View source for Kerberos (moon)

{{short description|Small natural satellite of Pluto}}
{{About-distinguish2|the fourth moon of Pluto|the asteroid [[1865 Cerberus]]}}
{{good article}}
{{Infobox planet
| name                 = Kerberos
| image                = Kerberos (moon).jpg
| caption              = Kerberos imaged by ''[[New Horizons]]'' on 14 July 2015 from a distance of 396,100 km
| apsis                =
| discovery_ref        = <ref name="telegram" />
| discoverer           = [[Mark R. Showalter|Showalter, M. R.]] et al.
| discovery_site       =
| discovered           = 28 June 2011 <br> (verified 20 July 2011)
| discovery_method     =
| mpc_name             = Pluto IV
| alt_names            = S/2011 (134340) 1<br>S/2011 P 1<ref>[[Scott S. Sheppard]], [https://sites.google.com/carnegiescience.edu/sheppard/moons/plutomoons Pluto Moons]</ref>
| pronounced           = {{IPAc-en|ˈ|k|ɜr|b|ər|ɒ|s|,_|-|ə|s}}
| named_after          = [[Cerberus|Κέρβερος]] ''Kerberos''
| adjective            = Kerberean {{IPAc-en|k|ɜːr|ˈ|b|ɪər|i|ə|n}}<ref>per {{OED|Cerberean}}</ref>
| mp_category          =
| orbit_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}}</ref>
| epoch                =
| periapsis            =
| apoapsis             =
| semimajor            = {{val|57783|19|u=km}}<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=www.planetary.org}}</ref>
| eccentricity         = 0.00328 ± 0.00020
| period               = {{val|32.16756|0.00014|ul=d}}<ref name=Lakdawalla1110/>
| synodic_period       =
| avg_speed            =
| mean_anomaly         =
| inclination          = {{val|0.389|0.037|ul=deg}}
| angular_dist         =
| asc_node             =
| long_periastron      =
| time_periastron      =
| arg_peri             =
| semi-amplitude       =
| satellite_of         = [[Pluto]]
| dimensions           = {{nowrap|1=19 × 10 × 9 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]]|website=[[YouTube]]|date=25 March 2016|access-date=27 May 2019}}</ref>
| circumference        =
| surface_area         =
| volume               =
| mass                 = {{val|1.65e16|u=kg}}{{refn|group=notes|Derived from the published value of ''GM<sub>Kerberos</sub>'' {{=}} {{val|0.0011|0.0006|u=km<sup>3</sup>/s<sup>2</sup>}} <ref>{{cite journal|last1=Brozović|first1=Marina|last2=Showalter|first2=Mark R.|last3=Jacobson|first3=Robert A.|last4=Buie|first4=Marc W.|title=The orbits and masses of satellites of Pluto|journal=Icarus|date=January 2015|volume=246|pages=317–329|doi=10.1016/j.icarus.2014.03.015|bibcode = 2015Icar..246..317B }}</ref> and the relationship ''M<sub>Kerberos</sub>'' {{=}} {{sfrac|''GM<sub>Kerberos</sub>'' |''[[Gravitational constant|G]]''}} }}
| density              =
| surface_grav         =
| escape_velocity      =
| rotation             = 5.31 ± 0.10 d (chaotic)<ref name=LPSC/>
| rot_velocity         =
| axial_tilt           = {{val|96|u=deg}}<ref name="arxiv1604">{{cite journal |last1=Weaver |first1=H. A. |last2=Buie |first2=M. W. |last3=Showalter |first3=M. R. |last4=Stern |first4=S. A. |display-authors=etal|title=The Small Satellites of Pluto as Observed by New Horizons |journal=Science |volume=351 |issue=6279 |pages=aae0030 |date=18 April 2016|arxiv= 1604.05366|doi=10.1126/science.aae0030 |pmid=26989256 |bibcode=2016Sci...351.0030W |s2cid=206646188 }}</ref>
| right_asc_north_pole =
| declination          =
| pole_ecliptic_lat    =
| pole_ecliptic_lon    =
| albedo               = 0.56 ± 0.05<ref name=LPSC/>
| single_temperature   =
| temp_name1           =
| min_temp_1           =
| mean_temp_1          =
| max_temp_1           =
| temp_name2           =
| min_temp_2           =
| mean_temp_2          =
| max_temp_2           =
| spectral_type        =
| magnitude            = {{val|26.1|0.3}}<ref name="telegram" />
| abs_magnitude        =
| angular_size         =
| atmosphere_ref       =
| surface_pressure     =
| scale_height         =
| atmosphere_composition =
}}

