View source for Styx (moon)

{{short description|Small natural satellite of Pluto}}
{{Good article}}
{{Use dmy dates|date=June 2023}}
{{Infobox planet
| name                 = Styx 
| image                = Styx (moon).jpg
| caption              = Pluto's moon Styx, as seen by the ''[[New Horizons]]'' spacecraft on 13 July 2015, from a distance of 632,000&nbsp;km
| discovery_ref        =
| discoverer           = [[Mark R. Showalter|Showalter, M. R.]] et al.
| discovery_site       = [[Hubble Space Telescope]]
| discovered =
  {{plainlist |
* 26 June 2012
* (verified 7 July 2012)
  }}
| discovery_method     = Photographic
| mpc_name             = Pluto V
| alt_names            = S/2012 (134340) 1<br/>S/2012 P 1<ref name=Sheppard>[[Scott S. Sheppard]], [https://sites.google.com/carnegiescience.edu/sheppard/moons/plutomoons Pluto Moons]</ref>
| pronounced           = {{IPAc-en|'|s|t|ɪ|k|s}}<ref>{{OED|Styx}}</ref>
| adjective            = Stygian {{IPAc-en|ˈ|s|t|ɪ|dʒ|i|ə|n}}<ref>{{OED|Stygian}}</ref>
| named_after          = [[Styx|Στύξ]] ''Styx''
| orbit_ref            = <ref name="ShowalterHamilton2015"/>
| epoch                =
| periapsis            =
| apoapsis             =
| semimajor            = {{val|42656|78|u=km}}
| eccentricity         = {{val|0.005787|0.001144}}
| period               = {{val|20.16155|0.00027|ul=d}}
| synodic_period       =
| avg_speed            =
| mean_anomaly         =
| inclination          = {{val|0.809|0.162|ul=deg}}
| angular_dist         =
| asc_node             =
| arg_peri             =
| satellite_of         = Pluto
| dimensions           = {{val|16|x|9|x|8}} km<ref name=LPSC>{{cite web|url=https://www.youtube.com/watch?v=ZtoLw0KWzsU?t=7470|title=Special Session: Planet 9 from Outer Space – Pluto Geology and Geochemistry|publisher=[[Lunar and Planetary Institute]]|via=[[YouTube]]|date=25 March 2016|access-date=27 May 2019}}</ref>
| mass                 = {{val|7.5e15|u=kg}}<ref>{{cite web|last1=Johnston|first1=Robert|title=(134340) Pluto, Charon, Nix, Hydra, Kerberos, and Styx|url=http://www.johnstonsarchive.net/astro/astmoons/am-pluto.html|website=Asteroids with Satellites Database—Johnston's Archive|access-date=7 March 2016}}</ref>
| density              =
| sidereal_day         = 3.24 ± 0.07 d (chaotic)<ref name=LPSC/>
| axial_tilt           = 82°<ref name=Lakdawalla1110>{{cite web|url=http://www.planetary.org/blogs/emily-lakdawalla/2015/dps15-1110-small-moons.html|title=DPS 2015: Pluto's small moons Styx, Nix, Kerberos, and Hydra [UPDATED]|website=planetary.org}}</ref> (to orbital plane)
| albedo               = 0.65 ± 0.07 geometric<ref name=LPSC/>
| single_temperature   =
| spectral_type        =
| magnitude            = {{val|27|0.3}}<ref name="Sanders 2012-07-11" /><ref name="S&T12" />
| abs_magnitude        =
}}

'''Styx''', formal designation '''(134340) Pluto V''',  is a small [[Moons of Pluto|natural satellite of Pluto]] whose discovery was announced on 11 July 2012. It was discovered by use of the [[Hubble Space Telescope]], and is the smallest of the five known moons of [[Pluto]]. It was imaged along with Pluto and Pluto's other moons by the ''[[New Horizons]]'' spacecraft in July 2015, albeit poorly with only a single image of Styx obtained.<ref name=LPSC/>

Styx is the second-closest known satellite to Pluto, and the fifth discovered. It was discovered one year after [[Kerberos (moon)|Kerberos]]. Styx is approximately {{convert|16|km|mi|abbr=on}} across its longest dimension,<ref name=LPSC /> and its orbital period is 20.1 days.

