Leben auf dem Mars

2008-08-09T06:47:53Z

67.169.0.250: water ice is known since the days of Viking probes. recent orbiters, rovers, and phoenix landers just further confirm and provide more evidence. Detail account needed.

{{otheruses}}

{{Mergefrom|Gillevinia straata|talk:Gillevinia straata|date=July 2007}}

[[Image:ALH84001 structures.jpg|right|250px|thumb|An electron microscope reveals bacteria-like structures in meteorite fragment [[ALH84001]]]]
[[Image:Moc2 166b msss.gif|thumb|250px|[[Dark dune spot]]s appear year by year]]

Scientists have long speculated about the possibility of '''life on Mars''' owing to the planet's proximity and similarity to [[Earth]]. It remains an open question whether life exists on [[Mars]] now, or existed there in the past.

==Early speculation==
[[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]], [[University of Cambridge|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|canals]] — which were however soon 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. 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.

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">{{Citation
| first = Paul | last = Chambers
| author-link =
| title = Life on Mars; The Complete Story
| place = London
| publisher = Blandford
| year = 1999
| doi = | isbn = 0713727470 }}</ref>
By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal theory.

==Mariner 4==
The photographs taken by the [[Mariner 4]] probe in [[1965]] 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 had no magnetic field that would protect the planet from potentially life-threatening [[cosmic rays]]. The probe was also able to calculate the atmospheric pressure on the planet to be between 4 and 7 millibars, meaning that liquid water could not exist on the planet's surface.<ref name="chambers">lala</ref> 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 experiments==
{{main|Viking biological experiments}}
The primary mission of the [[Viking program|Viking probes]] of the mid-1970s was to carry out experiments designed to detect microorganisms in Martian soil. The big difficulty of this mission was that NASA's knowledge about conditions on Mars' surface was limited to the data returned by Mariner 4, and so the tests were formulated to look for life similar to the life found on Earth. Nevertheless, of the four experiments carried out, the labeled release experiment returned an enigmatic result showing increased CO<sub>2</sub> production on first exposure to water and nutrients. However this sign of life was disputed by many scientists, who argued that [[superoxidant]] chemicals in the soil could have produced this effect without life being present. To counter this it has been argued that the labeled release experiment detected that there were so few metabolising organisms in the martian soil that it would have been impossible for the gas chromatograph to detect them. This view is put forward by one of the designers of the LR experiment, [[Gilbert Levin]], who believes the results of the Viking landers are diagnostic for life on Mars<ref name="chambers">lala</ref>.

A re-analysis of the now 30 year old Viking data in the light of modern knowledge of [[extremophile]] forms of life has suggested that the Viking tests were not sophisticated enough to detect these forms of life, and may even have killed it in the testing procedure.<ref>{{cite news | title=New Analysis of Viking Mission Results Indicates Presence of Life on Mars | publisher=Physorg.com | date=[[January 7]], [[2007]] | url=http://www.physorg.com/news87401064.html | accessdate=2007-03-02 }}</ref><ref name="viking killers">{{cite web|title="Did probes find Martian life ... or kill it off?"|url=http://www.msnbc.msn.com/id/16516952/|Author=Seth Borenstein|publisher=Associated Press via MSNBC|date=2007-01-07|accessdate=2007-05-31}}</ref> The central idea here is that instead of being destroyed by Mars' high levels of hydrogen peroxide and other oxidants, life on Mars may use these chemicals to help them survive. For example hydrogen peroxide would stop water in a cell from freezing down to −50 °C and is [[hygroscopic]], a useful trait on such a dry planet. The researchers cite ''[[Acetobacter peroxidans]]'' as a known example of a microbe that uses hydrogen peroxide in its metabolism.

==Modern findings==
[[Image:History of water on Mars.jpeg|thumb|right|A series of artist's conceptions of hypothetical past water coverage on Mars.]]
Observations made in the late 1990s by the [[Mars Global Surveyor]] confirmed the suspicion that Mars, unlike Earth, no longer possessed a substantial [[Magnetosphere|global magnetic field]], thus allowing potentially life-threatening [[Cosmic ray|cosmic radiation]] to reach the planet's surface. Scientists also speculate that the lack of shielding due to Mars's diminished global magnetic field helped the [[solar wind]] blow away much of [[Atmosphere of Mars|Mars's atmosphere]] over the course of several billion years.