'''Kerberos''' is a small [[moons of Pluto|natural satellite of Pluto]], about {{convert|19|km|mi|abbr=on}} in its longest dimension. Kerberos is also the second-smallest moon of [[Pluto]], after [[Styx (moon)|Styx]]. It was the fourth moon of Pluto to be discovered and its existence was announced on 20 July 2011.<ref name="telegram">{{cite web
| last = Showalter | first = M. R. |author2=Hamilton, D. P.
 | title = New Satellite of (134340) Pluto: S/2011 (134340) 1
| work = Central Bureau for Astronomical Telegrams
| publisher = [[International Astronomical Union]]
| date = 20 July 2011 | url = http://www.cbat.eps.harvard.edu/cbet/cbet002769.txt
| access-date = 20 July 2011}}</ref> It was imaged, along with [[Pluto]] and its four other moons, by the ''[[New Horizons]]'' spacecraft in July 2015.<ref Name=UniverseToday>{{cite web|title=Pluto's Moon Nix|author=Cain, Fraser | date=2008| url=http://www.universetoday.com/13905/plutos-moon-nix/}}</ref> The first image of Kerberos from the flyby was released to the public on 22 October 2015.<ref name=":0" />

== Discovery ==
[[File:Pluto P4.jpg|left|thumb|[[Hubble Space Telescope|Hubble]] discovery images of Kerberos]]
Kerberos was discovered by researchers of the Pluto Companion Search Team using the [[Hubble Space Telescope]] on 28 June 2011, using the [[Wide Field Camera 3]], during an attempt to find any [[Planetary ring|rings]] that Pluto might possess.<ref name="hubblesite" /><ref name="Wall">{{cite web | last = Wall | first = M. | title = New Pluto Moon Foreshadows More Surprises for NASA Probe En Route | work = Space.com | date = 20 July 2011| url = http://www.space.com/12372-pluto-fourth-moon-nasa-spacecraft.html | access-date = 21 July 2011}}</ref> The search for rings was motivated in part by a desire to avoid damage to ''[[New Horizons]]'' when it passed through the Pluto system in July 2015.<ref name="ChasingNH" /> Further observations were made on 3 and 18 July 2011 and Kerberos was verified as a new moon on 20 July 2011.<ref name="telegram" /><ref name="autogenerated1">{{cite web |url=http://www.space.com/12356-pluto-fourth-moon-discovery-hubble-photo.html |title=Pluto Has Another Moon, Hubble Photos Reveal {{pipe}} Dwarf Planet Pluto {{pipe}} Pluto's Moons |publisher=Space.com |access-date=12 July 2012 |archive-url=https://web.archive.org/web/20110723185855/http://www.space.com/12356-pluto-fourth-moon-discovery-hubble-photo.html |archive-date=23 July 2011 |url-status=dead }}</ref><!-- https://www.reuters.com/article/2011/07/20/us-space-pluto-idUSTRE76J4L020110720 --> It was later [[precovery|precovered]] or identified in earlier archival Hubble images from 15 February 2006 and 25 June 2010, though Kerberos was obscured by [[diffraction spike]]s in those images.<ref name="earthsky">{{cite web|url=https://earthsky.org/space/hubble-space-telescope-discovers-fourth-moon-of-pluto |title=Hubble Space Telescope discovers fourth moon of Pluto |date=20 July 2011 |publisher=earthsky.org |access-date= 22 February 2019}}</ref> Kerberos's brightness is only about 10% of that of [[Nix (moon)|Nix]], and it was only found because the discovery team took eight-minute exposures; earlier observations had used shorter exposures.<ref name="Lakdawalla" /> It was officially designated S/2011 (134340) 1,<ref name="telegram" /> and was informally referred to as P4.<ref name="Lakdawalla" /> 

