Charon (moon) 52838 223689961 2008-07-05T07:56:59Z 98.208.52.107 {{Infobox Planet | name = Charon | bgcolour = #a0ffa0 | image = [[Image:Charon plutoface.png|100px]] | caption = Charon's Pluto-facing hemisphere (determined from brightness variations during Pluto-Charon occultations) | width = 300px | discovery = yes | discoverer = [[James W. Christy]] | discovered = [[June 22]], [[1978]] | orbit_ref = &nbsp;<ref name="Buie06">{{cite journal |author=Marc W. Buie, William M. Grundy, Eliot F. Young, Leslie A. Young, S. Alan Stern |title=''Orbits and photometry of Pluto's satellites: Charon, S/2005 P1, and S/2005 P2'' |journal=Astronomical Journal |year=2006 |volume=132 |pages=290 |url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006AJ....132..290B&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=444b66a47d27727 |id={{arxiv|archive=astro-ph|id=0512491}} |doi=10.1086/504422 }}</ref><!-- http://arxiv.org/pdf/astro-ph/0512491.pdf was A. J. Steffl, M. J. Mutchler, H. A. Weaver, S. A. Stern, D. D. Durda, D. Terrell, W. J. Merline, L. A. Young, E. F. Young, M. W. Buie, and J. R. Spencer, ''New Constraints on Additional Satellites of the Pluto System'', Astronomical Journal, Volume 132, Issue 2, pp. 614-619 (August 2006)--> | epoch = 2,452,600.5 | semimajor = 19,571 ± 4 [[Kilometer|km]]<!--- relative to Pluto centre, as is always the case when the semi-major axis is reported ---> | eccentricity = 0.00000 ± 0.00007 | period = 6.3872304 ± 0.0000011 d<br />(6 d 9 h 17 m 36.7 ± 0.1 s) | inclination = 0°<br />(to Pluto's equator)<br />119.591 ± 0.014°<br />(to Pluto's orbit)<br />112.783 ± 0.014°<br />(to the [[ecliptic]]) <!-- These are all based on the Charon orbit pole of α=133.046±0.014°, δ=-6.145±0.014° in [[J2000]] coordinates ([[International Celestial Reference Frame|ICRF]]) given in Buie et al. (ref name="Buie06")--> | asc_node = 223.046 ± 0.014°<br />(to [[vernal equinox]]) | satellite_of = [[Pluto]] | physical_characteristics = yes | mean_radius = 603.5 ± 1.5 km<ref name="Sicardy06">{{cite journal |author=B. Sicardy et al |title=''Charon’s size and an upper limit on its atmosphere from a stellar occultation'' |journal=Nature |year=2006 |volume=439 |pages=52 |doi= 10.1038/nature04351}}</ref><br />(0.095 Earths) | surface_area = [[1 E13 m²|4.58{{e|6}}]] [[Square kilometre|km²]] | mass = (1.52 ± 0.06){{e|21}} [[Kilogram|kg]]<ref name="Buie06"/><br />(2.54{{e|−4}} Earths)<br />(11.6% of Pluto) | density = 1.65 ± 0.06 [[Gram|g]]/[[Cubic centimeter|cm³]]<ref name="Buie06"/> | surface_grav = 0.278 [[Acceleration|m/s<sup>2</sup>]] | escape_velocity = 0.580 [[km/s]]<br />.36 mi/s | single_temperature = -220°[[Celsius|C]] (53 [[Kelvin|K]]) | rotation = [[Synchronous rotation|synchronous]] | axial_tilt = zero? | albedo = varies between 0.36 and 0.39 | magnitude = 16.8<ref name=magnitude>{{cite web |title=Classic Satellites of the Solar System |url=http://www.oarval.org/ClasSaten.htm |publisher=Observatorio ARVAL |accessdate=2007-10-19}}</ref> | abs_magnitude = 1<ref name=jewitt1000km>{{cite web |date=2008 June |title=The 1000 km Scale KBOs |publisher=Institute for Astronomy (UH) |author=David Jewitt |url=http://www.ifa.hawaii.edu/faculty/jewitt/kb/big_kbo.html |accessdate=2008-06-13}}</ref> | angular_size = 55 milli-arcsec<ref>{{cite web |url = http://www.eso.org/public/outreach/press-rel/pr-2006/pr-02-06.html |title = Stellar occultation allows VLT to determine Charon's size and to put upper limit on its atmosphere |publisher = ESO 02/06 - Science Release |date = 2006-01-04 |accessdate = 2007-10-19 }}</ref> | adjectives = Charonian }} '''Charon''' ({{pronEng|ˈʃɛərən}} ''<small>SHAIR</small>-ən,'' or {{IPA|/ˈkɛərən/}} ''<small>KAIR</small>-ən'' as in {{lang-gr|''Χάρων}})'', discovered in [[1978]], is either the largest moon of [[Pluto]] or one member of a [[double planet|double]] [[dwarf planet]] with Pluto being the other member, depending