuracy, along with the high damage and penetration of bullets and a decent rate of fire, provides a reliable engagement of the targets in bulletproof vests of third-class protection, and targets behind cover.
* Modular design allows you to convert the complex into an assault rifle, a [[CQB]] assault rifle, a grenade launcher and a sniper rifle.
* The 9x39mm rounds' subsonic velocity actually makes them surprisingly viable for CQB situations, and the Groza is no exception.

=== Disadvantages ===
[[File:Beslan-spetznaz.jpg|thumb|Member of an unidentified Russian special force carrying suppressed OC-14 (on his back) during the [[Beslan school hostage crisis]] in 2004]]

* Short aiming line make aiming problematic. Curved trajectory of the [[9×39mm|9x39mm]] round makes it difficult to choose the aiming point.
* Bullpup frame causes difficulties with changing of the magazine.
* The 9x39mm Subsonic version has a low capacity 20-round magazine.
* Using of a single trigger for both assault rifle and grenade launcher slows down switching from grenade launcher to assault rifle and back.
* The side-mounts for different optics must be set up additionally.
* Variants without grenade launcher have a shifted gravity center.
* Left-handed shooting is impossible, because of an extractor situated close to the face on the right side of the weapon.
* The gravity center is situated in the pistol grip and loads the right hand, that lessens the accuracy.

=== See also ===

== See also ==
*[[List of Russian weaponry]]

== References ==
* [http://www.sinopa.ee/sor/bo001/bo04av/bo04av05/oc14.htm Project "Groza"]
* [http://www.enemyforces.com/firearms/groza.htm EnemyForces]
* [http://world.guns.ru/assault/as09-e.htm Modern Firearms]
* [http://weapon.at.ua/load/321-1-0-815 Энциклопедия Оружия: Автоматно-гранатометный комплекс ОЦ-14 «Гроза» (Encyclopedia of Weapons: Assault Rifle / Grenade Launcher System OTs-14 ''Groza'' ("Storm"))]
*{{cite book| last = Cutshaw| first = Charlie| authorlink = | coauthors = | year = 1998| chapter =| title = The New World of Russian Small Arms & Ammo| publisher = Paladin Press| location = Boulder, CO| isbn = 0-87364-993-1|pages=21-26}}

{{AK47 derivatives}}
{{Bullpup Firearms}}

[[Category:7.62 mm firearms]]
[[Category:Assault rifles]]
[[Category:Bullpup firearms]]
[[Category:Kalashnikov derivatives]]
[[Category:Weapons of Russia]]

Leben auf dem Mars

2013-07-16T15:13:41Z

Someone not using his real name: /* Viking experiments */ rebuttal of 1st Navarro-González

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious|date=July 2013}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref><ref name="PlaxcoGross2011_2"/>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412">{{cite web |last=Klotz |first=Irene |title=Mars Viking Robots 'Found Life' |url=http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |date=12 April 2012 |publisher=[[Discovery Channel|DiscoveryNews]] |accessdate=16 April 2012 }}</ref>

A research team from the [[National Autonomous University of Mexico]] headed by [[Rafael Navarro-González]], concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> [[Klaus Biemann]], the principal investigator of the GCMS experiment on ''Viking'' wrote a rebuttal.<Ref>{{cite journal
| title = On the ability of the Viking gas chromatograph–mass spectrometer to detect organic matter
| last = Biemann
| first = Klaus
| journal = Proceedings of the National Academy of Sciences of the United States of America
| volume = 104
| issue = 25
| pages = 10310–10313
| year = 2007
| doi = 10.1073/pnas.0703732104
| pmid = 17548829
| pmc = 1965509
|bibcode = 2007PNAS..10410310B }}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

After the discovery of [[perchlorate]]s on Mars by the [[Phoenix (spacecraft)|Phoenix lander]], practically the same team of Navarro-González published a paper arguing that the Viking GCMS results were compromised by presence of perchlorates.<ref name=Webster>Webster, Guy; Hoover, Rachel; Marlaire, Ruth; Frias, Gabriela (2010-09-03). "[http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 Missing Piece Inspires New Look at Mars Puzzle]". NASA Jet Propulsion Laboratory. Retrieved 2010-10-24.</ref> A 2011 astrobiology textbook notes that "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283|edition=2nd}}</ref> Biemann has written a commentary critical of this Navarro-González paper as well,<ref>{{doi|10.1029/2011JE003869}}</ref> to which the latter have replied;<ref>{{doi|10.1029/2011JE003880}}</ref> the exchange was published in December 2011.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]].<ref name="Levin"/>. The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
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{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

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Leben auf dem Mars

2013-07-16T13:21:16Z

Someone not using his real name: /* Gillevinia straata */ actually he doesn't mention "Gillevinia straata" either, and his low-quality two-page pamphlet was not noted by independent sources. Removing per WP:UNDUE

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref><ref name="PlaxcoGross2011_2"/>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by [[Rafael Navarro-González]], concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

After the discovery of [[perchlorate]]s on Mars by the [[Phoenix (spacecraft)|Phoenix lander]] , practically the same team of Navarro-González published a paper arguing that the Viking GCMS results were compromised by presence of perchlorates.<ref name=Webster>Webster, Guy; Hoover, Rachel; Marlaire, Ruth; Frias, Gabriela (2010-09-03). "[http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 Missing Piece Inspires New Look at Mars Puzzle]". NASA Jet Propulsion Laboratory. Retrieved 2010-10-24.</ref> A 2011 astrobiology textbook notes that "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283|edition=2nd}}</ref> [[Klaus Biemann]], the principal investigator of the GCMS experiment on ''Viking'' has written a commentary critical of the Navarro-González paper,<ref>{{doi|10.1029/2011JE003869}}</ref> to which the latter have replied;<ref>{{doi|10.1029/2011JE003880}}</ref> the exchange was published in December 2011.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]].<ref name="Levin"/>. The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

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Leben auf dem Mars

2013-07-16T13:18:34Z

Someone not using his real name: /* Gillevinia straata */ WP:SYNT as they don't mention "Gillevinia straata"

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref><ref name="PlaxcoGross2011_2"/>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by [[Rafael Navarro-González]], concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

After the discovery of [[perchlorate]]s on Mars by the [[Phoenix (spacecraft)|Phoenix lander]] , practically the same team of Navarro-González published a paper arguing that the Viking GCMS results were compromised by presence of perchlorates.<ref name=Webster>Webster, Guy; Hoover, Rachel; Marlaire, Ruth; Frias, Gabriela (2010-09-03). "[http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 Missing Piece Inspires New Look at Mars Puzzle]". NASA Jet Propulsion Laboratory. Retrieved 2010-10-24.</ref> A 2011 astrobiology textbook notes that "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283|edition=2nd}}</ref> [[Klaus Biemann]], the principal investigator of the GCMS experiment on ''Viking'' has written a commentary critical of the Navarro-González paper,<ref>{{doi|10.1029/2011JE003869}}</ref> to which the latter have replied;<ref>{{doi|10.1029/2011JE003880}}</ref> the exchange was published in December 2011.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
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{{Extraterrestrial life}}
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{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

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Leben auf dem Mars

2013-07-16T13:11:46Z

Someone not using his real name: /* Viking experiments */ added the perchlorate controversy

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref><ref name="PlaxcoGross2011_2"/>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by [[Rafael Navarro-González]], concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

After the discovery of [[perchlorate]]s on Mars by the [[Phoenix (spacecraft)|Phoenix lander]] , practically the same team of Navarro-González published a paper arguing that the Viking GCMS results were compromised by presence of perchlorates.<ref name=Webster>Webster, Guy; Hoover, Rachel; Marlaire, Ruth; Frias, Gabriela (2010-09-03). "[http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 Missing Piece Inspires New Look at Mars Puzzle]". NASA Jet Propulsion Laboratory. Retrieved 2010-10-24.</ref> A 2011 astrobiology textbook notes that "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283|edition=2nd}}</ref> [[Klaus Biemann]], the principal investigator of the GCMS experiment on ''Viking'' has written a commentary critical of the Navarro-González paper,<ref>{{doi|10.1029/2011JE003869}}</ref> to which the latter have replied;<ref>{{doi|10.1029/2011JE003880}}</ref> the exchange was published in December 2011.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

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Leben auf dem Mars

2013-07-16T12:59:31Z

Someone not using his real name: /* Viking experiments */

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref><ref name="PlaxcoGross2011_2"/>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by Rafael Navarro-González, concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

{{Link GA|ca}}
{{Link GA|ja}}
{{Link FA|sh}}

Leben auf dem Mars

2013-07-16T12:57:57Z

Someone not using his real name: /* Viking experiments */

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [[Gas chromatography–mass spectrometry|GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by Rafael Navarro-González, concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
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{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

{{Link GA|ca}}
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Leben auf dem Mars

2013-07-16T12:57:13Z

Someone not using his real name: /* Viking experiments */ fixing somewhat biased summary

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result,{{dubious}} showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the [Gas chromatography–mass spectrometry|[GCMS]] detected no organic molecules. However, there are vastly different interpretations of what those results imply.

A 2011 [[astrobiology]] textbook notes that the GCMS was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA282|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=282–283}}</ref>

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> Levin's interpretation is disputed by many scientists.<ref name="cnn">Richard Stenger [http://edition.cnn.com/2000/TECH/space/11/07/mars.sample/ Mars sample return plan carries microbial risk, group warns], CNN, November 7, 2000</ref> A 2006 [[astrobiology]] textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food. This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas."<ref name="Plaxco2006">{{cite book|author=Kevin W. Plaxco and Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=OjYSAA5oHdcC&pg=PA223|year=2006|publisher=JHU Press|isbn=978-0-8018-8366-8|page=223}}</ref> Other scientists argue that [[superoxide]]s in the soil could have produced this effect without life being present.<ref name="PlaxcoGross2011_2">{{cite book|author1=Kevin W. Plaxco|author2=Michael Gross|title=Astrobiology: A Brief Introduction|url=http://books.google.com/books?id=x83omgI5pGQC&pg=PA285|year=2011|publisher=JHU Press|isbn=978-1-4214-0194-2|pages=285–286|edition=2nd}}</ref> An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

A research team from the [[National Autonomous University of Mexico]] headed by Rafael Navarro-González, concluded that the GCMS equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

=== ''Gillevinia straata'' ===
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

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Leben auf dem Mars

2013-07-16T12:35:06Z

Someone not using his real name: /* Viking experiments */ has nothing to do with that term as used in computer science; correction and replaced crap news source with more informed one

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result, showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the GC-MS detected no organic molecules. However, there are vastly different interpretations of what those results imply.

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> However, this result is disputed by many scientists, who argue that [[superoxidant]] chemicals in the soil could have produced this effect without life being present. An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=[[International Journal of Aeronautical and Space Sciences]] |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[cluster analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref>[http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ Life on Mars Found by NASA's Viking Mission?]</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

A research team from the [[National Autonomous University of Mexico]] headed by Rafael Navarro-González, concluded that the equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

==== ''Gillevinia straata'' ====
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

{{Link GA|ca}}
{{Link GA|ja}}
{{Link FA|sh}}

Leben auf dem Mars

2013-07-16T12:06:11Z

Someone not using his real name: /* Gillevinia straata */ Levin is not a professor

{{Other uses}}
[[File:TerraformedMars.jpg|thumb|An artist's impression of what Mars' surface and atmosphere might look like, if Mars were [[Terraforming of Mars|terraformed]].]]
[[File:TerraformedMarsGlobeRealistic.jpg|thumb|Another view of a terraformed Mars]]

For centuries people have speculated about the possibility of '''life on Mars''' knowing to the planet's proximity and similarity to [[Earth]]. Serious searches for evidence of life began in the 19th century, and continue via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and the search for [[biomarker]] gases in the atmosphere.<ref>{{cite conference |url=http://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX}}</ref>

Mars is of particular interest for the study of the origins of life, because of its similarity to the early Earth. This is especially so as Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], and has remained pretty much unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars' surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |year=1989 |last1=McKay |first1=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214}}</ref><ref name='Fromproto'>{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last1=Gaidos |first1=Eric |last2=Selsis |first2=Franck |year=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> It remains an open question whether life currently exists on Mars, or has existed there in the past, and fictional [[Martian]]s have been a recurring feature of [[popular entertainment]] of the 20th and 21st centuries.

==Early speculation==
{{Double image|right|Karte Mars Schiaparelli MKL1888.png|220|Lowell Mars channels.jpg|220|Historical map of Mars from [[Giovanni Schiaparelli]].|Mars canals illustrated by astronomer [[Percival Lowell]], 1898.}}
[[Geology of Mars|Mars' polar ice caps]] were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by [[William Herschel]] in the latter part of the 18th century. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to Earth, for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does — but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to the increase in speculation that the darker [[albedo feature]]s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some form of life.

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canal]]s — which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906, proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |year=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation.

[[Spectroscopy|Spectroscopic]] analysis of Mars' atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{Cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |year=1999 |isbn=0-7137-2747-0}}{{page needed|date=June 2013}}</ref> By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.

==Habitability==
Chemical, physical, geological and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.<ref name='2013 LPS'>{{cite journal |bibcode=2013LPICo1719.2185C |title=Habitability Assessment at Gale Crater: Implications from Initial Results |last1=Conrad |first1=P. G. |last2=Archer |first2=D. |last3=Coll |first3=P. |last4=De La Torre |first4=M. |last5=Edgett |first5=K. |last6=Eigenbrode |first6=J. L. |last7=Fisk |first7=M. |last8=Freissenet |first8=C. |last9=Franz |first9=H. |volume=1719 |year=2013 |pages=2185 |journal=44th Lunar and Planetary Science Conference}}</ref> The two current ecological approaches for predicting the potential habitability of the Martian surface use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from Solar ultraviolet and [[Cosmic ray|galactic cosmic radiation]].<ref name='D.C.Golden'>{{cite journal |bibcode=2012P&SS...72...91S |title=Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial colonies and survival under Martian conditions |last1=Schuerger |first1=Andrew C. |last2=Golden |first2=D. C. |last3=Ming |first3=Doug W. |volume=72 |issue=1 |year=2012 |pages=91–101 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.07.026}}</ref><ref name=Beaty>{{cite journal |bibcode=2006AsBio...6..677M |title=Findings of the Mars Special Regions Science Analysis Group |author1=MEPAG Special Regions-Science Analysis Group |last2=Beaty |first2=D. |last3=Buxbaum |first3=K. |last4=Meyer |first4=M. |last5=Barlow |first5=N. |last6=Boynton |first6=W. |last7=Clark |first7=B. |last8=Deming |first8=J. |last9=Doran |first9=P. T. |volume=6 |year=2006 |pages=677–732 |journal=Astrobiology |doi=10.1089/ast.2006.6.677 |pmid=17067257 |issue=5}}</ref>

Scientists do not know the minimum number of parameters for determination of habitability potential, but they are certain it is greater than one or two of the factors in the table below.<ref name='2013 LPS'/> Similarly, for each group of parameters, the habitability threshold for each is to be determined.<ref name='2013 LPS'/> Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.<ref name='dust-up'>{{cite web | url = http://www.astrobio.net/exclusive/3495/mars-contamination-dust-up | title = Mars Contamination Dust-Up | accessdate = 2013-07-04 | first = Charles Q. Choi, | date = 17 May 2010 | publisher = Astrobiology Magazine | quote = Whenever multiple biocidal factors are combined, the survival rates plummet quickly,}}</ref> There are no full-Mars simulations published yet that include all of the biocidal factors combined.<ref name='dust-up'/>

{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Some habitability factors'''<ref name=Beaty/>
|-
|[[Water on Mars|Water]] || {{·}} [[Water activity|liquid water activity]] (aw) {{·}} Past/future liquid (ice) inventories {{·}} [[Salinity]], [[pH]], and [[Reduction potential|Eh]] of available water
|-
|Chemical environment|| '''Nutrients:''' {{·}} C, H, N, O, P, S, essential metals, essential micronutrients {{·}}[[Nitrogen fixation|Fixed nitrogen]] {{·}}Availability/mineralogy '''Toxin abundances and lethality:''' {{·}} [[Heavy metal (chemistry)|Heavy metals]] (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels) {{·}} Globally distributed oxidizing soils
|-
|Energy for [[metabolism]]|| '''Solar''' (surface and near-surface only) '''Geochemical''' (subsurface) {{·}} [[Oxidizing agent|Oxidants]] {{·}} [[Reducing agent|Reductants]] {{·}} [[Redox gradient]]s
|-
|Conducive physical conditions || {{·}}Temperature {{·}}Extreme diurnal temperature fluctuations {{·}}Low pressure (Is there a low-pressure threshold for terrestrial [[Anaerobic organism|anaerobes]]?) {{·}}Strong [[ultraviolet germicidal irradiation]] {{·}}[[Cosmic ray|Galactic cosmic radiation]] and [[Solar proton event|solar particle event]]s (long-term accumulated effects) {{·}} Solar UV-induced volatile oxidants, e.g., [[Superoxide|O 2–]], O–, [[Hydrogen peroxide|H2O2]], O3 {{·}}Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations) {{·}}Substrate (soil processes, rock microenvironments, dust composition, shielding) {{·}}High [[Carbon dioxide|CO2]] concentrations in the global atmosphere {{·}}Transport ([[Aeolian processes|aeolian]], ground water flow, surface water, glacial)
|-
|}