== Origin ==
Like Pluto's other moons,<ref name="Stern">{{Cite journal | last = Stern | first = S. A. | author-link = Alan Stern | author2 = Weaver, H. A. | author3 = Steff, A. J. | author4 = Mutchler, M. J. | author5 = Merline, W. J. | author6 = Buie, M. W. | author7 = Young, E. F. | author8 = Young, L. A. | author9 = Spencer, J. R. | title = A giant impact origin for Pluto's small moons and satellite multiplicity in the Kuiper belt | journal = [[Nature (journal)|Nature]] | volume = 439 | issue = 7079 | pages = 946–948 | date = 23 February 2006 | url = http://ns1.plutoportal.net/~layoung/eprint/Stern2006plutosat.pdf | doi = 10.1038/nature04548 | access-date = 20 July 2011 | bibcode = 2006Natur.439..946S | pmid = 16495992 | s2cid = 4400037 | url-status = dead | archive-url = https://web.archive.org/web/20120119001455/http://ns1.plutoportal.net/~layoung/eprint/Stern2006plutosat.pdf | archive-date = 19 January 2012 }}</ref> it is suspected that Kerberos coalesced from the [[Collisional family|debris of a massive collision]] between Pluto and another [[Kuiper belt]] object, similar to the [[Giant-impact hypothesis|giant impact]] thought to have created the [[Moon]].<ref name="hubblesite" >{{cite web | last = Showalter | first = M. | title = NASA's Hubble Discovers Another Moon Around Pluto | publisher = [[hubblesite.org]] | date = 20 July 2011 | url = https://hubblesite.org/contents/news-releases/2011/news-2011-23.html | access-date = 20 July 2011}}</ref>

== Physical characteristics ==
Kerberos has a double-lobed shape and is approximately {{convert|19|km|mi|abbr=on}} across its longest dimension and {{convert|9|km|mi|abbr=on}} across its shortest dimension. It is the second-smallest of Pluto's moons, after Styx. The larger lobe of Kerberos is approximately 8&nbsp;km (5&nbsp;mi) across while the smaller lobe is measured to be approximately {{convert|5|km|mi|abbr=on}} across. The double-lobed shape of Kerberos is likely formed by two smaller objects merged, suggesting that Kerberos along with Pluto's other moons may have been formed by the coalescence of debris around Pluto.<ref>{{Cite web|url = https://solarsystem.nasa.gov/moons/pluto-moons/kerberos/in-depth/|title = Kerberos In Depth|date = December 5, 2017|access-date = February 21, 2019|website = solarsystem.nasa.gov |publisher = NASA}}</ref>

Kerberos has a high [[albedo]] or reflectivity similar to Pluto's other small moons, likely due to the presence of water ice on its surface.<ref>{{Cite web|url = https://cosmosmagazine.com/space/what-are-pluto-s-tiny-moons-made-of|title = New insights into Pluto's outer moons|date = June 17, 2016|access-date = February 21, 2019|website = cosmosmagazine.com|publisher = Cosmos Magazine|archive-date = February 22, 2019|archive-url = https://web.archive.org/web/20190222152020/https://cosmosmagazine.com/space/what-are-pluto-s-tiny-moons-made-of|url-status = dead}}</ref> Before the ''New Horizons'' flyby, Kerberos was initially thought to have a larger size and a darker surface.<ref>{{Cite web|url = http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=330|title = Kerberos Revealed|date = October 22, 2015|access-date = October 22, 2015|website = pluto.jhuapl.edu|publisher = NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute|archive-date = October 29, 2018|archive-url = https://web.archive.org/web/20181029190924/http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=330|url-status = dead}}</ref>