on the definition employed. With the discovery in [[2005]] of two other moons of Pluto ([[Nix (moon)|Nix]] and [[Hydra (moon)|Hydra]]), Charon is now also referred to as '''Pluto I'''. The ''[[New Horizons]]'' mission is scheduled to visit Charon and Pluto in July 2015. Charon should not be confused with the similarly named [[2060 Chiron|Chiron]], a smaller object in the outer solar system. ==Discovery== Charon was discovered by astronomer [[James Christy]] on [[June 22]], [[1978]], when he was examining highly magnified images of [[Pluto]] on [[photographic plate]]s taken a couple of months before. Christy noticed that a slight bulge appeared periodically. Later, the bulge was confirmed on plates dating back to [[April 29]], [[1965]]. Subsequent observations of Pluto determined that the bulge was due to a smaller accompanying body. The periodicity of the bulge corresponded to Pluto's rotation period, which was previously known from Pluto's [[light curve]]. This indicated a [[synchronous orbit]], which strongly suggested that the bulge effect was real and not spurious. Any final doubts were erased when Pluto and Charon entered a five-year period of mutual eclipses between 1985 and 1990. This occurs when the Pluto-Charon [[Orbital plane (astronomy)|orbital plane]] is edge-on as seen from Earth, which only happens at two intervals in Pluto's 248-year orbital period. It was fortuitous that one of these intervals happened to occur so soon after Charon's discovery. Images showing Pluto and Charon resolved into separate disks were taken for the first time by the [[Hubble Space Telescope]] in the 1990s. Later, the development of [[adaptive optics]] made it possible to also resolve Pluto and Charon into separate disks using ground-based telescopes. ==Name== Charon was originally known by the temporary designation '''S/1978 P 1''', according to the then recently instituted convention. On [[June 24]], [[1978]], Christy first suggested the name ''Charon'' as a scientific-sounding version of his wife Charlene's nickname, "Char." Although colleagues at the [[United States Naval Observatory|Naval Observatory]] proposed ''[[Persephone]],'' Christy stuck with ''Charon'' after discovering it coincidentally refers to a Greek mythological figure.<ref>Govert Shillling, "A Bump in the Night" in ''[[Sky & Telescope]]'' (June 2008) pp. 26-27. Prior to this, Christy had considered naming the moon ''[[Land of Oz|Oz]]''.</ref> Official adoption of the name by the [[International Astronomical Union|IAU]] would wait until late [[1985]], and was announced on [[3 January]] [[1986]].<ref>{{cite web | title = IAU Circular No. 4157 | date = [[January 3]] [[1986]] | url = http://cfa-www.harvard.edu/iauc/04100/04157.html | accessdate = 2007-04-10 }}</ref> In Greek mythology, [[Charon (mythology)|Charon]] is the ferryman of the dead, a figure with close ties to the god Hades, which the Romans identified with their god Pluto. Although in English the mythological figure ''Charon'' is pronounced with a hard ''k'' sound, Christy pronounced the ''ch'' in the moon's name as ''sh'' (IPA {{IPA|[ʃ]}}), after his wife Charlene. The ''sh'' pronunciation is customary among astronomers when speaking English.{{Fact|date=December 2007}} Speakers of languages other than English, which use the name ''Charon,'' follow the pronunciation established for the mythological figure. ==Physical characteristics== [[Image:Charon 2.jpg|300px|thumb|left|Artist's concept of Charon seen from the surface of Pluto.]] Charon's diameter is about [[1 E6 m|1,207]] [[kilometre|km]] (750 miles), just over half that of Pluto, with a surface area of [[1 E12 m²|4,580,000]] [[Square kilometre|km²]]. Unlike Pluto, which is covered with [[nitrogen]] and [[methane]] ices, the Charonian surface appears to be dominated by less [[volatile]] water ice, and also appears to have no atmosphere. In 2007, observations by the [[Gemini Observatory]] of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers.<ref name=ice>{{cite web|title=Charon: An ice machine in the ultimate deep freeze|work=Gemini Observatory|year=2007|url=http://www.spaceflightnow.com/news/n0707/17charon/|accessdate=2007-07-18}}</ref> Mutual eclipses of Pluto and Charon in the 1980s allowed astronomers to take spectra of Pluto and then the combined spectrum of the pair. By subtracting Pluto's spectrum from the total, astronomers were able to spectroscopically determine the surface composition of Charon. Charon's volume and mass allow us to calculate its density; from this we can tell Charon is largely an icy body and contains less rock by proportion than its partner Pluto, supporting the idea Charon was created by a giant impact into Pluto's icy mantle (see Formation below.) There are two conflicting theories about Charon's internal structure: some scientists believe it to be a differentiated body like Pluto with a rocky core and an icy mantle while others believe Charon to be of uniform composition throughout. Evidence in support of the former position was found in 2007, when observations by the [[Gemini Observatory]] of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers. The fact that the ice was still in crystalline form suggested it had been recently deposited, as solar radiation would have degraded older ice to an amorphous state after 30,000 years or so.<ref name=ice/> ==Orbital characteristics== [[Image:Plutoncharon1.jpg|300px|right|thumbnail|Surface of Pluto and Charon, as determined from brightness variations during mutual occultations.]] Charon and Pluto revolve about each other every 6.387 days. The two objects are [[tidal locking|gravitationally locked]], so each keeps the same face towards the other. The average distance between Charon and Pluto is 19,570 km (12,163 mi). The discovery of Charon allowed astronomers to accurately calculate the mass of the Plutonian system, and mutual [[occultation]]s revealed their sizes. However, neither indicated the two bodies' individual masses, which could only be estimated, until the discovery of Pluto's outer moons in late 2005. Details in the orbits of the outer moons reveal that Charon has approximately 11.65% of the mass of Pluto.<ref name="Buie06"/> This shows it to have a density of 1.65±0.06 g/cm³, suggesting a composition of 55±5% "rock" to 45% ice, whereas Pluto is somewhat denser and about 70% "rock". ==Formation== Simulation work published in [[2005]] by Robin Canup suggested that Charon could have formed by a [[giant impact hypothesis|giant impact]] around 4.5 [[1000000000 (number)|billion]] years ago, much like the [[Earth]] and [[Moon]]. In this model a large [[Kuiper belt]] object struck Pluto at high velocity, destroying itself and blasting off much of Pluto's outer [[mantle (geology)|mantle]], and Charon coalesced from the debris. However, such an impact should result in an icier Charon and rockier Pluto than what scientists have found. It is now thought that Pluto and Charon may have been two bodies that collided before going into orbit about each other. The collision would have been violent enough to boil off volatile ices like methane but not violent enough to have destroyed either body.<ref>{{cite journal| url=http://sciencenow.sciencemag.org/cgi/content/full/2006/105/2| title=Charon's Shadow Illuminates Its True Nature| last=Schriber| journal=ScienceNOW| year=2005}}</ref> ==Moon or dwarf planet?