== Discovery and observations ==
[[File:Pluto moon P5 discovery with moons' orbits.jpg|left|thumb|Hubble image of Styx (circled), with the outer moons' orbits shown]]
Styx was discovered by a team led by astronomer [[Mark R. Showalter]], using fourteen sets of images taken between 26 June and 9 July 2012 by the [[Wide Field Camera 3]] fitted to the [[Hubble Space Telescope|Hubble]].<ref name="IAUCirc">{{cite journal|last=Showalter|first=M.R.|author2=Weaver, H. A. |author3=Stern, S. A. |author4=Steffl, A. J. |author5=Buie, M. W. |author6=Merline, W. J. |author7=Mutchler, M. J. |author8=Soummer, R. |author9= Throop, H. B.  |year=2012|title=New Satellite of (134340) Pluto: S/2012 (134340) 1|journal=IAU Circular|volume=9253|page=1|bibcode = 2012IAUC.9253....1S }}</ref> The discovery was announced on 11 July 2012. Styx is about half as bright as the dimmest previously known object in the system, Kerberos, and about one hundred thousandth as bright as Pluto.<ref name="Matson" /> It was designated S/2012 (134340) 1,<ref name="nasa 2012-07-11" /> and informally referred to as P5.<ref name="Matson" /><ref name="chang" /><ref name="guardian 2012-07-11" />

The survey work leading to the discovery of Styx was in preparation for the mission of the uncrewed ''[[New Horizons]]'' spacecraft, which flew by the Pluto system on 14 July 2015. The discovery of another small Plutonian moon heightened concerns that this region of space may harbor more bodies too small to be detected, and that the spacecraft could be damaged by an uncharted body or [[planetary ring]] as it traversed the system at a speed of over 13&nbsp;km/s.<ref name="Sanders 2012-07-11" /><ref name="csmonitor 2012-07-11" /> Tiny moons, such as Saturn's moon [[Pallene (moon)|Pallene]], tend to be associated with tenuous rings or arcs, because their gravity is unable to hold on to material ejected by [[meteoroid]] impacts and such diffuse material represents the chief navigational hazard.<ref name="Redd" /> However, the ''New Horizons'' spacecraft did not detect any smaller moons or rings and it passed through the Pluto system safely.

== Origin ==
The unexpectedly complex moon system around Pluto may be the result of a collision between Pluto and another sizable [[Kuiper belt]] object in the distant past.<ref name="latimes 2012-07-11" /> Pluto's moons may have [[Collisional family|coalesced from the debris]] from such an event, similar to the [[Giant-impact hypothesis|early giant impact]] thought to have created the Earth's [[Moon]]. The orbital resonances may have acted as "ruts" to gather material from the collision.<ref name="Matson" />

== Physical characteristics ==
Styx was originally estimated to have a diameter of between {{convert|10|and|25|km|abbr=on}}.<ref name="hubblesite 2012-07-11" /><ref name="BBC 2012-07-11" /> These figures were inferred from the [[apparent magnitude]] of Styx and by using an estimated [[albedo]] of 0.35 and 0.04 for the lower and upper bounds, respectively.<ref name="Sanders 2012-07-11" /> Measurements made by ''New Horizons'' found an elongated shape with dimensions measuring approximately {{convert|16|×|9|×|8|km|abbr=on}}.<ref name=LPSC /> It is thought to have formed from the debris lofted by a collision, which would have led to losses of the more [[Volatile (astrogeology)|volatile ices]], such as those of [[nitrogen]] and [[Methane clathrate|methane]], in the composition of the impactors. This process is expected to have created a body consisting mainly of [[Ice|water ice]].<ref name="APOD" />

== Orbit ==
{{multiple image | align = right | direction = horizontal | width = 
| header = Animation of moons of Pluto around the [[barycenter]] of Pluto – [[Ecliptic]] plane
| image1 = Animation of moons of Pluto - Front view.gif
| caption1 = Front view
| image2 = Animation of moons of Pluto - Side view.gif 
| caption2 = Side view
| footer ={{legend2|khaki| [[Pluto]]}}{{·}}{{legend2|RoyalBlue| [[Charon (moon)|Charon]]}}{{·}}{{legend2|Lime| Styx}}{{·}}{{legend2|Magenta| [[Nix (moon)|Nix]]}}{{·}}{{legend2|Cyan| [[Kerberos (moon)|Kerberos]]}}{{·}}{{legend2|Orangered| [[Hydra (moon)|Hydra]]}}
}}
Styx orbits the Pluto–Charon [[barycenter]] at a distance of 42,656&nbsp;km,<ref name="ShowalterHamilton2015"/> putting it between the orbits of Charon and [[Nix (moon)|Nix]]. All of [[Moons of Pluto|Pluto's moons]] appear to travel in orbits that are very nearly circular and coplanar, described by Styx's discoverer Mark Showalter as "neatly nested ... a bit like [[Matryoshka doll|Russian dolls]]".<ref name="latimes 2012-07-11" />

It is in an 11:6 [[orbital resonance]] with [[Hydra (moon)|Hydra]], and an 11:9 resonance with Nix (the ratios represent numbers of orbits completed per unit time; the period ratios are the inverses).<ref name="ShowalterHamilton2015"/><ref name="Witze2015">{{cite journal |last1=Witze |first1=Alexandra |title=Pluto's moons move in synchrony |journal=Nature |date=3 June 2015 |doi=10.1038/nature.2015.17681 |s2cid=134519717 }}</ref> As a result of this "Laplace-like" 3-body resonance, it has conjunctions with Nix and Hydra in a 2:5 ratio.