===Meteorites===
In recent years speculation has grown as a result of studies of the [[ALH84001]] [[Mars meteorite]], which concluded that it may have contained [[fossil]]ized [[microbe]]s. Other scientists have subsequently sought to explain these findings on the basis of purely chemical processes. Both remain highly controversial within the scientific community. It has been suggested that other Mars meteorites such as the [[Nakhla meteorite]] have evidence of life also, but as of 2008 no convincing evidence has been forthcoming.{{Fact|date=June 2008}}

===Extremophiles===
Another suggestion of evidence for [[extremophile]]s on Mars comes from analysis of satellite images. It has been proposed that there is a biological origin for the annual appearance and disappearance of [[dark dune spot]]s near the polar regions of Mars.<ref name=fn1>
Gánti, T. et al, [http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1134.pdf "Evidence For Water by Mars Odyssey is Compatible with a Biogenic DDS-Formation Process"]. ([[PDF]]) Lunar and Planetary Science Conference XXXVI (2003)</ref><ref name=fn2>
Horváth, A., et al, [http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1128.pdf "Annual Change ofMartian DDS-Seepages"]. ([[PDF]]) Lunar and Planetary Science Conference XXXVI (2005).</ref>

[[Haloarchaea]] have been proposed as a kind of life that could live on Mars; because the Martian atmosphere has a pressure below the [[triple point]] of water, freshwater species would have no habitat.<ref>{{cite web
| last = DasSarma
| first = Shiladitya
| title = Extreme Halophiles Are Models for Astrobiology
| url=http://www.asm.org/ASM/files/ccLibraryFiles/Filename/000000002127/znw00306000120.pdf | accessdate = 2007-03-17 }}</ref>

===Liquid water on Mars===
No Mars probe since Viking has tested the Martian [[regolith]] directly for signs of life. NASA's recent missions have focused on another question: whether Mars held lakes or oceans of liquid water on its surface in the ancient past. Scientists have found [[hematite]], a mineral that forms in the presence of water. Many scientists have long held this to be almost self-evident based on various geological landforms on the planet, but others have proposed different explanations—wind erosion, oxygen oceans, etc. Thus, the mission of the [[Mars Exploration Rover Mission|Mars Exploration Rovers]] of 2004 was not to look for present or past life, but for evidence of liquid water on the surface of Mars in the planet's ancient past.

In June 2000, evidence for water currently under the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>Malin, Michael C., Edgett, Kenneth S., [http://www.sciencemag.org/cgi/content/full/sci;288/5475/2330 "Evidence for Recent Groundwater Seepage and Surface Runoff on Mars"]. [[Science (journal)|Science]] (2000) Vol. 288. no. 5475, pp. 2330 - 2335.</ref> Deep subsurface [[water]] deposits near the planet's liquid core might form a present-day habitat for life. However, in March 2006, astronomers announced the discovery of similar gullies on the Moon,<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> which is believed never to have had liquid water on its surface. The astronomers suggest that the gullies could be the result of micrometeorite impacts.

In March 2004, NASA announced that its rover ''[[Opportunity rover|Opportunity]]'' had discovered evidence that Mars was, in the ancient past, a wet planet.<ref name=wet>[http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20040302a.html Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet"] - March 2, 2004, [[NASA]] Press release. URL accessed March 19, 2006.</ref> This had raised hopes that evidence of past life might be found on the planet today.

In December 2006, NASA showed images 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 craters and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago, and is perhaps doing so even now. Some researchers were skeptical that liquid water was responsible for the surface feature changes seen by the spacecraft. They said other materials such as sand or dust can flow like a liquid and produce similar results. The findings were published in the [[December 8]] [[2006]] issue of the journal ''[[Science (journal)|Science]]''.<ref>[http://news.yahoo.com/s/ap/20061207/ap_on_sc/mars_water Scientists: Water likely flows on Mars], ''[[Associated Press]]'', accessed on [[December 7]] [[2006]]</ref>

Recent 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 life. Tosca ''et al'' found that the Martian water in the locations they studied all had [[water activity]], a<sub>w</sub> ≤ 0.78 to 0.86 - a level fatal to most Terrestrial life.<ref>Tosca, N J., Knoll, A H., McLennan, S M. ''Water Activity and the Challenge for Life on Early Mars'' Science '''320''', 1204 (2008)</ref>