===Past===
The loss of the Martian [[magnetosphere|magnetic field]] strongly affected surface environments through atmospheric loss and increased radiation; this change significantly degraded surface habitability.<ref name='Biosignatures 2011'/> When there was a magnetic field, the atmosphere would have been protected from erosion by [[solar wind]], which would ensure the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars.<ref name='Dehant'>{{cite book |doi=10.1007/978-0-387-74288-5_10 |chapter=Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars |title=Geology and Habitability of Terrestrial Planets |series=Space Sciences Series of ISSI |year=2007 |last1=Dehant |first1=V. |last2=Lammer |first2=H. |last3=Kulikov |first3=Y. N. |last4=Grießmeier |first4=J. -M. |last5=Breuer |first5=D. |last6=Verhoeven |first6=O. |last7=Karatekin |first7=Ö. |last8=Hoolst |first8=T. |last9=Korablev |first9=O. |isbn=978-0-387-74287-8 |volume=24 |pages=279–300}}</ref>

Soil and rock samples studied in 2013 by NASA's [[Curiosity rover]]'s onboard instruments brought about additional information on several habitability factors.<ref name='ancient life'>{{cite news | title = NASA Rover Finds Conditions Once Suited for Ancient Life on Mars | date = 12 March 2013 | url = http://www.nasa.gov/mission_pages/msl/news/msl20130312.html | work = NASA | accessdate = 2013-06-06}}</ref> The rover team identified some of the key chemical ingredients for life in this soil, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as well as clay minerals, suggesting a long-ago aqueous environment — perhaps a lake or an ancient streambed — that was neutral and not too salty.<ref name='ancient life'/> The confirmation that liquid water once flowed on Mars, the existence of nutrients, and the previous discovery of a past [[magnetosphere|magnetic field]] that protected the planet from cosmic and Solar radiation,<ref>{{cite web | url=http://www.nasa.gov/centers/goddard/news/topstory/2005/mgs_plates.html | title=New Map Provides More Evidence Mars Once Like Earth | publisher=NASA | work=Goddard Space Flight Center | date=October 12, 2005 | accessdate=5 June 2013 | author= Neal-Jones, Nancy | coauthor =O'Carroll, Cynthia}}</ref><ref>{{Cite web| title=Martian Interior: Paleomagnetism |publisher=European Space Agency |work=Mars Express |date=4 January 2007 |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31028&fbodylongid=645}}</ref> together strongly suggest that Mars could have had the environmental factors to support life.<ref name='Wall'/> However, the assessment of past habitability is not in itself evidence that Martian life has ever actually existed. If it did, it was likely [[microorganism|microbial]], existing communally in fluids or on sediments, either free-living or as [[biofilm]]s, respectively.<ref name='Biosignatures 2011'/>

===Present===
No definitive evidence for biosignatures or organics of Martian origin has been identified, and assessment will continue not only through the Martian seasons, but also back in time as the ''Curiosity'' rover studies what is recorded in the depositional history of the rocks in Gale Crater.<ref name='2013 LPS'/> While the ''Curiosity'' has not identified the minimum number of parameters for determination of habitability potential, other teams have proposed hypotheses based on simulations.

====Subsurface====

Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,<ref name='2013 LPS'/> life on the surface of Mars is extremely unlikely because it is bathed in radiation and it is completely frozen.<ref name='cosmic radiation'/><ref name="Dartnell"/><ref name='DartnellGeographic'/><ref name='Dartnell-1'/><ref name='ionising radiation'/><ref name='Parnell'>{{cite news | first = JohnThomas Didymus | title = Scientists find evidence Mars subsurface could hold life | date = 21 January | url = http://digitaljournal.com/article/341801 | work = Digital Journal - Science | accessdate = 2013-06-05 | quote = There can be no life on the surface of Mars because it is bathed in radiation and it's completely frozen. However, life in the subsurface would be protected from that. - Prof. Parnell.}}</ref> Therefore, the best potential locations for discovering life on Mars may be at subsurface environments that have not been studied yet.<ref name='Biosignatures 2011'>{{cite journal |doi=10.1089/ast.2010.0506 |quote=There is general consensus that extant microbial life on Mars would likely exist (if at all) in the subsurface and at low abundance. |title=Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group |year=2011 |last1=Summons |first1=Roger E. |last2=Amend |first2=Jan P. |last3=Bish |first3=David |last4=Buick |first4=Roger |last5=Cody |first5=George D. |last6=Des Marais |first6=David J. |last7=Dromart |first7=Gilles |last8=Eigenbrode |first8=Jennifer L. |last9=Knoll |first9=Andrew H. |journal=Astrobiology |volume=11 |issue=2 |pages=157–81 |pmid=21417945}}</ref><ref name='Parnell'/><ref name=Steigerwald/><ref>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html NASA - Mars Rovers Sharpen Questions About Livable Conditions]</ref><ref>{{cite news | title = Mars: 'Strongest evidence' planet may have supported life, scientists say | date = 20 January 2013 | url = http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-21063817 | work = BBC News | accessdate = 2013-01-22}}</ref><ref>{{cite journal |doi=10.1038/ngeo1706 |title=Groundwater activity on Mars and implications for a deep biosphere |year=2013 |last1=Michalski |first1=Joseph R. |last2=Cuadros |first2=Javier |last3=Niles |first3=Paul B. |last4=Parnell |first4=John |last5=Deanne Rogers |first5=A. |last6=Wright |first6=Shawn P. |journal=Nature Geoscience |volume=6 |issue=2 |pages=133–8}}</ref> The extensive [[Volcanology of Mars|volcanism]] in the past, possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large [[aquifer]]s with deposits of saline liquid water, minerals, organic molecules, and [[Geothermal gradient|geothermal heat]] – potentially providing a habitable environment away from the harsh surface conditions.<ref name='Parnell'/><ref name='subsurface habitability model'>{{cite journal |bibcode=2012LPI....43.2943D |quote=The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth. |title=A Possible Biogeochemical Model for Mars |last1=De Morais |first1=A. |volume=43 |year=2012 |pages=2943 |journal=43rd Lunar and Planetary Science Conference}}</ref><ref>{{cite news | first = Paul S. | last = Anderson | title = New Study Says Large Regions of Mars Could Sustain Life | date = 15 December 2011 | url = http://www.universetoday.com/91848/new-study-says-large-regions-of-mars-could-sustain-life/ | work = Universe Today | accessdate = 2013-06-05 | quote = Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. }}</ref><ref>{{cite web | url = http://phoenix.lpl.arizona.edu/mars143.php | title = Habitability and Biology: What are the Properties of Life? | accessdate = 2013-06-06 | work = Phoenix Mars Mission | publisher = The University of Arizona | quote= If any life exists on Mars today, scientists believe it is most likely to be in pockets of liquid water beneath the Martian surface.}}</ref>

====Surface brines====

Although liquid water does not appear at the surface of Mars,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |quote=In summary, on present-day Mars, liquid water is unlikely except as the result of a quick and dramatic change in environmental conditions such as from a landslide that exposes buried ice to sunlight (Costard et al. 2002), or from the introduction of an artificial heat source. |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83–96 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref><ref name=Haberle>{{cite journal |last1=Haberle |first1=Robert M. |last2=McKay |first2=Christopher P. |last3=Schaeffer |first3=James |last4=Cabrol |first4=Nathalie A. |last5=Grin |first5=Edmon A. |last6=Zent |first6=Aaron P. |last7=Quinn |first7=Richard |title=On the possibility of liquid water on present-day Mars |doi=10.1029/2000JE001360 |journal=Journal of Geophysical Research: Planets |volume=106 |issue=El0 |year=2001 |pages=23317–26 |bibcode=bibcode=2001JGR...10623317H |quote=Introduction: The mean annual surface pressure and temperature on present-day Mars do not allow for the stability of liquid water on the surface. [...] Conclusion: It is possible, even likely, that solar-heated liquid water never forms on present-day Mars.}}</ref> several modeling studies suggest that potential locations on Mars could include regions where thin films of salty liquid [[brine]] or [[perchlorate]] may form near the surface<ref name=Haberle/><ref name=Haberle/><ref name='2013 conference'>{{cite web | url = http://planets.ucla.edu/meetings/mars-habitability-2013/program/ | title = Conference: The Present-Day Habitability of Mars 2013 | accessdate = 2013-06-17 | date = February 4–6, 2013 | format = PDF | publisher = The UCLA Institute for Planets and Exoplanets}}</ref> that may provide a potential location for terrestrial salt and cold-loving microorganisms ([[halophile]] [[psychrophilic]]).<ref>{{cite journal |doi=10.1080/08120099.2011.591430 |title=Using the phase diagram of liquid water to search for life |year=2012 |last1=Jones |first1=E. G. |last2=Lineweaver |first2=C. H. |journal=Australian Journal of Earth Sciences |volume=59 |issue=2 |pages=253–62}}</ref> Various salts present in the Martian soil may act as an antifreeze and could keep water liquid well below its normal freezing point, if water was present at certain favorable locations.<ref name=Haberle/><ref name=Lobitz>{{cite journal | doi = 10.1073/pnas.031581098 | last1 = Lobitz | first1 = B. | last2 = Wood | year = 2001 | first2 = BL | last3 = Averner | first3 = MM | last4 = McKay | first4 = CP | title = Use of spacecraft data to derive regions on Mars where liquid water would be stable | journal=Proc. Natl. Acad. Sci. | volume = 98 | issue = 5| pages = 2132–2137 | pmid = 11226204 | pmc = 30104 |bibcode = 2001PNAS...98.2132L |quote= These results do not indicate that water is present at these locations, only that, if it were present and heat sources were sufficient to bring the water in thermal equilibrium with the surface, the resulting liquid would be stable against freezing or boiling.}}</ref><ref name='Parro 2011'>{{cite journal | title = A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars | journal = Astroiology | date = December 2011 | first = Victor Parro | coauthors = Graciela de Diego-Castilla, Mercedes Moreno-Paz, Yolanda Blanco, Patricia Cruz-Gil, José A. Rodríguez-Manfredi, David Fernández-Remolar, Felipe Gómez, Manuel J. Gómez, Luis A. Rivas, Cecilia Demergasso, Alex Echeverría, Viviana N. Urtuvia, Marta Ruiz-Bermejo, Miriam García-Villadangos, Marina Postigo, Mónica Sánchez-Román, Guillermo Chong-Díaz, and Javier Gómez-Elvira. | volume = 11 | issue = 10 | pages = 969–996 | doi = 10.1089/ast.2011.0654 | url = http://online.liebertpub.com/doi/abs/10.1089/ast.2011.0654 | format = PDF | accessdate = 2013-06-30}}</ref> Astrobiologists are keen to find out more, as not much is known about these brines at the moment. The briny water may or may not be habitable to microbes from Earth or Mars.<ref>{{cite web |url=http://www.space.com/19928-mars-habitable-life-possible.html |title= Mars May Be Habitable Today, Scientists Say|author=Rod Pyle |date= 25 February 2013|work= space.com}}</ref> Another researcher argues that although chemically important, thin films of transient liquid water are not likely to provide suitable sites for life.<ref name=Lobitz/> In addition, an astrobiology team asserted that the [[Water activity|activity of water]] on salty films, the temperature, or both are less than the biological thresholds across the entire Martian surface and shallow subsurface.<ref name=Beaty/>

The damaging effect of [[ionizing radiation]] on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats.<ref name='Dartnell-1'>{{cite journal |bibcode=2007GeoRL..3402207D |doi=10.1029/2006GL027494 |quote=The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2}}</ref><ref name='ionising radiation'>{{cite journal | title = Martian sub-surface ionising radiation: biosignatures and geology | journal = Biogeosciences | year = 2007 | first1 = L. R. |last1=Dartnell |first2=L. |last2=Desorgher |first3=J. M. |last3=Ward |first4=A. J. |last4=Coates | volume = 4 | pages = 545–558 | doi = 10.5194/bg-4-545-2007 | bibcode = 2007BGeo....4..545D | quote = This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs. | issue = 4}}</ref><ref>{{citation | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | contribution = Implications of cosmic radiation on the Martian surface for microbial survival and detection of fluorescent biosignatures | title = 42nd Lunar and Planetary Science Conference | publisher = Lunar and Planetary Institute | place = The Woodlands, Texas | date = March 7–11, 2011 | contribution-url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-06-30}}</ref> Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs.<ref name='ionising radiation'/> Also, solar ultraviolet (UV) radiation proved particularly devastating for the survival of cold-resistant microbes under simulated surface conditions on Mars, as UV radiation was readily and easily able to penetrate the salt-organic matrix that the bacterial cells were embedded in.<ref name='Scarce shelter'>{{cite journal | title = Scarce Shelter on Mars | journal = Astrobiology Magazine | date = 1 June 2009 | first = Jeremy Hsu | url = http://www.astrobio.net/exclusive/3144/scarce-shelter-on-mars | accessdate = 2013-07-04}}</ref> In addition, NASA's [[Mars Exploration Program]] states that life on the surface of Mars is unlikely, given the presence of [[superoxide]]s that break down organic (carbon-based) molecules on which life is based.<ref>{{cite web | url = http://mars.jpl.nasa.gov/programmissions/science/goal1/ | title = Goal 1: Determine if Life Ever Arose On Mars | accessdate = 2013-06-29 | first = The Mars Exploration Program | work = NASA}}</ref>

===Cosmic radiation===
In 1965, the [[Mariner 4]] probe discovered that Mars had no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic radiation]] and [[solar radiation]]; observations made in the late 1990s by the Mars Global Surveyor confirmed this discovery.<ref>{{cite book |chapterurl=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/ |chapter=Mars: Magnetic Field and Magnetosphere |first1=J. G. |last1=Luhmann |first2=C. T. |last2=Russell |title=Encyclopedia of Planetary Sciences |editor1-first=J. H. |editor1-last=Shirley |editor2-first=R. W. |editor2-last=Fainbridge |pages=454–6 |publisher=Chapman and Hall |location=New York |year=1997}}</ref> Scientists speculate that the lack of magnetic shielding helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.<ref>{{cite web |url=http://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/ |title=The Solar Wind at Mars |date=January 31, 2001 |first=Tony |last=Phillips |publisher=NASA}}</ref> As a result, the planet has been vulnerable to radiation from space for about 4 billion years.<ref name='hostile to life'>{{cite news | title = What makes Mars so hostile to life? | date = 7 January 2013 | url = http://www.bbc.co.uk/science/0/20915340 | work = BBC News | accessdate = 2013-06-15}}</ref> Currently, ionizing radiation on Mars is typically two orders of magnitude (or 100 times) higher than on Earth.<ref>{{cite journal | title = The impact of Mars geological evolution in high energy ionizing radiation environment through time | journal = Planetary and Space Science - Eslevier | date = November 2012 | first = A. Keating | coauthors = P. Goncalves | volume = 72 | issue = 1 | pages = 70–77 | url = http://www.sciencedirect.com/science/article/pii/S0032063312001225 | accessdate = 2013-06-28}}</ref> Even the hardiest cells known could not possibly survive the cosmic radiation near the surface of Mars for that long.<ref name='cosmic radiation'/><ref>{{cite journal | title = IMPLICATIONS OF COSMIC RADIATION ON THE MARTIAN SURFACE FOR MICROBIAL SURVIVAL AND DETECTION OF FLUORESCENT BIOSIGNATURES. | journal = Lunar and Planetary Institute | year = 2011 | first = Lewis R. Dartnell | coauthors = Michael C. Storrie-Storrie-Lombardi, Jan-Peter. Muller, Andrew. D. Griffiths, Andrew J. Coates, John M. Ward | url = http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1977.pdf | format = PDF | accessdate = 2013-07-04}}</ref> After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several meters of the planet's surface would be killed by lethal doses of cosmic radiation.<ref name='cosmic radiation'>{{cite web | url = http://www.space.com/3396-study-surface-mars-devoid-life.html | title = Study: Surface of Mars Devoid of Life | accessdate = 28 May 2013 | first = Ker Than | date = 29 January 2007 | work = Space.com| quote = After mapping cosmic radiation levels at various depths on Mars, researchers have concluded that any life within the first several yards of the planet's surface would be killed by lethal doses of cosmic radiation.}}</ref><ref name='Dartnell'>{{cite journal |doi=10.1029/2006GL027494 |quote=Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack-ice requires a drill depth of at least 7.5 m. |title=Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology |year=2007 |last1=Dartnell |first1=L. R. |last2=Desorgher |first2=L. |last3=Ward |first3=J. M. |last4=Coates |first4=A. J. |journal=Geophysical Research Letters |volume=34 |issue=2 |pages=L02207}}</ref><ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 |quote=That's because any bacteria that may once have lived on the surface have long since been exterminated by cosmic radiation sleeting through the thin Martian atmosphere.}}</ref> The team calculated that the cumulative damage to [[DNA]] and [[RNA]] by cosmic radiation would limit retrieving viable dormant cells on Mars to depths greater than 7.5 metres below the planet's surface.<ref name="Dartnell" />