== [[Image:Pluto system 2006.jpg|thumb|right|225px|Pluto and its three known moons.]] The [[centre of mass#Barycenter|center of mass]] (barycenter) of the Pluto-Charon system lies outside either body. Since neither object truly rotates around the other, and Charon has 11.6% the mass of Pluto, it has been argued that Charon should not be considered to be a satellite of Pluto. Instead, it has been suggested that they form dual dwarf planets, following the re-classification of Pluto. In a draft proposal for the [[2006 redefinition of planet|2006 redefinition]] of the term, the [[International Astronomical Union]] proposed that a planet be defined as a body that orbits the sun that is large enough for gravitational forces to render the object (nearly) spherical. Under this proposal, Charon would have been classified as a planet, since the draft explicitly defined a planetary satellite as one in which the barycenter lies within the major body. In the final definition, Pluto was reclassified as a [[dwarf planet]], but the formal definition of a planetary satellite was not decided upon, leaving Charon's status unclear. (Charon is not in the list of dwarf planets currently recognized by the IAU.) The moons [[Nix (moon)|Nix]] and [[Hydra (moon)|Hydra]] also orbit the same barycenter, but are not large enough to be spherical, and are simply considered to be satellites of Pluto (or, under the alternative viewpoint, of the Pluto-Charon system).<ref name=NixHydra>{{cite web |last=Stern |first=Alan |date=2005-05-15 |url=http://www.boulder.swri.edu/plutomoons/ |title=Background Information Regarding Our Two Newly Discovered Satellites of Pluto |publisher=Planetary Science Directorate (Boulder Office) |accessdate=2006-08-30}}</ref> ==References== {{reflist}} ==External links== {{commons|Pluto}} * [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Plu_Charon Charon Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration] * [[James W. Christy]] and [[Robert Sutton Harrington|Robert S. Harrington]], "The satellite of Pluto," [http://adsabs.harvard.edu//full/seri/AJ.../0083//0001005.000.html ''The Astronomical Journal'' '''83''' (1978) 1005] * [[Marc W. Buie]], [http://www.boulder.swri.edu/~buie/pluto/chphases.html Phases of Charon as seen from Pluto], [[Lowell Observatory]] * [http://news.bbc.co.uk/2/hi/science/nature/4230918.stm Hubble reveals new map of Pluto], [[BBC]] News, [[12 September]] [[2005]] * IAU Circular No. 3241<ref>{{cite web|url = http://cfa-www.harvard.edu/iauc/03200/03241.html |title = IAUC 3241: 1978 P 1; 1978 (532) 1; 1977n |accessdate = 2008-06-22}}</ref> describing the discovery * Measuring the Size of a Small, Frost World ([[ESO]] press release January 2006)<ref>{{cite web|url = http://www.eso.org/outreach/press-rel/pr-2006/pr-02-06.html |title = ESO - 2006 |accessdate = 2008-06-22}}</ref> * [http://arxiv.org/abs/astro-ph/0602082 M. J. Person et al.: Charon’s Radius and Density from the Combined Data Sets of the 2005 July 11 Occultation] (submitted to the [[Astronomical Journal]], [[3 February]] [[2006]]) <br />{{Moons of dwarf planets}} {{Solar System moons (compact)}} {{Trans-Neptunian objects}} {{Trans-Neptunian dwarf planets}} {{Solar System}} <!--Categories--> [[Category:Pluto's moons]] <!--Other languages--> [[ar:شرن]] [[zh-min-nan:Charon (oē-chheⁿ)]] [[be-x-old:Харон (карлікавая плянэта)]] [[br:C'haron (loarenn)]] [[bg:Харон (планета-джудже)]] [[ca:Caront (satèl·lit)]] [[cs:Charon (měsíc)]] [[co:Caronte (astrunumia)]] [[cy:Charon (lloeren)]] [[da:Charon (måne)]] [[de:Charon (Mond)]] [[et:Charon (kaaslane)]] [[es:Caronte (luna)]] [[eo:Karono (luno)]] [[fr:Charon (lune)]] [[ga:Carón]] [[gv:Charon (fo-phlannad)]] [[gl:Caronte (satélite)]] [[ko:카론 (위성)]] [[hr:Haron (mjesec)]] [[id:Charon (bulan)]] [[it:Caronte (astronomia)]] [[he:כארון (ירח)]] [[pam:Charon]] [[ka:ქარონი]] [[kw:Charon]] [[la:Charon (satelles)]] [[lt:Charonas (palydovas)]] [[hu:Charon (hold)]] [[nl:Charon (maan)]] [[ja:カロン (衛星)]] [[no:Charon (måne)]] [[nn:Plutomånen Charon]] [[nds:Charon (Maand)]] [[pl:Charon (księżyc)]] [[pt:Caronte (satélite)]] [[ro:Charon (satelit)]] [[ru:Харон (спутник)]] [[simple:Charon (moon)]] [[sk:Cháron (mesiac)]] [[sl:Haron (luna)]] [[sr:Харон]] [[fi:Kharon]] [[sv:Charon (måne)]] [[th:คารอน]] [[tr:Charon (uydu)]] [[uk:Харон (супутник)]] [[zh:冥卫一]]