Its orbital period of 20.16155 days<ref name="ShowalterHamilton2015"/> is about 5.0% from a 1:3 mean-motion resonance with the Charon–Pluto orbital period of 6.387 days. With the other moons Nix, [[Kerberos (moon)|Kerberos]], and Hydra, it forms part of an unusual 1:3:4:5:6 (period ratio) sequence of [[orbital resonance#Coincidental 'near' ratios of mean motion|near resonances]].<ref name="Matson" /> In contrast to the orbit, Stygian rotation is [[Chaotic rotation|chaotic]]; like the other small Plutonian moons, Styx is not tidally locked, and its rotation varies over short timescales (at a rate of about 3.239 days at the time of the ''New Horizons'' flyby).<ref name="Lakdawalla1110" />

== Naming ==
Before any of Pluto's moons were discovered, author [[Edmond Hamilton]] referred to three moons of Pluto in his 1940 [[science fiction]] novel ''Calling Captain Future'', naming them {{em|Charon}}, {{em|Styx}}, and {{em|Cerberus}}.<ref name="Codex Regius">{{cite book|title=Pluto & Charon|author=Codex Regius|publisher=CreateSpace Independent Publishing Platform|year=2016|isbn=978-1534960749}}</ref>

Upon discovery, Styx received the [[minor planet designation]] S/2012 (134340) 1 because it was the first satellite (S) discovered orbiting the [[minor planet]] 134340 Pluto in 2012. It is known informally as "P5", meaning the fifth Plutonian moon to be discovered. The designation S/2012 P 1 has sometimes been used, following the pre-2006 format where Pluto was still considered a planet and given its own single-letter abbreviation.<ref name=Sheppard/>

The convention for naming Plutonian moons is to use names associated with the god [[Pluto (god)|Pluto]] in [[classical mythology]]. To decide on names for P4 and P5, [[Mark Showalter]] and the [[SETI Institute]], on behalf of the discovery team, conducted a non-binding internet poll in 2013, in which the general public was invited to vote for their favorite names. The public could choose from a selection of Greek mythological names related to the god Pluto, or could propose their own names.<ref>{{cite web|url=http://heavy.com/news/2013/02/name-plutos-two-new-moons-shatner/ |title=You & William Shatner Can Name Pluto's 2 Newest Moons |date=14 February 2013 |access-date=18 June 2015}}</ref> After the initial announcement, [[William Shatner]], the actor who plays [[Captain James T. Kirk]] in the ''[[Star Trek]]'' franchise, proposed the names Vulcan and Romulus, ostensibly referring to the fire god [[Vulcan (god)|Vulcan]] (a nephew of Pluto), and to [[Romulus]] the founder of Rome, but also alluding to the fictional planets of [[Vulcan (Star Trek planet)|Vulcan]] and [[Romulans#Homeworld|Romulus]] in the ''Star Trek'' universe.<ref name="Marcia Dunn">{{cite news |work=San Francisco Chronicle |title=Capt. Kirk's Vulcan entry wins Pluto moons contest |url=http://www.sfgate.com/news/science/article/Capt-Kirk-s-Vulcan-entry-wins-Pluto-moons-contest-4306638.php |agency=[[Associated Press]] |author=Marcia Dunn |date=25 February 2013 |access-date=25 February 2013 |archive-date=26 February 2013 |archive-url=https://web.archive.org/web/20130226004457/http://www.sfgate.com/news/science/article/Capt-Kirk-s-Vulcan-entry-wins-Pluto-moons-contest-4306638.php |url-status=dead }}</ref><ref name="Nature">{{cite journal |last1=Witze |first1=Alexandra |title=Moon and planet names spark battle |journal=Nature |date=23 April 2013 |volume=496 |issue=7446 |pages=407 |doi=10.1038/496407a |pmid=23619668 |bibcode=2013Natur.496..407W |doi-access=free }}</ref> The 'Romulus' suggestion was discounted, as there is already [[Romulus (moon)|an asteroid moon of that name]],<ref>{{cite news | url=http://www.3news.co.nz/Vulcan-tops-poll-for-moon-name/tabid/1160/articleID/288184/Default.aspx | work=3 News NZ | title='Vulcan' tops poll for moon name | date=26 February 2013 | access-date=26 February 2013 | archive-date=8 August 2014 | archive-url=https://web.archive.org/web/20140808051133/http://www.3news.co.nz/Vulcan-tops-poll-for-moon-name/tabid/1160/articleID/288184/Default.aspx | url-status=dead }}</ref> but Vulcan won the poll after Shatner tweeted about it, with [[Cerberus]] (the dog that guards Pluto's underworld) coming second and [[Styx]] (the goddess of the river of the same name in the underworld) coming third. The winning names were submitted to the [[International Astronomical Union]].<ref name="Nature" />
However, ''Vulcan'' was unacceptable to the IAU because it was not the name of an underworld figure and had already been used for a [[Vulcan (hypothetical planet)|hypothetical planet]] inside the orbit of Mercury, as well as having given its name to the [[vulcanoid]]s.<ref name="Marcia Dunn" /><ref>{{cite web |publisher=SPACE.com |url=http://www.space.com/19943-pluto-moons-name-poll-vulcan.html |title='Vulcan' and 'Cerberus' Win Pluto Moon Naming Poll |author=Miriam Krame |date=25 February 2013 |access-date=25 February 2013 }}</ref><ref>{{cite news|last=Rice|first=Tony|title=Kerberos and Styx named as moons of Pluto|url=http://www.wral.com/-kerberos-and-styx-named-as-moons-of-pluto/12620468/|publisher=WRAL}}</ref>