Even the most radiation-tolerant Earthly bacteria would survive in dormant [[spore]] state only 18,000 years at the surface; at 2 meters —the greatest depth at which the [[ExoMars]] rover will be capable of reaching— survival time would be 90,000 to half million years, depending on the type of rock.<ref name='DartnellGeographic'>{{cite web | author = Richard A. Lovet | title = Mars Life May Be Too Deep to Find, Experts Conclude| url = http://news.nationalgeographic.co.uk/news/2007/02/070202-mars-life.html | work = National Geographic News |date= February 2, 2007 }}</ref>

The [[Radiation assessment detector]] on board the [[Curiosity (rover)|''Curiosity'' rover]] is currently quantifying the flux of biologically hazardous radiation at the surface of Mars today, and will help determine how these fluxes vary on diurnal, seasonal, solar cycle and episodic (flare, storm) timescales. These measurements will allow calculations of the depth in rock or soil to which this flux, when integrated over long timescales, provides a lethal dose for known terrestrial organisms. Through such measurements, scientists can learn how deep below the surface life would have to be, or have been in the past, to be protected.<ref>{{cite journal |bibcode=2013EGUGA..1512596H |title=The Radiation Environment on the Martian Surface and during MSL's Cruise to Mars |last1=Hassler |first1=Donald M. |last2=Zeitlin |first2=Cary |last3=Wimmer-Schweingruber |first3=Robert F. |last4=Ehresmann |first4=Bent |last5=Rafkin |first5=Scot |last6=Martin |first6=Cesar |last7=Boettcher |first7=Stephan |last8=Koehler |first8=Jan |last9=Guo |first9=Jingnan |volume=15 |year=2013 |pages=12596 |journal=EGU General Assembly 2013}}</ref>

===Nitrogen fixation===
After carbon, [[nitrogen]] is arguably the most important element needed for life. Thus, measurements of [[nitrate]] over the range of 0.1% to 5% are required to address the question of its occurrence and distribution. There is nitrogen (as N2) in the atmosphere at low levels, but this is not adequate to support [[nitrogen fixation]] for biological incorporation.<ref name='Icebreaker2018'>{{cite journal | title = The ''Icebreaker Life'' Mission to Mars: A Search for Biomolecular Evidence for Life | journal = Astrobiology | date = April 5, 2013 | first = Christopher P. McKay | coauthors = Carol R. Stoker, Brian J. Glass, Arwen I. Davé, Alfonso F. Davila, Jennifer L. Heldmann, Margarita M. Marinova, Alberto G. Fairen, Richard C. Quinn, Kris A. Zacny, Gale Paulsen, Peter H. Smith, Victor Parro, Dale T. Andersen, Michael H. Hecht, Denis Lacelle, and Wayne H. Pollard. | volume = 13 | issue = 4 | pages = 334–353 | doi = 10.1089/ast.2012.0878 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2012.0878 | accessdate = 2013-06-30}}</ref> Nitrogen in the form of [[nitrate]], if present, could be a resource for human exploration both as a nutrient for plant growth and for use in chemical processes. On Earth, nitrates correlate with perchlorates in desert environments, and this may also be true on Mars. Nitrate is expected to be stable on Mars and to have formed in shock and electrical processes. Currently there is no data on its availability.<ref name='Icebreaker2018'/>

===Low pressure===
Further complicating estimates of the habitability of the Martian surface is the fact that very little is known on the growth of microorganisms at pressures close to the conditions found on the surface of Mars. Some teams determined that some bacteria may be capable of cellular replication down to 25 mbar, but that is still above the atmospheric pressures found on Mars (range 1–14 mbar).<ref name=Serratia>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref> In another study, twenty-six strains of bacteria were chosen based on their recovery from spacecraft assembly facilities, and only ''[[Serratia liquefaciens]]'' strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.<ref name=Serratia/>

==Liquid water==

{{Main|Water on Mars}}
[[File:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of past water coverage on Mars.]]
Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours.<ref>{{cite journal |bibcode=2005JGRE..11005004H |doi=10.1029/2004JE002261 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |year=2005 |last1=Heldmann |first1=Jennifer L. |first2=Owen B. |last2=Toon |first3=Wayne H. |last3=Pollard |first4=Michael T. |last4=Mellon |first5=John |last5=Pitlick |first6=Christopher P. |last6=McKay |first7=Dale T. |last7=Andersen |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004}}</ref><ref>{{cite journal |bibcode=2006GeoRL..3311201K |title=Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement |last1=Kostama |first1=V.-P. |last2=Kreslavsky |first2=M. A. |last3=Head |first3=J. W. |volume=33 |year=2006 |pages=11201 |journal=Geophysical Research Letters |doi=10.1029/2006GL025946 |issue=11}}</ref> Liquid water does not appear at the surface itself,<ref>{{cite journal |bibcode=2006IJMSE...2...83H |title=Transient liquid water near an artificial heat source on Mars |last1=Hecht |first1=Michael H. |last2=Vasavada |first2=Ashwin R. |volume=2 |year=2006 |pages=83 |journal=International Journal of Mars Science and Exploration |doi=10.1555/mars.2006.0006}}</ref> but it could form in minuscule amounts around dust particles in snow heated by the Sun.<ref name=Shiga2009>{{cite web |first=David |last=Shiga |url=http://www.newscientist.com/article/mg20427373.700 |date=December 7, 2009 |title=Watery niche may foster life on Mars |work=New Scientist}}</ref><ref name=Shiga2009/><ref name="news.softpedia">{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}{{verify credibility|date=June 2013}}</ref><ref name="news.softpedia" /> Also, the ancient equatorial ice sheets beneath the ground may slowly sublimate or melt, accessible from the surface via caves.<ref>Michael T. Mellon [http://science.nasa.gov/media/medialibrary/2011/06/29/Mellon_Water_PPS_May2011_-_TAGGED.pdf Subsurface Ice at Mars: A review of ice and water in the equatorial regions] University of Colorado 10 May 2011 Planetary Protection Subcommittee Meeting</ref><ref>Robert Roy Britt [http://www.space.com/812-ice-packs-methane-mars-suggest-present-life.html Ice Packs and Methane on Mars Suggest Present Life Possible] space.com 22 February 2005</ref><ref>{{cite journal |bibcode=1997JGR...10219357M |title=The persistence of equatorial ground ice on Mars |last1=Mellon |first1=Michael T. |last2=Jakosky |first2=Bruce M. |last3=Postawko |first3=Susan E. |volume=102 |year=1997 |pages=19357–69 |journal=Journal of Geophysical Research |doi=10.1029/97JE01346}}</ref><ref>{{cite journal |bibcode=2012LPICo1675.8001A |title=A Conceptual Model of Equatorial Ice Sheets on Mars |last1=Arfstrom |first1=J. D. |volume=1675 |year=2012 |pages=8001 |journal=Comparative Climatology of Terrestrial Planets}}</ref>

Water on Mars exists almost exclusively as water ice, located in the [[Martian polar ice caps]] and under the shallow Martian surface even at more temperate latitudes.<ref name="mars.jpl.nasa.gov">{{cite web| url=http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20020528a.html |title=Mars Odyssey: Newsroom |publisher=Mars.jpl.nasa.gov |date=May 28, 2002 |accessdate=December 19, 2010}}</ref><ref name="Feildman, T. 2004">{{cite journal |bibcode=2004JGRE..10909006F |doi=10.1029/2003JE002160 |title=Global distribution of near-surface hydrogen on Mars |year=2004 |last1=Feldman |first1=W. C. |journal=Journal of Geophysical Research |volume=109}}</ref> A small amount of water vapor is present in the [[Atmosphere of Mars|atmosphere]].<ref name="ucar">{{cite web| url=http://www.windows.ucar.edu/tour/link=/mars/exploring/MGS_water_clouds.html| title=Mars Global Surveyor Measures Water Clouds| accessdate=March 7, 2009}}</ref> There are no bodies of liquid water on the Martian surface because its atmospheric pressure at the surface averages {{Convert|600|Pa|sp=us}} —about 0.6% of Earth's mean sea level pressure— and because the temperature is far too low, ({{Convert|210|K|C}}) leading to immediate freezing. Despite this, about 3.8 billion years ago,<ref name=Baker>{{cite journal |bibcode=1991Natur.352..589B |title=Ancient oceans, ice sheets and the hydrological cycle on Mars |last1=Baker |first1=V. R. |last2=Strom |first2=R. G. |last3=Gulick |first3=V. C. |last4=Kargel |first4=J. S. |last5=Komatsu |first5=G. |volume=352 |year=1991 |pages=589 |journal=Nature |doi=10.1038/352589a0 |last6=Kale |first6=V. S. |issue=6336}}</ref> there was a denser [[atmosphere of Mars|atmosphere]], higher temperature, and vast amounts of liquid water flowed on the surface,<ref name=flashback>{{cite web| url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago |publisher=SPACE.com |date=June 22, 2000 |accessdate=December 19, 2010}}</ref><ref>{{cite web
| url=http://science.nasa.gov/headlines/y2001/ast05jan_1.htm
| title=Science@NASA, The Case of the Missing Mars Water
| accessdate=March 7, 2009}}</ref><ref name='Clay clues'>{{cite news | title = Mars Rover Opportunity Examines Clay Clues in Rock | date = May 17, 2013 | publisher = Jet Propulsion Laboratory | url = http://www.jpl.nasa.gov/news/news.php?release=2013-167 | work = NASA | accessdate = 2013-06-14}}</ref><ref>{{cite news | title = NASA Rover Helps Reveal Possible Secrets of Martian Life | date = November 29, 2005 | url = http://www.nasa.gov/home/hqnews/2005/nov/HQ_05415_rover_secrets_prt.htm | work = NASA | accessdate = 2013-06-20}}</ref> including large oceans.<ref>ISBN 0-312-24551-3{{page needed|date=June 2013}}{{full|date=June 2013}}</ref><ref name=Sea>{{cite web| url= http://www.psrd.hawaii.edu/July03/MartianSea.html |title=PSRD: Ancient Floodwaters and Seas on Mars |publisher=Psrd.hawaii.edu |date=July 16, 2003 |accessdate=December 19, 2010}}</ref><ref>{{cite web| url=http://www.spaceref.com/news/viewpr.html?pid=26947 |title=Gamma-Ray Evidence Suggests Ancient Mars Had Oceans |publisher=SpaceRef |date=November 17, 2008 |accessdate=December 19, 2010}}</ref><ref name="2003JGRE..108.5042C">{{cite journal |bibcode=2003JGRE..108.5042C |title=Oceans on Mars: An assessment of the observational evidence and possible fate |last1=Carr |first1=Michael H. |last2=Head |first2=James W. |volume=108 |year=2003 |pages=5042 |journal=Journal of Geophysical Research (Planets) |doi=10.1029/2002JE001963}}</ref><ref name="SFN-20130125">{{cite web |last=Harwood |first=William |title=Opportunity rover moves into 10th year of Mars operations |url=http://www.spaceflightnow.com/news/n1301/25opportunity/ |date=January 25, 2013 |publisher=Space Flight Now |accessdate=February 18, 2013 }}</ref> It has been estimated that the primordial oceans on Mars would have covered between 36% <ref name="ReferenceA">{{cite journal | last1 = Di Achille | first1 = Gaetano | last2 = Hynek | first2 = Brian M. | title = Ancient ocean on Mars supported by global distribution of deltas and valleys | journal=Nature Geoscience | volume = 3 | pages = 459–63 | year = 2010 | doi = 10.1038/ngeo891 |bibcode = 2010NatGe...3..459D | issue=7 |laysummary=http://www.sciencedaily.com/releases/2010/06/100613181245.htm |laysource=ScienceDaily |laydate=June 14, 2010}}</ref> and 75% of the planet.<ref name=Smith>{{cite journal |bibcode=1999Sci...286...94S |title=The gravity field of Mars: Results from Mars Global Surveyor |last1=Smith |first1=D. E. |last2=Sjogren |first2=W. L. |last3=Tyler |first3=G. L. |last4=Balmino |first4=G. |last5=Lemoine |first5=F. G. |last6=Konopliv |first6=A. S. |volume=286 |year=1999 |pages=94–7 |journal=Science |doi=10.1126/science.286.5437.94 |pmid=10506567 |issue=5437}}</ref>

[[File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in [[Newton (Martian crater)|Newton Crater]] ]]
Analysis of Martian sandstones, using data obtained from orbital spectrometry, suggests that the waters that previously existed on the surface of Mars would have had too high a salinity to support most Earth-like life. Tosca ''et al.'' found that the Martian water in the locations they studied all had [[water activity]], aw ≤ 0.78 to 0.86—a level fatal to most Terrestrial life.<ref>{{cite journal |bibcode=2008Sci...320.1204T |title=Water Activity and the Challenge for Life on Early Mars |last1=Tosca |first1=Nicholas J. |last2=Knoll |first2=Andrew H. |last3=McLennan |first3=Scott M. |volume=320 |year=2008 |pages=1204–7 |journal=Science |doi=10.1126/science.1155432 |pmid=18511686 |issue=5880}}</ref> [[Haloarchaea]], however, are able to live in hypersaline solutions, up to the saturation point.<ref>{{Cite journal |title=Extreme Halophiles Are Models for Astrobiology |journal=Microbe |year=2006 |first=Shiladitya |last=DasSarma |volume=1 |issue=3 |pages=120–6 |url=http://forms.asm.org/microbe/index.asp?bid=41227}}</ref>

In June 2000, possible evidence for current liquid water flowing at the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>{{cite journal |bibcode=2000Sci...288.2330M |title=Evidence for Recent Groundwater Seepage and Surface Runoff on Mars |last1=Malin |first1=Michael C. |last2=Edgett |first2=Kenneth S. |volume=288 |year=2000 |pages=2330–5 |journal=Science |doi=10.1126/science.288.5475.2330 |pmid=10875910 |issue=5475}}</ref><ref>{{cite conference |url=http://www.planets.ucla.edu/wp-content/form-data/mars-abstracts-2013/37-Martinez_2013_UCLA_Mars_Habitability.pdf |title=Present Day Liquid Water On Mars: Theoretical Expectations, Observational Evidence And Preferred Locations |first1=G. M. |last1=Martínez |first2=N. O. |last2=Renno |first3=H. M. |last3=Elliott |first4=E. |last4=Fischer |year=2013 |conference=The Present-day Mars Habitability Conference |location=Los Angeles}}</ref> Additional similar images were published in 2006, taken by the [[Mars Global Surveyor]], that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in steep crater walls and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago.