=== Rotation ===

Like the other small moons of Pluto, Kerberos is not [[Tidal locking|tidally locked]] and its rotation is [[Chaos theory|chaotic]], varying quickly over geological timescales. The varying gravitational influences of Pluto and [[Charon (moon)|Charon]] as they orbit their [[barycenter]] causes the chaotic [[Tumbling (rigid body)|tumbling]] of Pluto's small moons, including Kerberos.<ref name="chaos">{{cite web|url=https://www.nasa.gov/press-release/nasa-s-hubble-finds-pluto-s-moons-tumbling-in-absolute-chaos|title=NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos|publisher=NASA|website=www.nasa.gov|date=3 June 2015}}</ref> At the time of the ''New Horizons'' flyby, the rotational period of Kerberos was about 5.33 days and its rotational axis was tilted about 96 degrees to its orbit.<ref name="Lakdawalla1110" /><ref name="arxiv1604"/> The high axial tilt of Kerberos meant that it was rotating sideways relative to its orbit around the Pluto-Charon barycenter.<ref name="arxiv1604"/>

== 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 (moon)|Styx]]}}{{·}}{{legend2|Magenta| [[Nix (moon)|Nix]]}}{{·}}{{legend2|Cyan| Kerberos}}{{·}}{{legend2|Orangered| [[Hydra (moon)|Hydra]]}}
}}
Observations indicate a circular, equatorial orbit around the Pluto-Charon barycenter at a distance of {{convert|57,783|km|mi|abbr=on}}.<ref name="ShowalterHamilton2015"/> All of Pluto's moons including Kerberos have very circular orbits with very low [[orbital inclination]]s to Pluto's equator. Kerberos orbits between Nix and [[Hydra (moon)|Hydra]] and makes a complete orbit around Pluto roughly every 32.167 days.<ref name="telegram" /><ref name="Lakdawalla">{{cite web | last = Lakdawalla | first = E. 
| title = A fourth moon for Pluto
| work = planetary.org
| publisher = [[The Planetary Society]] | date = 20 July 2011
| url = http://www.planetary.org/blogs/emily-lakdawalla/2011/3107.html
| access-date = 20 July 2011}}</ref>

Its orbital period is close to a 1:5 [[orbital resonance]] with [[Charon (moon)|Charon]],<ref name="chaos" /> with the timing discrepancy being about 0.7%.{{refn | <math display="inline">(P_K - 5*P_C)/P_K = 0.0072</math> where <math display="inline">P_K=32.16756\,d</math> is Kerberos's period and <math display="inline">P_C = 6.3872304\,d</math> is Charon's period.| group=notes}} As with the near resonances between Nix or Hydra and Charon (1:4 and 1:6, respectively), determining how close this relationship is to a true resonance will require more-accurate knowledge of Kerberos's orbit, in particular its rate of [[Apsidal precession|precession]].

== Exploration ==
The ''[[New Horizons]]'' spacecraft took images of Kerberos during its flyby of the Pluto system on 14 July 2015. Three months later, on 22 October, the first image of the moon was published. It is the last moon of Pluto to have its image released, revealing that Kerberos was small and had a bright surface contrary to the initial idea that the moon was covered in dark material.<ref name=":0">{{Cite web| title = Last of Pluto's Moons – Mysterious Kerberos – Revealed by New Horizons| url = http://www.nasa.gov/feature/last-of-pluto-s-moons-mysterious-kerberos-revealed-by-new-horizons| website = NASA| access-date = 23 October 2015| first = Tricia| last = Talbert| date = 22 October 2015| archive-date = 23 October 2015| archive-url = https://web.archive.org/web/20151023183655/http://www.nasa.gov/feature/last-of-pluto-s-moons-mysterious-kerberos-revealed-by-new-horizons| url-status = dead}}</ref>