On 2 July 2013, the IAU announced that it had formally approved the names ''[[Styx]]'' for P5 and ''Kerberos'' for P4.<ref>{{cite web |publisher= [[IAU]] |url= http://www.iau.org/public_press/news/detail/iau1303/ |title= Names for New Pluto Moons Accepted by the IAU After Public Vote |date= 2 July 2013 |access-date= 2 July 2013}}</ref><ref>{{cite web |publisher=[[SETI Institute]] |url=http://www.seti.org/seti-institute/press-release/plutos-smallest-moons-receive-their-official-names |title=Pluto's Smallest Moons Receive Their Official Names |date=2 July 2013 |access-date=2 July 2013 |archive-date=5 July 2013 |archive-url=https://web.archive.org/web/20130705222117/http://www.seti.org/seti-institute/press-release/plutos-smallest-moons-receive-their-official-names |url-status=dead }}</ref>

== See also ==
* [[List of natural satellites]]

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

<ref name="Sanders 2012-07-11">
{{cite web
| last = Sanders
| first = Ray
| date = 11 July 2012
| title = Hubble Space Telescope detects fifth moon of Pluto
| publisher = Phys.org
| url = http://phys.org/news/2012-07-hubble-space-telescope-moon-pluto.html
| access-date = 11 July 2012
}}
</ref>

<ref name="S&T12">
{{cite web
| title = Pluto's Moons: Five and Counting
| publisher = [[Sky & Telescope]]
| date = 11 July 2012
| url = http://www.skyandtelescope.com/community/skyblog/newsblog/Plutos-Moons-Five-and-Counting-162062385.html
}}
</ref>

<!--
<ref name="Than">
{{cite web
| last = Than
| first = K.
| date = 11 September 2006
| title = Pluto is Now Just a Number: 134340
| work = Space.com
| url = http://www.space.com/2876-pluto-number-134340.html
| access-date = 14 July 2012
}}
</ref>-->

<ref name="Matson">
{{cite web
| last = Matson
| first = J.
| date = 11 July 2012
| title = New Moon for Pluto: Hubble Telescope Spots a 5th Plutonian Satellite
| work = [[Scientific American]] web site
| url = http://www.scientificamerican.com/article.cfm?id=pluto-moon-p5
| access-date = 12 July 2012
}}
</ref>

<ref name="nasa 2012-07-11">
{{cite web
| title = Hubble Discovers a Fifth Moon Orbiting Pluto
| date = 11 July 2012
| publisher = NASA
| url = http://www.nasa.gov/mission_pages/hubble/science/new-pluto-moon.html
| access-date = 18 July 2012
}}
</ref>

<ref name="chang">
{{cite news
| last = Chang
| first = Kenneth
| date = 13 July 2012
| title = Pluto jokes resurface after new moon found
| work = The Sydney Morning Herald
| url = http://www.smh.com.au/technology/sci-tech/pluto-jokes-resurface-after-new-moon-found-20120713-2204g.html
| access-date = 18 July 2012
}}
</ref>