There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. Some suggest the flows were merely dry sand flows.<ref>{{cite journal | doi = 10.1016/j.icarus.2009.09.009 | last1 = Kolb | first1 = K. | last2 = Pelletier | year = 2010 | first2 = Jon D. | last3 = McEwen | first3 = Alfred S. | title = Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water | url = | journal=Icarus | volume = 205 | pages = 113–137 |bibcode = 2010Icar..205..113K }}</ref><ref name="ReferenceB">{{cite web| url=http://www.sciencedirect.com/science/journal/00191035 |title=Icarus | Vol 218, Iss 1, In Progress, (March, 2012) |publisher=ScienceDirect.com |date=2004-06-08 |accessdate=2012-01-16}}{{page needed|date=June 2013}}</ref><ref name=moon>[http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=12376 "University of Arizona Press Release"] March 16, 2006.</ref><ref>{{Cite journal| title=Mars Orbiter's Swan Song: The Red Planet Is A-Changin' |journal=Science |date=2006 - 12 - 8|first=Richard| last=Kerr| volume=314|issue=5805 |pages=1528–1529 |doi=10.1126/science.314.5805.1528| pmid=17158298}}</ref> Others suggest it may be liquid [[brine]] near the surface,<ref name=voanews>{{cite web| url= http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html| title=NASA Finds Possible Signs of Flowing Water on Mars| publisher=voanews.com| accessdate=August 5, 2011}}</ref><ref name=Ames>{{cite web|author=Source: Ames Research Center Posted Saturday, June 6, 2009 |url=http://www.spaceref.com/news/viewpr.html?pid=28377 |title=NASA Scientists Find Evidence for Liquid Water on a Frozen Early Mars |publisher=SpaceRef |date=June 6, 2009 |accessdate=December 19, 2010}}</ref><ref>{{cite web|url=http://www.space.com/scienceastronomy/mars-phoenix-water-salt-data-100831.html |title=Dead Spacecraft on Mars Lives on in New Study |publisher=SPACE.com |date=June 10, 2008 |accessdate=December 19, 2010}}</ref> but the exact source of the water and the mechanism behind its motion are not understood.<ref name=hirise>{{cite journal |bibcode=2011Sci...333..740M |title=Seasonal Flows on Warm Martian Slopes |last1=McEwen |first1=Alfred S. |last2=Ojha |first2=Lujendra |last3=Dundas |first3=Colin M. |last4=Mattson |first4=Sarah S. |last5=Byrne |first5=Shane |last6=Wray |first6=James J. |last7=Cull |first7=Selby C. |last8=Murchie |first8=Scott L. |last9=Thomas |first9=Nicolas |volume=333 |year=2011 |pages=740–3 |journal=Science |doi=10.1126/science.1204816 |pmid=21817049 |issue=6043}}</ref>

===Silica===
[[File:Spirit Mars Silica April 20 2007.jpg|thumb|The silica-rich patch discovered by [[Spirit (rover)|Spirit rover]] ]]
In May 2007, the [[Spirit rover]] disturbed a patch of ground with its inoperative wheel, uncovering an area extremely rich in [[silica]] (90%).<ref>{{cite press release |title=Mars Rover Spirit Unearths Surprise Evidence of Wetter Past |date=May 21, 2007 |publisher=[[Jet Propulsion Laboratory]] |url=http://www.nasa.gov/mission_pages/mer/mer-20070521.html |accessdate=June 27, 2013}}</ref> The feature is reminiscent of the effect of [[hot spring]] water or steam coming into contact with volcanic rocks. Scientists consider this as evidence of a past environment that may have been favorable for microbial life, and theorize that one possible origin for the silica may have been produced by the interaction of soil with acid vapors produced by volcanic activity in the presence of water.<ref Name="20071210a">{{cite press release |title=Mars Rover Investigates Signs of Steamy Martian Past |publisher=[[Jet Propulsion Laboratory]] |date=December 10, 2007 |url=http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html |accessdate=June 27, 2013}}</ref>

Based on Earth analogs, [[Hydrothermal vent|hydrothermal systems]] on Mars would be highly attractive for their potential for preserving [[Organic compound|organic]] and [[Inorganic compound|inorganic]] [[biosignature]]s.<ref name='Leveille'>{{cite journal |bibcode=2010AGUFM.P12A..07L |title=Mineralized iron oxidizing bacteria from hydrothermal vents: Targeting biosignatures on Mars |last1=Leveille |first1=R. J. |volume=12 |year=2010 |pages=07 |journal=American Geophysical Union}}</ref><ref>{{cite journal |bibcode=1993Icar..101..129W |title=Preservation of Biological Information in Thermal Spring Deposits: Developing a Strategy for the Search for Fossil Life on Mars |last1=Walter |first1=M. R. |last2=Des Marais |first2=David J. |volume=101 |year=1993 |pages=129–43 |journal=Icarus |doi=10.1006/icar.1993.1011 |pmid=11536937 |issue=1}}</ref><ref>{{cite journal |bibcode=2000Icar..147...49A |title=Microscopic Physical Biomarkers in Carbonate Hot Springs: Implications in the Search for Life on Mars |last1=Allen |first1=Carlton C. |last2=Albert |first2=Fred G. |last3=Chafetz |first3=Henry S. |last4=Combie |first4=Joan |last5=Graham |first5=Catherine R. |last6=Kieft |first6=Thomas L. |last7=Kivett |first7=Steven J. |last8=McKay |first8=David S. |last9=Steele |first9=Andrew |volume=147 |year=2000 |pages=49–67 |journal=Icarus |doi=10.1006/icar.2000.6435 |pmid=11543582 |issue=1}}</ref> For this reason, hydrothermal deposits are regarded as important targets in the exploration for fossil evidence of ancient Martian life.<ref>{{cite journal |bibcode=1999JGR...104.8489W |title=A Mössbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration |last1=Wade |first1=Manson L. |last2=Agresti |first2=David G. |last3=Wdowiak |first3=Thomas J. |last4=Armendarez |first4=Lawrence P. |last5=Farmer |first5=Jack D. |volume=104 |year=1999 |pages=8489–507 |journal=Journal of Geophysical Research |doi=10.1029/1998JE900049 |pmid=11542933 |issue=E4}}</ref><ref>{{cite journal |bibcode=1995LPI....26....7A |title=A Mossbauer Investigation of Hot Springs Iron Deposits |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |last5=Farmer |first5=J. D. |volume=26 |year=1995 |pages=7 |journal=Abstracts of the Lunar and Planetary Science Conference}}</ref><ref>{{cite journal |bibcode=1997LPICo.916....1A |title=Mössbauer Spectroscopy of Thermal Springs Iron Deposits as Martian Analogs |last1=Agresti |first1=D. G. |last2=Wdowiak |first2=T. J. |last3=Wade |first3=M. L. |last4=Armendarez |first4=L. P. |volume=916 |year=1997 |pages=1 |journal=Early Mars: Geologic and Hydrologic Evolution}}</ref>

==Possible biosignatures==

===Methane===
{{Main|Atmosphere of Mars#Methane}}
Trace amounts of [[methane]] in the atmosphere of Mars were discovered in 2003 and verified in 2004.<ref>{{cite journal |bibcode=2003DPS....35.1418M |title=A Sensitive Search for Methane on Mars |last1=Mumma |first1=M. J. |last2=Novak |first2=R. E. |last3=Disanti |first3=M. A. |last4=Bonev |first4=B. P. |volume=35 |year=2003 |pages=937 |journal=American Astronomical Society}}</ref><ref>{{cite journal |bibcode=2009Sci...323.1041M |title=Strong Release of Methane on Mars in Northern Summer 2003 |last1=Mumma |first1=Michael J. |last2=Villanueva |first2=Geronimo L. |last3=Novak |first3=Robert E. |last4=Hewagama |first4=Tilak |last5=Bonev |first5=Boncho P. |last6=Disanti |first6=Michael A. |last7=Mandell |first7=Avi M. |last8=Smith |first8=Michael D. |volume=323 |year=2009 |pages=1041–5 |journal=Science |doi=10.1126/science.1165243 |pmid=19150811 |issue=5917}}</ref><ref>{{cite journal |bibcode=2004Sci...306.1758F |title=Detection of Methane in the Atmosphere of Mars |last1=Formisano |first1=Vittorio |last2=Atreya |first2=Sushil |last3=Encrenaz |first3=Thérèse |last4=Ignatiev |first4=Nikolai |last5=Giuranna |first5=Marco |volume=306 |year=2004 |pages=1758–61 |journal=Science |doi=10.1126/science.1101732 |pmid=15514118 |issue=5702}}</ref><ref>{{cite journal |bibcode=2004Icar..172..537K |title=Detection of methane in the martian atmosphere: Evidence for life? |last1=Krasnopolsky |first1=Vladimir A. |last2=Maillard |first2=Jean Pierre |last3=Owen |first3=Tobias C. |volume=172 |year=2004 |pages=537–47 |journal=Icarus |doi=10.1016/j.icarus.2004.07.004 |issue=2}}</ref><ref>{{cite press release |title=Mars Express confirms methane in the Martian atmosphere |publisher=[[ESA]] |url=http://www.esa.int/SPECIALS/Mars_Express/SEMZ0B57ESD_0.html |accessdate=March 17, 2006 |date=March 30, 2004}}</ref><ref>{{cite journal |bibcode=2005Icar..178..277M |title=Desert methane: Implications for life detection on Mars |last1=Moran |first1=Mark |last2=Miller |first2=Joseph D. |last3=Kral |first3=Tim |last4=Scott |first4=Dave |volume=178 |year=2005 |pages=277–80 |journal=Icarus |doi=10.1016/j.icarus.2005.06.008}}</ref> As methane is an unstable gas, its presence indicates that there must be an active source on the planet in order to keep such levels in the atmosphere. It is estimated that Mars must produce 270 ton/year of methane,<ref>{{cite journal |bibcode=2006Icar..180..359K |title=Some problems related to the origin of methane on Mars |last1=Krasnopolsky |first1=Vladimir A. |volume=180 |year=2006 |pages=359–67 |journal=Icarus |doi=10.1016/j.icarus.2005.10.015 |issue=2}}</ref><ref>[http://www.pfs-results.it/ Planetary Fourier Spectrometer website] (ESA, Mars Express){{vs|needs a more specific reference|date=June 2013}}</ref> but [[asteroid]] impacts account for only 0.8% of the total methane production. Although geologic sources of methane such as [[serpentinization]] are possible, the lack of current [[volcanism]], [[hydrothermal activity]] or [[Hotspot (geology)|hotspots]] are not favorable for geologic methane. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,<ref>{{cite journal |doi=10.1016/j.epsl.2009.09.041 |bibcode=2009E&PSL.288..382C |laysummary=http://www.physorg.com/news179499648.html |laysource=Phys.org |laydate=December 8, 2009 |title=Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars |year=2009 |last1=Court |first1=Richard W. |last2=Sephton |first2=Mark A. |journal=Earth and Planetary Science Letters |volume=288 |issue=3–4 |pages=382–5}}</ref> research published in 2012 suggest that a source may be [[organic compound]]s on meteorites that are converted to methane by [[ultraviolet]] radiation.<ref>{{cite journal |bibcode=2012Natur.486...93K |title=Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere |last1=Keppler |first1=Frank |last2=Vigano |first2=Ivan |last3=McLeod |first3=Andy |last4=Ott |first4=Ulrich |last5=Früchtl |first5=Marion |last6=Röckmann |first6=Thomas |volume=486 |year=2012 |pages=93–6 |journal=Nature |doi=10.1038/nature11203 |pmid=22678286 |issue=7401}}</ref>
[[File:Martian Methane Map.jpg|thumb|left|300px|right|Distribution of [[methane]] in the atmosphere of Mars in the Northern Hemisphere during summer]]
The existence of life in the form of [[microorganism]]s such as [[methanogen]]s is among possible, but as yet unproven sources. If microscopic Martian life is producing the methane, it likely resides far below the surface, where it is still warm enough for liquid water to exist.<ref name=Steigerwald>{{Cite news| first=Bill| last=Steigerwald| title=Martian Methane Reveals the Red Planet is not a Dead Planet| date=January 15, 2009 |publisher=NASA |url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html |work=NASA's Goddard Space Flight Center| pages=| accessdate=June 6 24, 2013| quote= If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist}}</ref>

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and ''in vitro'' experiments testing growth of [[methanogen|methanogenic bacteria]] on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0wt% [[perchlorate]] salt.<ref name=Kral >{{cite journal |bibcode=2009M&PSA..72.5136K |title=Can Methanogens Grow in a Perchlorate Environment on Mars? |last1=Kral |first1=T. A. |last2=Goodhart |first2=T. |last3=Howe |first3=K. L. |last4=Gavin |first4=P. |volume=72 |year=2009 |pages=5136 |journal=72nd Annual Meeting of the Meteoritical Society}}</ref> The results reported indicate that the perchlorates discovered by the [[Phoenix Lander]] would not rule out the possible presence of methanogens on Mars.<ref name=Kral /><ref name=Howe >{{cite journal |bibcode=2009LPI....40.1287H |title=Methane Production by Methanogens in Perchlorate-supplemented Media |last1=Howe |first1=K. L. |last2=Gavin |first2=P. |last3=Goodhart |first3=T. |last4=Kral |first4=T. A. |volume=40 |year=2009 |pages=1287 |journal=40th Lunar and Planetary Science Conference}}</ref>

A team led by Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.<ref name=Howe /><ref name='Levin 2009'>{{cite book |bibcode=2009SPIE.7441E..12L |chapter=Methane and life on Mars |last1=Levin |first1=Gilbert V. |last2=Straat |first2=Patricia Ann |volume=7441 |year=2009 |pages=12–27 |title=Instruments and Methods for Astrobiology and Planetary Missions XII |doi=10.1117/12.829183 |editor1-last=Hoover |editor1-first=Richard B |editor2-last=Levin |editor2-first=Gilbert V |editor3-last=Rozanov |editor3-first=Alexei Y |editor4-last=Retherford |editor4-first=Kurt D |isbn=978-0-8194-7731-6}}</ref>

In June 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of life on Mars.<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |bibcode=2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web |author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet τ Boötis b |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |arxiv=1206.6109 |bibcode=2012Natur.486..502B |issue=7404 }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref>

The [[Curiosity rover]], which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;<ref>{{Cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |title=Making Sense of Mars Methane |accessdate=October 8, 2008 |last=Tenenbaum |first=David |date=June 9, 2008 |work=Astrobiology Magazine|archiveurl= http://web.archive.org/web/20080923195833/http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2765&mode=thread&order=0&thold=0 |archivedate= 23 September 2008 | deadurl= no}}</ref> but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.<ref>{{Cite news|first=Bill|last=Steigerwald|coauthors=|authorlink=|title=Martian Methane Reveals the Red Planet is not a Dead Planet|date=January 15, 2009|publisher=NASA|url=http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|work=NASA's Goddard Space Flight Center|pages=| accessdate=January 24, 2009|language=| archiveurl=http://web.archive.org/web/20090117141425/http://www.nasa.gov/mission_pages/mars/news/marsmethane.html|archivedate= 17 January 2009 | deadurl= no}}</ref> The first measurements with the [[Sample Analysis at Mars|Tunable Laser Spectrometer (TLS)]] indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.<ref>{{cite web |url=http://www.ustream.tv/nasajpl |title=Mars Curiosity Rover News Telecon -November 2, 2012}}</ref><ref name="Science-20121102">{{cite web |last=Kerr |first=Richard A. |title=Curiosity Finds Methane on Mars, or Not|url=http://news.sciencemag.org/sciencenow/2012/11/curiosity-finds-methane-on-mars-.html |date=November 2, 2012|publisher=[[Science (journal)]] |accessdate=November 3, 2012 }}</ref><ref name="Space-20121102">{{cite web|last=Wall |first=Mike |title=Curiosity Rover Finds No Methane on Mars — Yet|url=http://www.space.com/18333-mars-rover-curiosity-methane-measurements.html |date=November 2, 2012|publisher=[[Space.com]] |accessdate=November 3, 2012 }}</ref><ref name="NYT-20121102">{{cite news |last=Chang|first=Kenneth |title=Hope of Methane on Mars Fades|url=http://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |publisher=[[New York Times]] |accessdate=November 3, 2012 }}</ref> The [[Mars Trace Gas Mission]] orbiter planned to launch in 2016 would further study the methane,<ref>{{Cite news |first=Paul |last=Rincon |title=Agencies outline Mars initiative |date=July 9, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |publisher=BBC News |accessdate=July 26, 2009}}</ref><ref>{{Cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=March 6, 2009 |agency=[[Asian News International]] |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |publisher=Thaindian News |accessdate=July 26, 2009}}</ref> as well as its decomposition products such as [[formaldehyde]] and [[methanol]].