===Methane on Mars===
''See also: [[Atmosphere_of_Mars#Methane|Methane in the Atmosphere of Mars]]''

===Formaldehyde on Mars===
In February 2005, it was announced that the Planetary Fourier Spectrometer (PFS) on the [[European Space Agency]]'s [[Mars Express Orbiter]] detected substantially more [[formaldehyde]] than anyone had reasonably expected, strongly pointing to other explanations such as microbial life. This claim continues to be widely debated in the scientific community.<ref name=form> [http://www.nature.com/news/2005/050221/full/050221-15.html "Formaldehyde claim inflames martian debate"] - February 25, 2005, http://www.nature.com news story. URL accessed March 19, 2006.</ref> Scientists skeptical to the measurements say that the data from the PFS has been misinterpreted.<ref name=PFS>[http://www.nature.com/news/2005/050905/full/050905-10.html "Martian methane probe in trouble"] - September 25, 2005 http://www.nature.com news story. URL accessed March 19, 2006.</ref>

===Ammonia on Mars===
In the Martian atmosphere [[ammonia]] would be unstable and only last for a few hours. In fact a NASA scientist has said "There are no known ways for ammonia to be present in the Martian atmosphere that do not involve life".<ref name=ammonia>[http://news.bbc.co.uk/1/hi/sci/tech/3896335.stm Ammonia on Mars could mean life]. [[July 14]], [[2004]], [[BBC]] news story. URL accessed March 19, 2006.</ref> For this reason, the detection of ammonia would be extremely important for the debate of whether there is life on Mars.

In 1969, two scientists from the University of California at Berkeley, Dr. [[George C. Pimentel]] and Dr. Kenneth Herr, announced the discovery of methane and ammonia in the Martian atmosphere using Mariner 7 data. The report was withdrawn one month later due to the possibililty of misinterpretation of the absorption of similar spectral bands by frozen carbon dioxide.<ref>"Gas Analysis of Martian Atmosphere Proves Wrong, news article from Rudy Abramson, LA Times, carried by Greeley Tribune, Sept. 13, 1969</ref>

In July 2004 rumors began to circulate that [[Vittorio Formisano]], the scientist in charge of the [[Planetary Fourier Spectrometer]] (PFS), would announce their discovery of ammonia at an upcoming conference, despite briefings by scientists concerned no announcement was made. <ref name=ammonia2>[http://www.nature.com/news/2004/040726/full/040726-3.html "The search for life on Mars"] July 27, 2004, http://www.nature.com news story. URL accessed March 19, 2006. </ref>

===Silica on Mars===
In May [[2007]], the Mars rover [[Spirit rover|Spirit]] disturbed a patch of ground with its inoperative wheel that scientists say shows evidence of a past environment that would have been perfect for microbial life. The feature is reminiscent of the effect of hot spring water or steam coming into contact with volcanic rocks. On Earth, these are locations that tend to teem with bacteria, said rover chief scientist [[Steve Squyres]]. "We're really excited about this," he told a meeting of the American Geophysical Union (AGU). The area is extremely rich in [[silica]] — the main ingredient of window glass. The researchers have now concluded that the bright material must have been produced in one of two ways. One: hot-spring deposits produced when water dissolves silica at one location and then carries it to another (i.e a [[geyser]]). Two:an acidic steam rising through cracks in rocks and stripping them of their mineral components, apart from silica. "The important thing is that whether it is one hypothesis or the other, the implications for the former habitability of Mars are pretty much the same," Professor Squyres explained to BBC News. Hot water provides an environment in which [[microbe]]s can thrive, and the precipitation of that silica entombs and preserves them. Squyres said "You can go to [[hot spring]]s and you can go to [[fumarole]]s and at either place on Earth it is teeming with life — [[Microorganism|microbial life]]." <ref Name="Amos">{{cite web | last = Amos | first = Jonathan | title = Mars robot unearths microbe clue | work = Nasa says its robot rover Spirit has made one of its most significant discoveries on the surface of Mars. | publisher = BBC News | date = 11 December 2007, 05:56 GMT | url = http://news.bbc.co.uk/2/hi/science/nature/7137793.stm | format = web | doi = | accessdate = 2007-12-12 }}</ref><ref Name="20071210a">{{cite web | last = Webster | first = Guy | title = Mars Rover Investigates Signs of Steamy Martian Past | work = Press Release | publisher = Jet Propulsion Laboratory, Pasadena, California | date = December 10, 2007 | url = http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html | format = Web | doi = | accessdate = 2007-12-12 }}</ref>