== Naming ==
Upon discovery, Kerberos received the [[minor planet designation]] S/2011 (134340) 1 because it was the first satellite (S) discovered orbiting the [[minor planet]] 134340 Pluto  in 2011. It was initially called "P4", indicating that it was the fourth Plutonian moon to be discovered.<ref name="ChasingNH">{{cite book |last1=Stern |first1=Alan |last2=Grinspoon |first2=David |title=[[Chasing New Horizons]]: Inside the Epic First Mission to Pluto |publisher=Picador |date=May 1, 2018 |chapter=Chapter 12: Into Unknown Danger |isbn=9781250098962}}</ref>
The convention for naming Plutonian moons is to use names associated with the god [[Pluto (god)|Pluto]] in [[classical mythology]].<ref name="IAU-naming" >{{cite web|url=https://www.iau.org/public/themes/naming/#dwarfplanets|title=International Astronomical Union – IAU|website=www.iau.org }}</ref> 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|title=Help Us Name the Moons of Pluto!|url=http://www.plutorocks.com/|archive-url=https://web.archive.org/web/20130216222901/http://www.plutorocks.com/|archive-date=16 February 2013 }}</ref> After the initial announcement, [[William Shatner]], the actor who played 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 |publisher=[[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|author=Alexandra Witze |title=Moon and planet names spark battle : Nature News & Comment |journal=Nature |publisher=[[Nature.com]] |date=23 April 2013 |volume=496 |issue=7446 |pages=407 |doi=10.1038/496407a |pmid=23619668 |bibcode=2013Natur.496..407W |s2cid=33803981 |doi-access=free }}</ref> The "Romulus" suggestion was discounted, because there is already [[Romulus (moon)|an asteroid moon of that name]], 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 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 deity and had already been used for [[Vulcan (hypothetical planet)|a hypothetical planet]] inside the orbit of Mercury, as well as having given its name to the hypothetical [[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> "Cerberus" is already the name of an asteroid, [[1865 Cerberus]], but the Greek form of the name, "Kerberos", was acceptable to the IAU.<ref name="Overbye2013" >{{cite web |work=[[New York Times]] |first=Dennis | last=Overbye| url=https://www.nytimes.com/2013/07/03/science/space/two-of-plutos-moons-get-names-from-greek-mythologys-underworld.html |title=Two of Pluto's Moons Get Names From Greek Mythology's Underworld |date=2 July 2013 |access-date=26 February 2019 }}</ref>

On 2 July 2013, the IAU announced that it formally approved the names Kerberos for P4 and [[Styx (moon)|Styx]] for P5.<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-url=https://web.archive.org/web/20130705222117/http://www.seti.org/seti-institute/press-release/plutos-smallest-moons-receive-their-official-names |archive-date=5 July 2013 |url-status=dead }}</ref>

The names of features on the bodies in the Pluto system are related to mythology and the literature and history of exploration. In particular, the names of features on Kerberos must be related to dogs from literature, mythology, and history.<ref name="IAU-naming" />

The [[Astronomical naming conventions#Natural satellites of planets|provisional designation]] of the satellite varies based on the source used. The [[International Astronomical Union]] announced it as '''S/2011 (134340) 1''',<ref name="telegram" /> whereas the ''[[New Horizons]]'' mission website announced it as '''S/2011 P 1'''.<ref name="NewHorizons">''New Horizons'' news, Johns Hopkins University Applied Physics Laboratory, [http://pluto.jhuapl.edu/news_center/news/20110720.php "Fourth Moon Adds to Pluto's Appeal"] {{Webarchive|url=https://web.archive.org/web/20141113224845/http://pluto.jhuapl.edu/news_center/news/20110720.php |date=2014-11-13 }}, 20 July 2011</ref>

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

== Notes ==
{{reflist|group=notes}}

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

== External links ==

* Showalter, Mark. [http://hubblesite.org/news_release/news/2011-23/76-pluto NASA's Hubble Discovers Another Moon Around Pluto]. 20 July 2011.
* [https://solarsystem.nasa.gov/moons/pluto-moons/kerberos/in-depth/ Kerberos In Depth]. Updated 5 December 2017.
 
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{{Moons of plutoids}}
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[[Category:Moons of Pluto]]
[[Category:Astronomical objects discovered in 2011|20110720]]
[[Category:Cerberus]]