===Formaldehyde===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] had detected traces of [[formaldehyde]] in the [[atmosphere of Mars]]. Vittorio Formisano, the director of the PFS, has speculated that the formaldehyde could be the byproduct of the oxidation of methane and, according to him, would provide evidence that Mars is either extremely geologically active or harbouring colonies of microbial life.<ref>{{cite journal |doi=10.1038/news050221-15 |first=Mark |last=Peplow |title=Formaldehyde claim inflames martian debate |journal=Nature |date=February 25, 2005}}</ref><ref>{{Cite news|first=Jenny|last=Hogan|coauthors=|title=A whiff of life on the Red Planet|date=February 16, 2005|publisher=New Scientist magazine|url=http://www.newscientist.com/article.ns?id=dn7014|work=|pages=|accessdate=August 18, 2008|language=}}</ref> NASA scientists consider the preliminary findings well worth a follow-up, but have also rejected the claims of life.<ref name=PFS>{{cite journal |doi=10.1038/news050905-10 |title=Martian methane probe in trouble |date=September 7, 2005 |last1=Peplow |first1=Mark |journal=Nature}}</ref><ref name='NASA Releasease : 05-052'>{{Cite news|first=|last=|coauthors=|title=NASA Statement on False Claim of Evidence of Life on Mars|date=February 18, 2005|publisher=NASA|url=http://www1.nasa.gov/home/hqnews/2005/feb/HQ_05052_mars_claim.html|work=NASA News|pages=|accessdate=August 18, 2008|language=}}</ref>

===Meteorites===
[[NASA]] maintains a catalog of 34 [[Mars meteorite]]s.<ref>{{Cite web|url=http://www2.jpl.nasa.gov/snc/index.html|title=Mars Meteorites|accessdate=February 16, 2010|publisher=NASA}}</ref> These assets are highly valuable since they are the only physical samples available of Mars. Studies conducted by NASA's [[Johnson Space Center]] show that at least three of the meteorites contain potential evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called [[Organism|biomorphs]]). Although the scientific evidence collected is reliable, its interpretation varies. To date, none of the original lines of scientific evidence for the hypothesis that the biomorphs are of [[exobiological]] origin (the so-called biogenic hypothesis) have been either discredited or positively ascribed to non-biological explanations.<ref name="meteoritos-Bio">[http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf Evidence for ancient Martian life]. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.</ref>

Over the past few decades, seven criteria have been established for the recognition of past life within terrestrial geologic samples. Those criteria are:<ref name="meteoritos-Bio"/>
#Is the geologic context of the sample compatible with past life?
#Is the age of the sample and its stratigraphic location compatible with possible life?
#Does the sample contain evidence of cellular morphology and colonies?
#Is there any evidence of biominerals showing chemical or mineral disequilibria?
#Is there any evidence of stable isotope patterns unique to biology?
#Are there any organic biomarkers present?
#Are the features indigenous to the sample?

For general acceptance of past life in a geologic sample, essentially most or all of these criteria must be met. All seven criteria have not yet been met for any of the Martian samples, but continued investigations are in progress.<ref name="meteoritos-Bio"/>

As of 2010, reexaminations of the biomorphs found in the three Martian meteorites are underway with more advanced analytical instruments than previously available.

==== ALH84001 ====
[[File:ALH84001 structures.jpg|right|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
The [[ALH84001]] meteorite was found in December 1984 in [[Antarctica]], by members of the [[ANSMET]] project; the meteorite weighs {{Convert|1.93|kg}}.<ref>{{Cite web|url=http://www.lpi.usra.edu/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604|title=Allan Hills 84001|accessdate=August 21, 2008|month=April|year=2008|publisher=The Meteorolitical Society}}</ref> The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of [[magnetite]] that on Earth, is only found in association with certain microorganisms.<ref name="meteoritos-Bio"/> Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the [[magnetite]] in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected. The meteorite displays indication of relatively low temperature secondary mineralization by water and shows evidence of preterrestrial aqueous alteration.{{Clarify|date=February 2013}} Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface.

Some structures resembling the mineralized casts of terrestrial bacteria and their appendages (fibrils) or by-products (extracellular polymeric substances) occur in the rims of carbonate globules and preterrestrial aqueous alteration regions.<ref name=disbelief>{{Cite web|title=After 10 years, few believe life on Mars|url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html|last=Crenson|first=Matt|publisher=[[Associated Press]] (on [http://www.space.com space.com])|date=August 6, 2006|accessdate=August 6, 2006}}{{dead link|date=June 2013}}</ref><ref>{{cite journal |bibcode=1996Sci...273..924M |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |last1=McKay |first1=David S. |last2=Gibson |first2=Everett K. |last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |volume=273 |year=1996 |pages=924–30 |journal=Science |doi=10.1126/science.273.5277.924 |pmid=8688069 |issue=5277}}</ref> The size and shape of the objects is consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.

In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the [[magnetite]]s in the meteorite.<ref>{{cite news | first = William P. Jeffs | title = New Study Adds to Finding of Ancient Life Signs in Mars Meteorite | date = 30 November 2009 | publisher = NASA News | url = http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html | work = NASA | accessdate = 2013-06-04}}</ref><ref>{{cite journal |bibcode=2009GeCoA..73.6631T |title=Origins of magnetite nanocrystals in Martian meteorite ALH84001 |last1=Thomas-Keprta |first1=K. L. |last2=Clemett |first2=S. J. |last3=McKay |first3=D. S. |last4=Gibson |first4=E. K. |last5=Wentworth |first5=S. J. |volume=73 |year=2009 |pages=6631–77 |journal=Geochimica et Cosmochimica Acta |doi=10.1016/j.gca.2009.05.064 |issue=21}}</ref>
[[File:Nakhla meteorite.jpg|thumb|left|Nakhla meteorite]]

====Nakhla====
The [[Nakhla meteorite]] fell on Earth on June 28, 1911 on the locality of Nakhla, [[Alexandria]], [[Egypt]].<ref name="NASA">{{Cite web|url=http://www2.jpl.nasa.gov/snc/nakhla.html|title=The Nakhla Meteorite|accessdate=August 17, 2008|last=Baalke|first=Ron|year=1995|work=Jet Propulsion Lab|publisher=NASA}}</ref><ref>{{Cite web|url=http://www.nhm.ac.uk/nature-online/virtual-wonders/vrmeteorite5.html|title=Rotating image of a Nakhla meteorite fragment|accessdate=August 17, 2008|year=2008|publisher=London Natural History Museum}}</ref>

In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects<ref>{{Cite news|first=Paul|last=Rincon|coauthors=|title=Space rock re-opens Mars debate|date=February 8, 2006|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/4688938.stm|work=BBC News|pages=|accessdate=August 17, 2008|language=}}</ref> of the size and shape consistent with Earthly [[fossil]]ized [[nanobacteria]], but the existence of nanobacteria itself is controversial.
Analysis with [[gas chromatography]] and [[mass spectrometry]] (GC-MS) studied its high molecular weight [[polycyclic aromatic hydrocarbons]] in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".<ref name="meteoritos-Bio"/><ref>{{Cite web|url=http://www-curator.jsc.nasa.gov/antmet/mmc/Nakhla.pdf|title=Mars Meteorite Compendium|accessdate=August 21, 2008|last=Meyer|first=C.|year=2004|format=PDF|publisher=NASA}}</ref>

This caused additional interest in this meteorite, so in 2006, NASA managed to obtain an additional and larger sample from the London Natural History Museum. On this second sample, a large dendritic [[carbon]] content was observed. When the results and evidence were published on 2006, some independent researchers claimed that the carbon deposits are of biologic origin. However, it was remarked that since carbon is the fourth most abundant element in the [[Universe]], finding it in curious patterns is not indicative or suggestive of biological origin.<ref>{{Cite news|first=David|last=Whitehouse|coauthors=|title=Life on Mars - new claims|date=August 27, 1999|publisher=|url=http://news.bbc.co.uk/2/hi/science/nature/289214.stm|work=BBC News|pages=|accessdate=August 20, 2008|language=}}</ref><ref>Compilation of scientific research references on the Nakhla meteorite: http://curator.jsc.nasa.gov/antmet/marsmets/nakhla/references.cfm</ref>

====Shergotty====
The [[Shergotty meteorite]], a 4 kg Martian meteorite, fell on Earth on [[Sherghati|Shergotty]], [[India]] on August 25, 1865 and was retrieved by witnesses almost immediately.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergoti Meteorite - JPL, NASA]</ref> This meteorite is relatively young, calculated to have been formed on Mars only 165 million years ago from volcanic origin. It is composed mostly of [[pyroxene]] and thought to have undergone preterrestrial aqueous alteration for several centuries. Certain features in its interior suggest remnants of a biofilm and its associated microbial communities.<ref name="meteoritos-Bio"/> Work is in progress on searching for [[magnetite]]s within alteration phases.

==Geysers on Mars==
{{Double image|right|Geysers on Mars.jpg|{{#expr: (200 * (516 / 726)) round 0}}|Mars Global Surveyor 1.jpg|{{#expr: (200 * (321 / 537)) round 0}}|Artist concept showing sand-laden jets erupt from geysers on Mars. | Close up of dark dune spots, likely created by cold geyser-like eruptions.}}
{{Main|Geysers on Mars}}

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 – and probably water –increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.<ref name=2006-100 >{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Findings Suggest Jets Bursting From Martian Ice Cap|date=August 16, 2006|publisher=NASA|url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100|work=Jet Propulsion Laboratory|pages=|accessdate=August 11, 2009|language=}}</ref><ref name=Kieffer2000 >{{cite journal |bibcode=2000mpse.conf...93K |title=Annual Punctuated CO2 Slab-Ice and Jets on Mars |last1=Kieffer |first1=H. H. |year=2000 |pages=93 |journal=International Conference on Mars Polar Science and Exploration}}</ref><ref name=Portyankina >{{cite journal |bibcode=2006LPICo1323.8040P |title=Simulations of Geyser-type Eruptions in Cryptic Region of Martian South Polar Cap |last1=Portyankina |first1=G. |last2=Markiewicz |first2=W. J. |last3=Garcia-Comas |first3=M. |last4=Keller |first4=H. U. |last5=Bibring |first5=J.-P. |last6=Neukum |first6=G. |volume=1323 |year=2006 |pages=8040 |journal=Fourth International Conference on Mars Polar Science and Exploration}}</ref><ref name=Hugh2006 >{{cite journal |bibcode=2006Natur.442..793K |title=CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap |last1=Kieffer |first1=Hugh H. |last2=Christensen |first2=Philip R. |last3=Titus |first3=Timothy N. |volume=442 |year=2006 |pages=793–6 |journal=Nature |doi=10.1038/nature04945 |pmid=16915284 |issue=7104}}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars.

A team of Hungarian scientists proposes that the geysers' most visible features, dark dune spots and spider channels, may be colonies of [[photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesize and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When the layer has completely melted, the microorganisms rapidly desiccate and turn black, surrounded by a grey aureole.<ref name=Andras >{{cite journal |bibcode=2001LPI....32.1543H |title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Gesztesi |first3=A. |last4=Bérczi |first4=Sz. |last5=Szathmáry |first5=E. |volume=32 |year=2001 |pages=1543 |journal=32nd Annual Lunar and Planetary Science Conference}}</ref><ref name="Pócs et al 2004">{{cite journal |bibcode=2004eab..conf..265P |title=Possible crypto-biotic-crust on Mars? |last1=Pócs |first1=T. |last2=Horváth |first2=A. |last3=Gánti |first3=T. |last4=Bérczi |first4=Sz. |last5=Szathemáry |first5=E. |volume=545 |year=2004 |pages=265–6 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology}}</ref><ref name="Pócs et al 2004" /><ref>{{cite journal |doi=10.1023/A:1025705828948 |year=2003 |last1=Gánti |first1=Tibor |last2=Horváth |first2=András |last3=Bérczi |first3=Szaniszló |last4=Gesztesi |first4=Albert |last5=Szathmáry |first5=Eörs |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=4/5 |pages=515–57 |title=Dark Dune Spots: Possible Biomarkers on Mars?}}</ref> The Hungarian scientists believe that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{cite journal |bibcode=2002LPI....33.1108H |title=Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation |last1=Horváth |first1=A. |last2=Gánti |first2=T. |last3=Bérczi |first3=Sz. |last4=Gesztesi |first4=A. |last5=Szathmáry |first5=E. |volume=33 |year=2002 |pages=1108 |journal=33rd Annual Lunar and Planetary Science Conference}}</ref><ref>{{Cite web|url=http://www.monochrom.at/dark-dune-spots/|title=Dark Dune Spots - Could it be that it's alive?|accessdate=September 4, 2009|last=András Sik|first=Ákos Kereszturi|publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme >{{cite journal |title=Martian Spiders |journal=Marsbugs |date=June 9, 2003 |first1=Greg M. |last1=Orme |first2=Peter K. |last2=Ness |volume=10 |issue=23 |pages=5–7 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=September 6, 2009 |archiveurl=http://web.archive.org/web/20070927032609/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=September 27, 2007}}</ref>

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, they might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from solar radiation.<ref name=Manrubia >{{cite journal |bibcode=2004eab..conf...77M |title=Comparative analysis of geological features and seasonal processes in 'Inca City' and 'Pityusa Patera' regions on Mars |last1=Manrubia |first1=S. C. |last2=Prieto Ballesteros |first2=O. |last3=González Kessler |first3=C. |last4=Fernández Remolar |first4=D. |last5=Córdoba-Jabonero |first5=C. |last6=Selsis |first6=F. |last7=Bérczi |first7=S. |last8=Gánti |first8=T. |last9=Horváth |first9=A. |volume=545 |year=2004 |pages=77–80 |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |isbn=92-9092-856-5}}</ref> A British team also considers the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[geothermal]] energy source.<ref name=Ness >{{cite journal |bibcode=2002JBIS...55...85N |title=Spider-Ravine Models and Plant-Like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin |last1=Ness |first1=Peter K. |first2=Greg M. |last2=Orme |volume=55 |issue=3/4 |year=2002 |pages=85–108 |journal=Journal of the British Interplanetary Society}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> It has been proposed to develop the [[Mars Geyser Hopper]] lander to study the geysers up close.<ref>{{cite conference |first1=Geoffrey |last1=Landis |first2=Steven |last2=Oleson |first3=Melissa |last3=McGuire |year=2012 |title=Design Study for a Mars Geyser Hopper |conference=50th AIAA Aerospace Sciences Meeting |location=Nashville |url=http://ntrs.nasa.gov/search.jsp?R=20120004036 |doi=10.2514/6.2012-631 |doi_brokendate=June 27, 2013}}</ref>

==Forward contamination==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref>{{cite book |author1=Committee on an Astrobiology Strategy for the Exploration of Mars |author2=National Research Council |year=2007 |chapter=Planetary Protection for Mars Missions |chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 |pages=95–8 |title=An Astrobiology Strategy for the Exploration of Mars |publisher=The National Academies Press |isbn=978-0-309-10851-5}}</ref> A major goal is to preserve the planetary record of natural processes by preventing human-caused microbial introductions, also called [[forward contamination]]. There is abundant evidence as to what can happen when organisms from regions on Earth that have been isolated from one another for significant periods of time are introduced into each other's environment. Species that are constrained in one environment can thrive - often out of control - in another environment much to the detriment of the original species that were present. In some ways this problem could be compounded if life forms from one planet were introduced into the totally alien ecology of another world.<ref name='Cowing'>{{cite web | url = http://astrobiology.com/2013/04/planetary-protection-a-work-in-progress.html | title = Planetary Protection: A Work in Progress | accessdate = 2013-06-02 | first = Keith |last=Cowing | date = April 11, 2013 | work = Astrobiology}}</ref>

The prime concern of hardware contaminating Mars, derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name=Beaty/><ref name=Debus>{{cite journal |bibcode=2005AdSpR..35.1648D |title=Estimation and assessment of Mars contamination |author1=Debus |first1=A. |volume=35 |year=2005 |pages=1648–53 |journal=Advances in Space Research |doi=10.1016/j.asr.2005.04.084 |pmid=16175730 |issue=9}}</ref> Hardware includes landers, crashed probes, end of mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on [[Radioresistance|radiation-resistant microorganisms]] including [[Brevundimonas]], [[Rhodococcus]], [[Pseudomonas]] genera and ''[[Deinococcus radiodurans]]'' survival rates under simulated Martian conditions.<ref name='Planetary protection - radiodurans'>{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |author1=Dartnell |first1=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |year=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these this experimental irradiation experiments, combined with previous radiation modeling, indicate that [[Brevundimonas]] sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name='Planetary protection - radiodurans'/> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref>{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' |author1=de la Vega |first1=U. Pogoda |last2=Rettberg |first2=P. |last3=Reitz |first3=G. |volume=40 |year=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations, ''Deinococcus radiodurans'' also failed to grow under low atmospheric pressure, under 0 °C, or in the absence of oxygen.<ref>{{cite journal | title = Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-Enriched Anoxic Atmospheres | journal = Astrobiology | date = February 2013 | first = Andrew C. Schuerger | coauthors = Richard Ulrich, Bonnie J. Berry, and Wayne L. Nicholson. | volume = 13 | issue = 2 | pages = 115–131 | doi = 10.1089/ast.2011.0811 | url = http://online.liebertpub.com/doi/full/10.1089/ast.2011.0811 | accessdate = 2013-07-04}}</ref>

==Life under simulated Martian conditions==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation|simulation time]] of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref>{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last1=de Vera |first1=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |year=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last1=de Vera |first1=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |year=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">[http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ Surviving the conditions on Mars] DLR, 26 April 2012</ref><ref>{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |year=2012 |last1=de Vera |first1=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref>R. de la Torre Noetzel, F.J. Sanchez Inigo, E. Rabbow, G. Horneck, J. P. de Vera, L.G. Sancho [http://norlx51.nordita.org/~brandenb/astrobiology/EANA2012/single_abstracts/Delatorre.pdf Survival of lichens to simulated Mars conditions]{{self-published inline|date=June 2013}}</ref><ref>{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last1=Sánchez |first1=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |year=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce and evolve in that same environment, necessitating further study.