==Missions==
===Phoenix lander, 2008===
[[Image:Pia09344.jpg|150px|thumb|right|An artist's concept of the Phoenix spacecraft.]]
The [[Phoenix (spacecraft)|Phoenix]] mission landed a telerobot in the polar region of Mars on May 25, 2008. One of the mission's two primary objectives is to search for a 'habitable zone' in the Martian [[regolith]] where microbial life could exist, the other goal being to study the [[Geology|geological]] history of [[water]] on Mars. The lander has a 2.5 meter robotic arm that is capable of digging a 0.5 meter trench in the regolith. The arm is fitted with an arm camera able to verify that there is material in the scoop when returning samples to the lander for analysis – this overcomes an important design flaw in the Viking landers.

The craft has a mass spectrometer capable of detecting organic volatiles up to 10ppb, an optical microscope and an atomic force microscope. There is an electrochemistry experiment which will tell scientists about ions in the regolith and show the amount and type of antioxidants on Mars,<ref>{{cite web | title=Phoenix Mars Lander- Technology | work=Phoenix Mars Lander | url=http://phoenix.lpl.arizona.edu/technology/ | accessdate=2006-04-02}}</ref> if the device works.{{update}} NASA scientist Carol Stoker reports that oxidants on Mars vary with latitude, noting that Viking 2 saw fewer oxidants than Viking 1 because of its more northerly position. Phoenix has landed further north still.<ref>[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref> Rates of sedimentation at the Phoenix landing site are hoped to allow the probe to sample layers that date back at least 50,000 years, and maybe up to a million years. This is important because the climate of Mars has been much warmer in the past and any life could have been more active and widespread, says Stoker.

Unlike the [[Mars Pathfinder]] ''Sojourner'' rover and the [[Mars Exploration Rover]]s, which used [[Airbag#Aerospace and military applications|airbag-cushioned capsules]] to land on Mars, the Phoenix lander landed using [[retro-rocket]]s, as the Viking landers did, despite claims that rocket exhaust may have contaminated the Viking landing sites.<ref name="viking killers">2nd</ref>

===Future missions===
[[NASA]] is planning to launch the [[Astrobiology Field Laboratory]] in 2016, to help answer questions about life on Mars. The Mars Exploration and Payload Analysis Group is responsible for deciding what experiments will fly on the mission.<ref>[http://www.marsdaily.com/reports/Piecing_Together_Life_Potential_999.html Piecing Together Life's Potential]</ref>

==See also==
*[[Planetary habitability]]
*[[Face on Mars]]
*[[Astronomy on Mars]]
*[[List of artificial objects on Mars]]
*[[Martian]]
*[[Terraforming]]
*[[Colonization of Mars]]
*[[Gillevinia straata]]
*[[Terraforming of Mars]]

==References==
<div class="references-small">
<references/>
* [[Alfred Russel Wallace|Wallace, Alfred Russel]]. ''Is Mars habitable? A critical examination of Professor Percival Lowell's book "Mars and its canals," with an alternative explanation, by Alfred Russel Wallace, F.R.S., etc.'' London, Macmillan and co., 1907.
</div>

==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://www.phenomenamagazine.com/0/editorial.asp?aff_id=0&this_cat=Area%2051&action=page&type_id=&cat_id=&obj_id=123 Arthur C. Clarke sees life on Mars]
*[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/2/hi/science/nature/3577551.stm BBC News: Methane on Mars could signal life]
*[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 Scientists say 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"]
* [http://home.comcast.net/~tdehel/site/ Discussion of Phoenix's chances to find life on Mars]

{{Mars}}

[[Category:Astrobiology]]
[[Category:Mars]]
[[Category:Microbiology]]

[[cs:Život na Marsu]]
[[id:Kehidupan di Mars]]
[[it:Vita su Marte]]
[[hu:Élet a Marson]]
[[nl:Leven op Mars]]
[[pt:Vida em Marte]]
[[sk:Život na Marse]]
[[sl:Življenje na Marsu]]

Wikipedia - Benutzerbeiträge [de]

Leben auf dem Mars