<ref name="guardian 2012-07-11">
{{cite news
| title = New moon spotted orbiting Pluto, scientists say
| agency = Associated Press
| date = 11 July 2012
| newspaper = The Guardian
| url = https://www.theguardian.com/science/2012/jul/11/moon-pluto-found-hubble-new?newsfeed=true
| access-date = 18 July 2012
}}
</ref>

<ref name="csmonitor 2012-07-11">
{{cite web
| last = Wall
| first = Mike
| date = 11 July 2012
| title = Hubble telescope spots fifth moon orbiting Pluto
| work = The Christian Science Monitor
| url = https://www.csmonitor.com/Science/2012/0711/Hubble-telescope-spots-fifth-moon-orbiting-Pluto-video
| access-date = 11 July 2012
}}
</ref>

<ref name="Redd">
{{cite web
| last = Redd
| first = N. T.
| title = Pluto's Moons Could Spell Danger for New Horizons Spacecraft
| work = Space.com
| date = 28 November 2011
| url = http://www.space.com/13752-pluto-moons-horizons-spacecraft-danger.html
| access-date = 19 July 2012
}}
</ref>
<!---
<ref name="Lakdawalla">
{{cite web
| last = Lakdawalla
| first = E.
| title = A fifth moon for Pluto, and a possible hazard for New Horizons
| work = Planetary Society blog
| publisher = [[The Planetary Society]]
| date = 17 July 2012
| url = http://www.planetary.org/blogs/emily-lakdawalla/2012/07161247-pluto-fifth-moon-new-horizons-hazard.html
| access-date = 17 July 2012
}}
</ref>
--->
<ref name="hubblesite 2012-07-11">
{{cite web
| publisher = HubbleSite
| date = 11 July 2012
| title = Hubble Discovers a Fifth Moon Orbiting Pluto
| url = http://hubblesite.org/newscenter/archive/releases/2012/32/full/
| access-date = 12 July 2012
}}
</ref>

<ref name="BBC 2012-07-11">
{{cite web
| date = 11 July 2012
| title = Hubble discovers new Pluto moon
| publisher = BBC News
| url = https://www.bbc.co.uk/news/science-environment-18803212
| access-date = 12 July 2012
}}
</ref>

<ref name="APOD">
{{Cite APOD
| title = Fifth Moon Discovered Orbiting Pluto
| date = 16 July 2012
| access-date = 17 July 2012
}}
</ref>

<ref name="latimes 2012-07-11">
{{cite web
| last = Maugh
| first = Thomas H. II
| date = 11 July 2012
| title = Astronomers find fifth moon at Pluto
| work = Los Angeles Times
| url = http://www.latimes.com/news/science/la-sci-sn-pluto-moon-20120711,0,4883068.story
| access-date = 11 July 2012
}}
</ref>

<ref name="ShowalterHamilton2015">
{{cite journal
| last1 = Showalter 
| first1 = M. R.
| author1-link = Mark R. Showalter
| last2 = Hamilton 
| first2 = D. P.
| title = Resonant interactions and chaotic rotation of Pluto's small moons
| journal = Nature
| volume = 522
| issue = 7554
| date = 3 June 2015
| pages = 45–49
| doi = 10.1038/nature14469
| pmid = 26040889
| bibcode = 2015Natur.522...45S 
| s2cid = 205243819
| url = http://planetarynames.wr.usgs.gov/append7.html
| access-date = 3 June 2015
| url-access = subscription
}}</ref>

<!--
<ref name="brozovic">
{{cite journal
| last = Brozovic, M.
| display-authors = etal
| date = 4 February 2015
| title = The orbits and masses of satellites of Pluto
| journal = Icarus
| doi=10.1016/j.icarus.2014.03.015
| bibcode=2015Icar..246..317B
| volume=246
| pages=317–329
}}
</ref>-->

}}

== External links ==

* Showalter, Mark. [http://hubblesite.org/newscenter/archive/releases/2012/32/ Hubble Press Release: Hubble Discovers a Fifth Moon Orbiting Pluto]. 11 July 2012.
* ZME Science [http://www.zmescience.com/space/pluto-fifth-moon-discovered-32143213/ New moon discovered around Pluto&nbsp;– the fifth]. 11 July 2012.

{{2012 in space}}
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{{DEFAULTSORT:S 2012 (134340) 1}}
[[Category:Astronomical objects discovered in 2012|20120626]]
[[Category:Discoveries by the Hubble Space Telescope]]
[[Category:Moons of Pluto]]
[[Category:Moons with a prograde orbit]]