==Missions==

===Mariner 4===
{{Double image|right|Mars m04 11e.jpg|220|Streamlined Islands in Maja Vallis.jpg|200|Mariner Crater, as seen by Mariner 4 in 1965. Pictures like this suggested that Mars is too dry for any kind of life.|Streamlined Islands seen by Viking orbiter showed that large floods occurred on Mars. Image is located in [[Lunae Palus quadrangle]].}}
{{Main| Mariner 4 }}

[[Mariner 4]] probe performed the first successful [[Planetary flyby|flyby]] of the planet Mars, returning the first pictures of the Martian surface in 1965. The photographs showed an arid Mars without rivers, oceans, or any signs of life. Further, it revealed that the surface (at least the parts that it photographed) was covered in craters, indicating a lack of plate tectonics and weathering of any kind for the last 4 billion years. The probe also found that Mars has no [[Magnetosphere|global magnetic field]] that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was able to calculate the [[atmospheric pressure]] on the planet to be about 0.6 kPa (compared to Earth's 101.3 kPa), meaning that liquid water could not exist on the planet's surface.<ref name="chambers"/> After Mariner 4, the search for life on Mars changed to a search for bacteria-like living organisms rather than for multicellular organisms, as the environment was clearly too harsh for these.

===Viking orbiters===
{{Main|Viking program}}
Liquid water is necessary for known life and [[metabolism]], so if water was present on Mars, the chances of it having supported life may have been determinant. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams.<ref>Strom, R.G., Steven K. Croft, and Nadine G. Barlow, "The Martian Impact Cratering Record," Mars, University of Arizona Press, ISBN 0-8165-1257-4, 1992.{{page needed|date=June 2013}}</ref><ref>Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.{{page needed|date=June 2013}}</ref><ref>Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.{{page needed|date=June 2013}}</ref>
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] poses next to a replica of the Viking landers.]]

===Viking experiments===
{{Main|Viking biological experiments}}

The primary mission of the [[Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil because the favorable conditions for the evolution of multicellular organisms ceased some four billion years ago on Mars.<ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> The tests were formulated to look for microbial life similar to that found on Earth. Of the four experiments, only the Labeled Release (LR) experiment returned a positive result, showing increased 14CO2 production on first exposure of soil to water and nutrients. All scientists agree on two points from the Viking missions: that radiolabeled 14CO2 was evolved in the Labeled Release experiment, and that the GC-MS detected no organic molecules. However, there are vastly different interpretations of what those results imply.

One of the designers of the Labeled Release experiment, [[Gilbert Levin]], believes his results are a definitive diagnostic for life on Mars.<ref name="chambers"/> However, this result is disputed by many scientists, who argue that [[superoxidant]] chemicals in the soil could have produced this effect without life being present. An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify [[natural organic matter]], did not detect organic molecules.<ref name="Levin">{{cite journal |bibcode=2007arXiv0705.3176L |arxiv=0705.3176 |title=Analysis of evidence of Mars life |last1=Levin |first1=Gilbert V. |journal=Electroneurobiología |volume=15 |issue=2 |year=2007 |pages=39–47 |url=http://electroneubio.secyt.gov.ar/Gilbert_V_Levin_Seminar_Carnegie_Institution_Washington.htm}}</ref> The results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive.<ref name="chambers"/><ref>{{cite journal |bibcode=1976Sci...194...99K |title=The Viking Biological Investigation: Preliminary Results |last1=Klein |first1=Harold P. |last2=Horowitz |first2=Norman H. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |volume=194 |year=1976 |pages=99–105 |journal=Science |doi=10.1126/science.194.4260.99 |pmid=17793090 |issue=4260}}</ref>

In 2007, during a Seminar of the Geophysical Laboratory of the [[Carnegie Institution]] (Washington, D.C., USA), [[Gilbert Levin]]'s investigation was assessed once more.<ref name="Levin"/> Levin still maintains that his original data were correct, as the positive and negative control experiments were in order.<ref name="Bianciardi-2012">{{cite journal |bibcode=2012IJASS..13...14B |title=Complexity Analysis of the Viking Labeled Release Experiments |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |volume=13 |issue=1 |year=2012 |pages=14–26 |journal=International Journal of Aeronautical and Space Sciences |doi=10.5139/IJASS.2012.13.1.14}}</ref> Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data —reinterpreted mathematically through [[complexity analysis]]— of the [[Viking biological experiments#Labeled Release|Labeled Release experiments]], that may suggest evidence of "extant microbial life on Mars."<ref name="Bianciardi-2012" /><ref name="Discovery-20120412">{{cite web |last=Klotz |first=Irene |title=Mars Viking Robots 'Found Life' |url=http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |date=12 April 2012 |publisher=[[Discovery Channel|DiscoveryNews]] |accessdate=16 April 2012 }}</ref> Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions.<ref name="Discovery-20120412"/>

Ronald Paepe, an [[Edaphology|edaphologist]] (soil scientist), communicated to the European Geosciences Union Congress that the discovery of the recent detection of [[silicate minerals]] on Mars may indicate [[pedogenesis]], or soil development processes, extended over the entire surface of Mars.<ref name="Paepe">{{cite journal |title=The Red Soil on Mars as a proof for water and vegetation! |journal=Geophysical Research Abstracts |year=2007 |first=Ronald |last=Paepe |volume=9 |issue=1794 |url=http://www.cosis.net/abstracts/EGU2007/01794/EGU2007-J-01794.pdf}}</ref> Paepe's interpretation views most of Mars surface as active soil, colored red by eons of widespread wearing by water, [[vegetation]] and microbial activity.<ref name="Paepe"/>

A research team from the [[National Autonomous University of Mexico]] headed by Rafael Navarro-González, concluded that the equipment (TV-GC-MS) used by the [[Viking program]] to search for organic molecules, may not be sensitive enough to detect low levels of organics.<ref name="Navarro">{{cite journal |bibcode=2006PNAS..10316089N |title=The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results |last1=Navarro-González |first1=Rafael |last2=Navarro |first2= Karina F. |last3=de la Rosa |first3=José |last4=Iñiguez |first4=Enrique |last5=Molina |first5=Paola |last6=Miranda |first6=Luis D. |last7=Morales |first7=Pedro |last8=Cienfuegos |first8=Edith |last9=Coll |first9=Patrice |volume=103 |year=2006 |pages=16089–94 |journal=Proceedings of the National Academy of Sciences |doi=10.1073/pnas.0604210103 |issue=44 |jstor=30052117 |pmid=17060639 |pmc=1621051}}</ref> Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions, so Navarro-González suggests that the design of future organic instruments for Mars should include other methods of detection.

==== ''Gillevinia straata'' ====
The claim for life on Mars, in the form of ''Gillevinia straata'', is based on old data reinterpreted as sufficient evidence of life, mainly by [[Gilbert Levin]],<ref name="Levin"/> Rafael Navarro-González<ref name="Navarro"/> and Ronalds Paepe.<ref name="Paepe"/> The evidence supporting the existence of ''Gillevinia straata'' microorganisms relies on the data collected by the two Mars ''Viking'' landers that searched for [[biosignature]]s of life, but the analytical results were, officially, inconclusive.<ref name="chambers"/>

In 2006, [[Mario Crocco]], a neurobiologist at the [[Borda Hospital|Neuropsychiatric Hospital Borda]] in [[Buenos Aires]], [[Argentina]], proposed the creation of a new [[Taxonomy (biology)|nomenclatural rank]] that classified the Viking landers' results as 'metabolic' and therefore belonging to a form of life. Crocco proposed to create new biological ranking categories ([[taxon|taxa]]), in the new [[kingdom (biology)|kingdom]] system of life, in order to be able to accommodate the genus of Martian microorganisms. Crocco proposed the following taxonomical entry:<ref>{{Cite journal |title=Los taxones mayores de la vida orgánica y la nomenclatura de la vida en Marte: primera clasificación biológica de un organismo marciano |journal=Electroneurobiología |date=April 14, 2007 |first=Mario |last=Crocco |volume=15 |issue=2 |pages=1–34 |url=http://electroneubio.secyt.gov.ar/First_biological_classification_Martian_organism.htm |accessdate=August 14, 2008 |language=Spanish |trans_title=The higher taxa of organic life and nomenclature of life on Mars: first biological classification of a Martian organism}}</ref>
* Organic life system: Solaria
* [[Biosphere]]: Marciana
* [[kingdom (biology)|Kingdom]]: Jakobia (named after neurobiologist Christfried Jakob)
* [[Genus]] and [[species]]: ''Gillevinia straata''

As a result, the hypothetical ''Gillevinia straata'' would not be a bacterium (which rather is a terrestrial taxon), but a member of the kingdom 'Jakobia' in the biosphere 'Marciana' of the 'Solaria' system. The intended effect of the new nomenclature was to reverse the burden of proof concerning the life issue, but the taxonomy proposed by Crocco has not been accepted by the scientific community and is considered a single ''[[nomen nudum]]''. Further, no Mars mission has found traces of [[biomolecules]].<ref>''[http://seedmagazine.com/content/article/what_life_leaves_behind/ What Life Leaves Behind]'' by Veronique Greenwood.</ref><ref>[http://www.astronomynow.com/news/n1305/22organics/#.UczPFZ0o7XI Curiosity tasked with hunting for elusive Mars organics]. Astronomy Now. 22 May 2013</ref>

[[File:Pia09344.jpg|thumb|left|An artist's concept of the Phoenix spacecraft]]

=== Phoenix lander, 2008 ===
{{Main|Phoenix (spacecraft)}}
The [[Phoenix (spacecraft)|Phoenix]] mission landed a robotic spacecraft in the polar region of Mars on May 25, 2008 and it operated until November 10, 2008. One of the mission's two primary objectives was to search for a "habitable zone" in the Martian [[regolith]] where microbial life could exist, the other main goal being to study the [[Geology|geological]] history of water on Mars. The lander has a 2.5 meter robotic arm that was capable of digging shallow trenches in the regolith. There was an electrochemistry experiment which analysed the [[ion]]s in the regolith and the amount and type of [[antioxidant]]s on Mars. The [[Viking program]] data indicate that oxidants on Mars may vary with latitude, noting that [[Viking 2]] saw fewer oxidants than [[Viking 1]] in its more northerly position. Phoenix landed further north still.<ref name="MarsDaily">[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>
Phoenix's preliminary data revealed that Mars soil contains [[perchlorate]], and thus may not be as life-friendly as thought earlier.<ref>{{Cite news|first=|last=|coauthors=|authorlink=|title=NASA Spacecraft Confirms Perchlorate on Mars|date=August 5, 2008|publisher=NASA|url=http://www.nasa.gov/mission_pages/phoenix/multimedia/audioclips-20080805.html|work=NASA|pages=|accessdate=January 28, 2009|language=}}</ref><ref>{{Cite web|url=http://www.latimes.com/news/printedition/asection/la-sci-phoenix6-2008aug06,0,4986721.story|title=Perchlorate found in Martian soil|date=August 6, 2008|publisher=Los Angeles Times|last=Johnson|first=John}}</ref><ref>{{Cite web|url=http://www.sciencedaily.com/releases/2008/08/080805192122.htm|publisher=Science Daily|date=August 6, 2008|title=Martian Life Or Not? NASA's ''Phoenix'' Team Analyzes Results}}</ref> The [[pH]] and salinity level were viewed as benign from the standpoint of biology. The analysers also indicated the presence of bound water and CO2.<ref>{{Cite web|last=Lakdawalla|first=Emily|title=''Phoenix'' sol 30 update: Alkaline soil, not very salty, "nothing extreme" about it!|work=[http://planetary.org/blog/ The Planetary Society weblog]|publisher=[[Planetary Society]]|date=June 26, 2008|url=http://www.planetary.org/blog/article/00001526/|accessdate=June 26, 2008}}</ref>

===Mars Science Laboratory===
[[File:PIA16239 High-Resolution Self-Portrait by Curiosity Rover Arm Camera.jpg|thumb|[[Curiosity rover]] self-portrait at ''"[[Rocknest (Mars)|Rocknest]]"'' (October 31, 2012), with the rim of [[Gale Crater]] and the slopes of [[Aeolis Mons]] in the distance.]]
{{main|Mars Science Laboratory|Curiosity rover}}
The [[Mars Science Laboratory]] mission is a [[NASA]] project that launched on November 26, 2011 the ''[[Curiosity rover]]'', a nuclear-powered robotic vehicle, bearing instruments designed to assess past and present [[planetary habitability|habitability]] conditions on Mars.<ref>{{cite web | date=26 November 2011 | url =http://www.nasa.gov/mission_pages/msl/launch/index.html |title = Mars Science Laboratory Launch | accessdate = 2011-11-26 }}</ref><ref name="NYT-MSL">{{cite web|author=[[Associated Press]] |title=NASA Launches Super-Size Rover to Mars: 'Go, Go!'| url=http://www.nytimes.com/aponline/2011/11/26/science/AP-US-SCI-Mars-Rover.html |publisher=[[New York Times]] |date=26 November 2011| accessdate=2011-11-26 }}</ref> The ''Curiosity'' rover landed on Mars on [[Aeolis Palus]] in [[Gale (crater)|Gale Crater]], near [[Aeolis Mons]] (a.k.a.Mount Sharp),<ref name="IAU-20120516">{{cite web|author=USGS| title=Three New Names Approved for Features on Mars| url=http://astrogeology.usgs.gov/HotTopics/index.php?/archives/447-Three-New-Names-Approved-for-Features-on-Mars.html |date=16 May 2012| publisher=[[USGS]]| accessdate=28 May 2012}}</ref><ref name="NASA-20120327">{{cite web |author=NASA Staff|title='Mount Sharp' on Mars Compared to Three Big Mountains on Earth| url=http://www.nasa.gov/mission_pages/msl/multimedia/pia15292-Fig2.html |date=27 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="NASA-20120328">{{cite web |last=Agle|first=D. C.|title='Mount Sharp' On Mars Links Geology's Past and Future| url=http://www.nasa.gov/mission_pages/msl/news/msl20120328.html| date=28 March 2012 |publisher=[[NASA]] |accessdate=31 March 2012}}</ref><ref name="Space-20120329">{{cite web| author=Staff |title=NASA's New Mars Rover Will Explore Towering 'Mount Sharp'| url=http://www.space.com/15097-mars-mountain-sharp-curiosity-rover.html |date=29 March 2012 |publisher=[[Space.com]] |accessdate=30 March 2012}}</ref> on August 6, 2012.<ref name="Gale Crater">{{cite web |last1=Webster |first1=Guy|last2=Brown |first2=Dwayne |title=NASA's Next Mars Rover To Land At Gale Crater |date=22 July 2011 |publisher=[[NASA JPL]] |url=http://www.jpl.nasa.gov/news/news.cfm?release=2011-222#1 |accessdate=2011-07-22 }}</ref><ref name="Gale Crater2">{{cite web |last1= Chow |first1=Dennis| title=NASA's Next Mars Rover to Land at Huge Gale Crater| url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]]| accessdate=2011-07-22 }}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011| url=http://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |accessdate = 2011-07-22}}</ref>

===Future missions===
* [[ExoMars]] is a European-led multi-spacecraft programme currently under development by the European Space Agency (ESA) and the [[Russian Federal Space Agency]] for launch in 2016 and 2018.<ref name='ESA signed'>{{cite news | title = ExoMars: ESA and Roscosmos set for Mars missions | date = 14 March 2013 | url = http://www.esa.int/Our_Activities/Space_Science/ExoMars_ESA_and_Roscosmos_set_for_Mars_missions | work = European Space Agency (ESA) | accessdate = 2013-03-14}}</ref> Its primary scientific mission will be to search for possible [[biosignature]]s on Mars, past or present. A rover with a {{convert|2|m|ft|abbr5=on}} core drill will be used to sample various depths beneath the surface where liquid water may be found and where microorganisms might survive [[cosmic radiation]].<ref name='Wall'>{{cite news |last=Wall |first=Mike |title=Q & A with Mars Life-Seeker Chris Carr |date=25 March 2011 |url=http://www.space.com/11232-mars-life-evolution-carr-interview.html |work=Space.com | accessdate=2011-03-25}}</ref>
* [[Mars 2020 rover mission]] - The ''Mars 2020 rover mission'' is a [[Mars]] [[Rover (space exploration)|planetary rover]]mission concept under study by [[NASA]] with a possible launch in 2020. It is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]] and potential for preservation of [[biosignature]]s within accessible geological materials.<ref name='Cowing'>{{cite web | url = http://spaceref.com/mars/science-definition-team-for-the-2020-mars-rover.html | title = Science Definition Team for the 2020 Mars Rover | accessdate = 21 December 2012 | first = Keith Cowing | date = 21 December 2012 | work = NASA | publisher = Science Ref}}</ref>
* [[Mars Sample Return Mission]] — The best life detection experiment proposed is the examination on Earth of a soil sample from Mars. However, the difficulty of providing and maintaining life support over the months of transit from Mars to Earth remains to be solved. Providing for still unknown environmental and nutritional requirements is daunting. Should dead organisms be found in a sample, it would be difficult to conclude that those organisms were alive when obtained.

==See also==
* [[Astrobiology]]
* [[Astronomy on Mars]]
* [[Colonization of Mars]]
* [[Extraterrestrial life]]
* [[List of artificial objects on Mars]]
* [[List of rocks on Mars]]
* [[Planetary habitability]]
* [[Seasonal flows on warm Martian slopes]]
* [[Space medicine]]
* [[Terraforming]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.space.com/scienceastronomy/060420_mars_water.html Study Reveals Young Mars Was A Wet World]
* [http://marsprogram.jpl.nasa.gov/overview/ NASA - The Mars Exploration Program]
* [http://news.bbc.co.uk/1/hi/sci/tech/3560867.stm Scientists have discovered that Mars once had saltwater oceans]
* [http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm BBC News: Ammonia on Mars could mean life]
* [http://www.space.com/scienceastronomy/mars_microorganisms_040803.html Scientist says that life on Mars is likely today]
* [http://www.space.com/news/science_top10_041216.html Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science]
* [http://www2.jpl.nasa.gov/snc/nasa1.html Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars]
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000 Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?]
* [http://www.monochrom.at/dark-dune-spots/ Audio interview about "Dark Dune Spots"]
{{Mars}}
{{Extraterrestrial life}}
{{Astrobiology}}
{{portal bar|Mars|Astrobiology}}

{{DEFAULTSORT:Life On Mars}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Mars]]
[[Category:Astronomical controversies]]

{{Link GA|ca}}
{{Link GA|ja}}
{{Link FA|sh}}

OZ-14 Grosa

2013-07-04T03:52:30Z

Someone not using his real name: /* References */ It's a list of products, but clikcing on the OTs-14 from there gives 404, so not very useful now.

{{no footnotes|date=January 2013}}
{{Infobox Weapon
|name=OTs-14 Groza
|image=[[File:ОЦ-14 4.jpg|300px]]
|caption=OTs-14-4A (configuration with grenade launcher)
|origin=[[Russian Federation]] 
|type=[[Assault rifle]]

|is_ranged=yes

|service=1994–present
|used_by=[[Spetsnaz]]
|wars=[[First Chechen War]] [[Second Chechen War]] [[2008 South Ossetia war|2008 South Ossetia War]]

|designer=V.N. Telesh and U.V. Lebedev
|design_date=1990s
|manufacturer=TsKIB SOO
|unit_cost=
|production_date=
|number=
|variants=OTs-14-4A OTs-14-4A-01 OTs-14-4A-02 OTs-14-4A-03

|spec_label=
|weight=2,7 kg (OTs-14-4A-01 and OTs-14-4A-02) 3,6 kg (OTs-14-4A and OTs-14-4A-03)
|length=610 mm (OTs-14-4A) 565 mm (OTs-14-4A-01) 500 mm (OTs-14-4A-02) 720 mm (OTs-14-4A-03)
|part_length=240 mm (Groza-4) 415 mm (Groza-1)
|width=60 mm (OTs-14-4A without a grenade launcher) 75 mm (OTs-14-4A with a grenade launcher mounted) 70 mm (OTs-14-1A without a grenade launcher) 80 mm (OTs-14-1A with a grenade launcher mounted)
|height=294 mm (OTs-14-4A without a grenade launcher) 266 mm (OTs-14-4A with a grenade launcher mounted) 350 mm (OTs-14-1A without a grenade launcher) 320 mm (OTs-14-1A with a grenade launcher mounted)

|cartridge=[[9×39mm|9x39mm]] (Groza-4), [[7.62×39mm|7.62x39mm]] (Groza-1)
|action=[[Gas-operated reloading|Gas-operated]], [[rotating bolt]]
|rate=700 rounds/min (Groza-4), 750 rounds/min (Groza-1)
|velocity=300 m/s (Groza-4), 720 m/s (Groza-1)
|range=200 m (Groza-4), 300 m (Groza-1)
|max_range=400 m (Groza-4), 500 m (Groza-1)
|feed=20-round detachable box magazine (Groza-4), 30-round detachable box magazine for (Groza-1)
|sights=Iron sights, PO4×34
}}

The '''OTs-14 Groza''' (ОЦ-14 "Гроза") is a Russian selective fire [[bullpup]] [[assault rifle]] chambered for the [[7.62×39]] round and the [[9×39mm]] subsonic round. It was developed in the 1990s at the [[TsKIB SOO]] (Central Design and Research Bureau of Sporting and Hunting Arms) in [[Tula, Russia|Tula]], Russia. The weapon is also colloquially known as OC-14 or OTs-14 "Groza" ("[[Thunderstorm]]"). The OTs-14-4A "Groza-4" has one derivative, the TKB-0239 (ТКБ-0239), also known as '''OTs-14-1A "Groza-1"''', chambered for the [[7.62×39mm|7.62x39mm]] round.

== History ==
Work on the OTs-14-4A project began in December 1992. The weapon's chief designers were Valery Telesh, responsible for the [[GP-25|GP-25 and GP-30]] under-barrel grenade launchers, and Yuri Lebedev. The team set out to design an integrated system that would incorporate all the best features of a close combat arm into a single weapon using the [[AK-74#Variants|AKS-74U]] as a starting platform. Prototypes were ready for testing in less than a year and the weapon was ready for production by early 1994.

It was first presented to the public at the MILIPOL [[Moscow]] trade show in April 1994 and adopted by the [[Ministry of Internal Affairs (Russia)|Ministry of Internal Affairs (MVD)]] shortly thereafter. The success of the OTs-14-4A in the hands of MVD personnel brought it to the attention of the [[Ministry of Defence (Russia)|Ministry of Defence (MO)]], who also had a requirement for such a weapon. After a period of testing, the weapon was adopted for [[spetsnaz]] forces and some airborne and specialist front-line combat units such as [[combat engineer]]s. The weapon was originally intended to have used any one of four cartridges: [[5.45×39mm|5.45x39mm]], [[5.56×45mm NATO|5.56x45mm]], [[7.62×39mm|7.62x39mm]] or [[9×39mm|9x39mm]]. That idea was dropped and the assault rifle was originally chambered in 9x39mm to meet the MVD's requirement for a close combat weapon for deployment in [[Chechnya]].

== Design details ==
=== Operating mechanism ===
The OTs-14-4A is a small arms weapon system based on the 5.45x39mm AKS-74U [[carbine]]. It is a [[selective fire]], air-cooled magazine-fed rifle with a [[Gas-operated reloading|gas-actuated]] piston operating system and a [[rotating bolt|rotary bolt]] locking mechanism.

=== Features ===
The OTs-14-4A shares a 75% component commonality with the AKS-74U. The basic components of the weapon are borrowed directly from the AKS-74U assault rifle and slightly modified, simplifying the design as a whole and making the weapon considerably cheaper. The weapon has modular design allowing for assembly of one of four weapon versions depending on the assigned mission. It is configured in a bullpup layout for increased portability and balance. The grip is displaced forward, making the assault rifle compact, suitable for concealed carrying and so well balanced that it can be fired using just one hand, like a pistol.

The weapon fires from a [[closed bolt]] and has a hammer-type firing mechanism. A fire mode selector is provided which also serves as a manual safety catch. The assault rifle is equipped with [[iron sight]]s contained in the carrying handle that consist of an adjustable rear aperture sight on a tangent leaf with range graduations from 50 to 200 m, and a forward post. The grenade launcher is aimed using a folding leaf sight. The weapon will also accept several optical sights, including the [[PSO-1|PSO]] telescopic sights which mount directly onto the carrying handle or, as on early models, onto a bracket on the left side of the [[Receiver (firearms)|receiver housing]]. The OTs-14-4A also has a night sight dovetail that will accept all standard night vision optics.

=== Accessories ===
It is issued in an [[aluminum]] transport case with equipment and accessories for a wide array of tactical situations. Included in the case are two different grip and trigger assemblies, one for use with the modified GP-25/30 grenade launcher and another for use when the launcher is detached. When the grenade launcher is installed, the combined rifle and grenade launcher is operated with a single trigger. A selector switch on left side of the grip near the trigger guard allows the user to select between rifle or grenade barrels. When the grenade launcher is detached, it is replaced by a vertical grip. A [[suppressor]] is also included in the standard kit, as is a quick-change short barrel for use with the suppressor or for when maximum compactness is desired.

=== Variants ===
* '''OTs-14-4A''' - variant with a grenade launcher
* '''OTs-14-4A-01''' - variant with a vertical foregrip
* '''OTs-14-4A-02''' - variant without barrel attachments
* '''OTs-14-4A-03''' - variant with a suppressor

<gallery>
File:ОЦ-14 4.jpg|
File:ОЦ-14 2.jpg|
File:ОЦ-14 3.jpg|
File:ОЦ-14 Гроза.jpg|
</gallery>

=== Advantages ===
* Weapon compactness, relatively small weight and bullpup scheme provided a good balance and reduced barrel jump.
* It is as reliable as the [[Kalashnikov assault rifle]], as it is based on the same internal design.
* [[9×39mm|9x39mm]] SP-5 and SP-6 subsonic rounds along with the attachable suppressor provide quite silent shooting.
* Heavy 9 mm bullet (16 g) provides high killing, and stopping power.
* Good accuracy, along with the high killing and penetration of bullets and a decent rate of fire, provides a reliable engagement of the targets in bulletproof vests of third-class protection, and targets behind cover.
* Modular design allows you to convert the complex into an assault rifle, a [[CQB]] assault rifle, a grenade launcher and a sniper rifle.
* The 9x39mm rounds' subsonic velocity actually makes them surprisingly viable for CQB situations, and the Groza is no exception.

=== Disadvantages ===
[[File:Beslan-spetznaz.jpg|thumb|Member of an unidentified Russian special force carrying suppressed OC-14 (on his back) during the [[Beslan school hostage crisis]] in 2004]]

* Short aiming line make aiming problematic. Low flatness of the [[9×39mm|9x39mm]] round, makes it difficult to choose the aiming point.
* Bullpup scheme causes difficulties with changing of the magazine.
* The "4" variant has a 20-round low capacity magazine.
* Using of a single trigger for both assault rifle and grenade launcher slows down switching from grenade launcher to assault rifle and back.
* The sidemounts for different optics must be set up additionally.
* Variants without grenade launcher have a shifted gravity center.
* Left-handed shooting is impossible, because of an extractor situated close to the face on the right side of the weapon.
* The gravity center is situated in the pistol grip and loads the right hand, that lessens the accuracy.

=== See also ===
*[[9A-91]]
*[[AK-9]]
*[[AS Val|AS]]
*[[OTs-12 assault rifle|OTs-12]]
*[[SR-3 Vikhr|SR-3]]
*[[TKB-022PM]]
*[[TKB-059]]
*[[TKB-0146]]
*[[VSK-94]]
*[[VSS Vintorez|VSS]]

== See also ==
*[[List of Russian weaponry]]

== References ==
* [http://www.sinopa.ee/sor/bo001/bo04av/bo04av05/oc14.htm Project "Groza"]
* [http://www.enemyforces.com/firearms/groza.htm EnemyForces]
* [http://world.guns.ru/assault/as09-e.htm Modern Firearms]
* [http://weapon.at.ua/load/321-1-0-815 Энциклопедия Оружия]
*{{cite book| last = Cutshaw| first = Charlie| authorlink = | coauthors = | year = 1998| chapter =| title = The New World of Russian Small Arms & Ammo| publisher = Paladin Press| location = Boulder, CO| isbn = 0-87364-993-1|pages=21-26}}

{{AK47 derivatives}}
{{Bullpup Firearms}}

[[Category:7.62 mm firearms]]
[[Category:Assault rifles]]
[[Category:Bullpup firearms]]
[[Category:Kalashnikov derivatives]]
[[Category:Weapons of Russia]]

OZ-14 Grosa

2013-07-04T03:51:07Z

Someone not using his real name: /* Bibliography */ book's a bit dated, but lacking much else in English on this page...

{{no footnotes|date=January 2013}}
{{Infobox Weapon
|name=OTs-14 Groza
|image=[[File:ОЦ-14 4.jpg|300px]]
|caption=OTs-14-4A (configuration with grenade launcher)
|origin=[[Russian Federation]] 
|type=[[Assault rifle]]

|is_ranged=yes

|service=1994–present
|used_by=[[Spetsnaz]]
|wars=[[First Chechen War]] [[Second Chechen War]] [[2008 South Ossetia war|2008 South Ossetia War]]

|designer=V.N. Telesh and U.V. Lebedev
|design_date=1990s
|manufacturer=TsKIB SOO
|unit_cost=
|production_date=
|number=
|variants=OTs-14-4A OTs-14-4A-01 OTs-14-4A-02 OTs-14-4A-03

|spec_label=
|weight=2,7 kg (OTs-14-4A-01 and OTs-14-4A-02) 3,6 kg (OTs-14-4A and OTs-14-4A-03)
|length=610 mm (OTs-14-4A) 565 mm (OTs-14-4A-01) 500 mm (OTs-14-4A-02) 720 mm (OTs-14-4A-03)
|part_length=240 mm (Groza-4) 415 mm (Groza-1)
|width=60 mm (OTs-14-4A without a grenade launcher) 75 mm (OTs-14-4A with a grenade launcher mounted) 70 mm (OTs-14-1A without a grenade launcher) 80 mm (OTs-14-1A with a grenade launcher mounted)
|height=294 mm (OTs-14-4A without a grenade launcher) 266 mm (OTs-14-4A with a grenade launcher mounted) 350 mm (OTs-14-1A without a grenade launcher) 320 mm (OTs-14-1A with a grenade launcher mounted)

|cartridge=[[9×39mm|9x39mm]] (Groza-4), [[7.62×39mm|7.62x39mm]] (Groza-1)
|action=[[Gas-operated reloading|Gas-operated]], [[rotating bolt]]
|rate=700 rounds/min (Groza-4), 750 rounds/min (Groza-1)
|velocity=300 m/s (Groza-4), 720 m/s (Groza-1)
|range=200 m (Groza-4), 300 m (Groza-1)
|max_range=400 m (Groza-4), 500 m (Groza-1)
|feed=20-round detachable box magazine (Groza-4), 30-round detachable box magazine for (Groza-1)
|sights=Iron sights, PO4×34
}}

The '''OTs-14 Groza''' (ОЦ-14 "Гроза") is a Russian selective fire [[bullpup]] [[assault rifle]] chambered for the [[7.62×39]] round and the [[9×39mm]] subsonic round. It was developed in the 1990s at the [[TsKIB SOO]] (Central Design and Research Bureau of Sporting and Hunting Arms) in [[Tula, Russia|Tula]], Russia. The weapon is also colloquially known as OC-14 or OTs-14 "Groza" ("[[Thunderstorm]]"). The OTs-14-4A "Groza-4" has one derivative, the TKB-0239 (ТКБ-0239), also known as '''OTs-14-1A "Groza-1"''', chambered for the [[7.62×39mm|7.62x39mm]] round.

== History ==
Work on the OTs-14-4A project began in December 1992. The weapon's chief designers were Valery Telesh, responsible for the [[GP-25|GP-25 and GP-30]] under-barrel grenade launchers, and Yuri Lebedev. The team set out to design an integrated system that would incorporate all the best features of a close combat arm into a single weapon using the [[AK-74#Variants|AKS-74U]] as a starting platform. Prototypes were ready for testing in less than a year and the weapon was ready for production by early 1994.

It was first presented to the public at the MILIPOL [[Moscow]] trade show in April 1994 and adopted by the [[Ministry of Internal Affairs (Russia)|Ministry of Internal Affairs (MVD)]] shortly thereafter. The success of the OTs-14-4A in the hands of MVD personnel brought it to the attention of the [[Ministry of Defence (Russia)|Ministry of Defence (MO)]], who also had a requirement for such a weapon. After a period of testing, the weapon was adopted for [[spetsnaz]] forces and some airborne and specialist front-line combat units such as [[combat engineer]]s. The weapon was originally intended to have used any one of four cartridges: [[5.45×39mm|5.45x39mm]], [[5.56×45mm NATO|5.56x45mm]], [[7.62×39mm|7.62x39mm]] or [[9×39mm|9x39mm]]. That idea was dropped and the assault rifle was originally chambered in 9x39mm to meet the MVD's requirement for a close combat weapon for deployment in [[Chechnya]].

== Design details ==
=== Operating mechanism ===
The OTs-14-4A is a small arms weapon system based on the 5.45x39mm AKS-74U [[carbine]]. It is a [[selective fire]], air-cooled magazine-fed rifle with a [[Gas-operated reloading|gas-actuated]] piston operating system and a [[rotating bolt|rotary bolt]] locking mechanism.

=== Features ===
The OTs-14-4A shares a 75% component commonality with the AKS-74U. The basic components of the weapon are borrowed directly from the AKS-74U assault rifle and slightly modified, simplifying the design as a whole and making the weapon considerably cheaper. The weapon has modular design allowing for assembly of one of four weapon versions depending on the assigned mission. It is configured in a bullpup layout for increased portability and balance. The grip is displaced forward, making the assault rifle compact, suitable for concealed carrying and so well balanced that it can be fired using just one hand, like a pistol.

The weapon fires from a [[closed bolt]] and has a hammer-type firing mechanism. A fire mode selector is provided which also serves as a manual safety catch. The assault rifle is equipped with [[iron sight]]s contained in the carrying handle that consist of an adjustable rear aperture sight on a tangent leaf with range graduations from 50 to 200 m, and a forward post. The grenade launcher is aimed using a folding leaf sight. The weapon will also accept several optical sights, including the [[PSO-1|PSO]] telescopic sights which mount directly onto the carrying handle or, as on early models, onto a bracket on the left side of the [[Receiver (firearms)|receiver housing]]. The OTs-14-4A also has a night sight dovetail that will accept all standard night vision optics.

=== Accessories ===
It is issued in an [[aluminum]] transport case with equipment and accessories for a wide array of tactical situations. Included in the case are two different grip and trigger assemblies, one for use with the modified GP-25/30 grenade launcher and another for use when the launcher is detached. When the grenade launcher is installed, the combined rifle and grenade launcher is operated with a single trigger. A selector switch on left side of the grip near the trigger guard allows the user to select between rifle or grenade barrels. When the grenade launcher is detached, it is replaced by a vertical grip. A [[suppressor]] is also included in the standard kit, as is a quick-change short barrel for use with the suppressor or for when maximum compactness is desired.

=== Variants ===
* '''OTs-14-4A''' - variant with a grenade launcher
* '''OTs-14-4A-01''' - variant with a vertical foregrip
* '''OTs-14-4A-02''' - variant without barrel attachments
* '''OTs-14-4A-03''' - variant with a suppressor

<gallery>
File:ОЦ-14 4.jpg|
File:ОЦ-14 2.jpg|
File:ОЦ-14 3.jpg|
File:ОЦ-14 Гроза.jpg|
</gallery>

=== Advantages ===
* Weapon compactness, relatively small weight and bullpup scheme provided a good balance and reduced barrel jump.
* It is as reliable as the [[Kalashnikov assault rifle]], as it is based on the same internal design.
* [[9×39mm|9x39mm]] SP-5 and SP-6 subsonic rounds along with the attachable suppressor provide quite silent shooting.
* Heavy 9 mm bullet (16 g) provides high killing, and stopping power.
* Good accuracy, along with the high killing and penetration of bullets and a decent rate of fire, provides a reliable engagement of the targets in bulletproof vests of third-class protection, and targets behind cover.
* Modular design allows you to convert the complex into an assault rifle, a [[CQB]] assault rifle, a grenade launcher and a sniper rifle.
* The 9x39mm rounds' subsonic velocity actually makes them surprisingly viable for CQB situations, and the Groza is no exception.

=== Disadvantages ===
[[File:Beslan-spetznaz.jpg|thumb|Member of an unidentified Russian special force carrying suppressed OC-14 (on his back) during the [[Beslan school hostage crisis]] in 2004]]

* Short aiming line make aiming problematic. Low flatness of the [[9×39mm|9x39mm]] round, makes it difficult to choose the aiming point.
* Bullpup scheme causes difficulties with changing of the magazine.
* The "4" variant has a 20-round low capacity magazine.
* Using of a single trigger for both assault rifle and grenade launcher slows down switching from grenade launcher to assault rifle and back.
* The sidemounts for different optics must be set up additionally.
* Variants without grenade launcher have a shifted gravity center.
* Left-handed shooting is impossible, because of an extractor situated close to the face on the right side of the weapon.
* The gravity center is situated in the pistol grip and loads the right hand, that lessens the accuracy.

=== See also ===
*[[9A-91]]
*[[AK-9]]
*[[AS Val|AS]]
*[[OTs-12 assault rifle|OTs-12]]
*[[SR-3 Vikhr|SR-3]]
*[[TKB-022PM]]
*[[TKB-059]]
*[[TKB-0146]]
*[[VSK-94]]
*[[VSS Vintorez|VSS]]

== See also ==
*[[List of Russian weaponry]]

== References ==
* [http://www.tulatskib.ru/HTML_a/sgv_prod_a.html KBP Subsidiary "TsKIB SOO" — official page]
* [http://www.sinopa.ee/sor/bo001/bo04av/bo04av05/oc14.htm Project "Groza"]
* [http://www.enemyforces.com/firearms/groza.htm EnemyForces]
* [http://world.guns.ru/assault/as09-e.htm Modern Firearms]
* [http://weapon.at.ua/load/321-1-0-815 Энциклопедия Оружия]

*{{cite book| last = Cutshaw| first = Charlie| authorlink = | coauthors = | year = 1998| chapter =| title = The New World of Russian Small Arms & Ammo| publisher = Paladin Press| location = Boulder, CO| isbn = 0-87364-993-1|pages=21-26}}

{{AK47 derivatives}}
{{Bullpup Firearms}}

[[Category:7.62 mm firearms]]
[[Category:Assault rifles]]
[[Category:Bullpup firearms]]
[[Category:Kalashnikov derivatives]]
[[Category:Weapons of Russia]]

OZ-14 Grosa

2013-07-04T03:18:29Z

Someone not using his real name: /* See also */ *TKB-0146

{{no footnotes|date=January 2013}}
{{Infobox Weapon
|name=OTs-14 Groza
|image=[[File:ОЦ-14 4.jpg|300px]]
|caption=OTs-14-4A (configuration with grenade launcher)
|origin=[[Russian Federation]] 
|type=[[Assault rifle]]

|is_ranged=yes

|service=1994–present
|used_by=[[Spetsnaz]]
|wars=[[First Chechen War]] [[Second Chechen War]] [[2008 South Ossetia war|2008 South Ossetia War]]

|designer=V.N. Telesh and U.V. Lebedev
|design_date=1990s
|manufacturer=TsKIB SOO
|unit_cost=
|production_date=
|number=
|variants=OTs-14-4A OTs-14-4A-01 OTs-14-4A-02 OTs-14-4A-03

|spec_label=
|weight=2,7 kg (OTs-14-4A-01 and OTs-14-4A-02) 3,6 kg (OTs-14-4A and OTs-14-4A-03)
|length=610 mm (OTs-14-4A) 565 mm (OTs-14-4A-01) 500 mm (OTs-14-4A-02) 720 mm (OTs-14-4A-03)
|part_length=240 mm (Groza-4) 415 mm (Groza-1)
|width=60 mm (OTs-14-4A without a grenade launcher) 75 mm (OTs-14-4A with a grenade launcher mounted) 70 mm (OTs-14-1A without a grenade launcher) 80 mm (OTs-14-1A with a grenade launcher mounted)
|height=294 mm (OTs-14-4A without a grenade launcher) 266 mm (OTs-14-4A with a grenade launcher mounted) 350 mm (OTs-14-1A without a grenade launcher) 320 mm (OTs-14-1A with a grenade launcher mounted)

|cartridge=[[9×39mm|9x39mm]] (Groza-4), [[7.62×39mm|7.62x39mm]] (Groza-1)
|action=[[Gas-operated reloading|Gas-operated]], [[rotating bolt]]
|rate=700 rounds/min (Groza-4), 750 rounds/min (Groza-1)
|velocity=300 m/s (Groza-4), 720 m/s (Groza-1)
|range=200 m (Groza-4), 300 m (Groza-1)
|max_range=400 m (Groza-4), 500 m (Groza-1)
|feed=20-round detachable box magazine (Groza-4), 30-round detachable box magazine for (Groza-1)
|sights=Iron sights, PO4×34
}}

The '''OTs-14 Groza''' (ОЦ-14 "Гроза") is a Russian selective fire [[bullpup]] [[assault rifle]] chambered for the [[7.62×39]] round and the [[9×39mm]] subsonic round. It was developed in the 1990s at the [[TsKIB SOO]] (Central Design and Research Bureau of Sporting and Hunting Arms) in [[Tula, Russia|Tula]], Russia. The weapon is also colloquially known as OC-14 or OTs-14 "Groza" ("[[Thunderstorm]]"). The OTs-14-4A "Groza-4" has one derivative, the TKB-0239 (ТКБ-0239), also known as '''OTs-14-1A "Groza-1"''', chambered for the [[7.62×39mm|7.62x39mm]] round.

== History ==
Work on the OTs-14-4A project began in December 1992. The weapon's chief designers were Valery Telesh, responsible for the [[GP-25|GP-25 and GP-30]] under-barrel grenade launchers, and Yuri Lebedev. The team set out to design an integrated system that would incorporate all the best features of a close combat arm into a single weapon using the [[AK-74#Variants|AKS-74U]] as a starting platform. Prototypes were ready for testing in less than a year and the weapon was ready for production by early 1994.

It was first presented to the public at the MILIPOL [[Moscow]] trade show in April 1994 and adopted by the [[Ministry of Internal Affairs (Russia)|Ministry of Internal Affairs (MVD)]] shortly thereafter. The success of the OTs-14-4A in the hands of MVD personnel brought it to the attention of the [[Ministry of Defence (Russia)|Ministry of Defence (MO)]], who also had a requirement for such a weapon. After a period of testing, the weapon was adopted for [[spetsnaz]] forces and some airborne and specialist front-line combat units such as [[combat engineer]]s. The weapon was originally intended to have used any one of four cartridges: [[5.45×39mm|5.45x39mm]], [[5.56×45mm NATO|5.56x45mm]], [[7.62×39mm|7.62x39mm]] or [[9×39mm|9x39mm]]. That idea was dropped and the assault rifle was originally chambered in 9x39mm to meet the MVD's requirement for a close combat weapon for deployment in [[Chechnya]].

== Design details ==
=== Operating mechanism ===
The OTs-14-4A is a small arms weapon system based on the 5.45x39mm AKS-74U [[carbine]]. It is a [[selective fire]], air-cooled magazine-fed rifle with a [[Gas-operated reloading|gas-actuated]] piston operating system and a [[rotating bolt|rotary bolt]] locking mechanism.

=== Features ===
The OTs-14-4A shares a 75% component commonality with the AKS-74U. The basic components of the weapon are borrowed directly from the AKS-74U assault rifle and slightly modified, simplifying the design as a whole and making the weapon considerably cheaper. The weapon has modular design allowing for assembly of one of four weapon versions depending on the assigned mission. It is configured in a bullpup layout for increased portability and balance. The grip is displaced forward, making the assault rifle compact, suitable for concealed carrying and so well balanced that it can be fired using just one hand, like a pistol.

The weapon fires from a [[closed bolt]] and has a hammer-type firing mechanism. A fire mode selector is provided which also serves as a manual safety catch. The assault rifle is equipped with [[iron sight]]s contained in the carrying handle that consist of an adjustable rear aperture sight on a tangent leaf with range graduations from 50 to 200 m, and a forward post. The grenade launcher is aimed using a folding leaf sight. The weapon will also accept several optical sights, including the [[PSO-1|PSO]] telescopic sights which mount directly onto the carrying handle or, as on early models, onto a bracket on the left side of the [[Receiver (firearms)|receiver housing]]. The OTs-14-4A also has a night sight dovetail that will accept all standard night vision optics.

=== Accessories ===
It is issued in an [[aluminum]] transport case with equipment and accessories for a wide array of tactical situations. Included in the case are two different grip and trigger assemblies, one for use with the modified GP-25/30 grenade launcher and another for use when the launcher is detached. When the grenade launcher is installed, the combined rifle and grenade launcher is operated with a single trigger. A selector switch on left side of the grip near the trigger guard allows the user to select between rifle or grenade barrels. When the grenade launcher is detached, it is replaced by a vertical grip. A [[suppressor]] is also included in the standard kit, as is a quick-change short barrel for use with the suppressor or for when maximum compactness is desired.

=== Variants ===
* '''OTs-14-4A''' - variant with a grenade launcher
* '''OTs-14-4A-01''' - variant with a vertical foregrip
* '''OTs-14-4A-02''' - variant without barrel attachments
* '''OTs-14-4A-03''' - variant with a suppressor

<gallery>
File:ОЦ-14 4.jpg|
File:ОЦ-14 2.jpg|
File:ОЦ-14 3.jpg|
File:ОЦ-14 Гроза.jpg|
</gallery>

=== Advantages ===
* Weapon compactness, relatively small weight and bullpup scheme provided a good balance and reduced barrel jump.
* It is as reliable as the [[Kalashnikov assault rifle]], as it is based on the same internal design.
* [[9×39mm|9x39mm]] SP-5 and SP-6 subsonic rounds along with the attachable suppressor provide quite silent shooting.
* Heavy 9 mm bullet (16 g) provides high killing, and stopping power.
* Good accuracy, along with the high killing and penetration of bullets and a decent rate of fire, provides a reliable engagement of the targets in bulletproof vests of third-class protection, and targets behind cover.
* Modular design allows you to convert the complex into an assault rifle, a [[CQB]] assault rifle, a grenade launcher and a sniper rifle.
* The 9x39mm rounds' subsonic velocity actually makes them surprisingly viable for CQB situations, and the Groza is no exception.

=== Disadvantages ===
[[File:Beslan-spetznaz.jpg|thumb|Member of an unidentified Russian special force carrying suppressed OC-14 (on his back) during the [[Beslan school hostage crisis]] in 2004]]

* Short aiming line make aiming problematic. Low flatness of the [[9×39mm|9x39mm]] round, makes it difficult to choose the aiming point.
* Bullpup scheme causes difficulties with changing of the magazine.
* The "4" variant has a 20-round low capacity magazine.
* Using of a single trigger for both assault rifle and grenade launcher slows down switching from grenade launcher to assault rifle and back.
* The sidemounts for different optics must be set up additionally.
* Variants without grenade launcher have a shifted gravity center.
* Left-handed shooting is impossible, because of an extractor situated close to the face on the right side of the weapon.
* The gravity center is situated in the pistol grip and loads the right hand, that lessens the accuracy.

=== See also ===
*[[9A-91]]
*[[AK-9]]
*[[AS Val|AS]]
*[[OTs-12 assault rifle|OTs-12]]
*[[SR-3 Vikhr|SR-3]]
*[[TKB-022PM]]
*[[TKB-059]]
*[[TKB-0146]]
*[[VSK-94]]
*[[VSS Vintorez|VSS]]

== See also ==
*[[List of Russian weaponry]]

== References ==
* [http://www.tulatskib.ru/HTML_a/sgv_prod_a.html KBP Subsidiary "TsKIB SOO" — official page]
* [http://www.sinopa.ee/sor/bo001/bo04av/bo04av05/oc14.htm Project "Groza"]
* [http://www.enemyforces.com/firearms/groza.htm EnemyForces]
* [http://world.guns.ru/assault/as09-e.htm Modern Firearms]
* [http://weapon.at.ua/load/321-1-0-815 Энциклопедия Оружия]

== Bibliography ==
*{{cite book| last = Cutshaw| first = Charlie| authorlink = | coauthors = | year = 1998| chapter =| title = The New World of Russian Small Arms & Ammo| publisher = Paladin Press| location = Boulder, CO| isbn = 0-87364-993-1}}

{{AK47 derivatives}}
{{Bullpup Firearms}}

[[Category:7.62 mm firearms]]
[[Category:Assault rifles]]
[[Category:Bullpup firearms]]
[[Category:Kalashnikov derivatives]]
[[Category:Weapons of Russia]]