Charon

Charon's Pluto-facing hemisphere (determined from brightness variations during Pluto-Charon occultations)
Discovery
Discovered by	James W. Christy
Discovery date	June 22, 1978
Orbital characteristics [1]
Epoch 2,452,600.5
Semi-major axis	19,571 ± 4 km
Eccentricity	0.00000 ± 0.00007
Orbital period	6.3872304 ± 0.0000011 d (6 d 9 h 17 m 36.7 ± 0.1 s)
Inclination	0° (to Pluto's equator) 119.591 ± 0.014° (to Pluto's orbit) 112.783 ± 0.014° (to the ecliptic)
Longitude of ascending node	223.046 ± 0.014° (to vernal equinox)
Satellite of	Pluto
Physical characteristics
Mean radius	603.5 ± 1.5 km[2] (0.095 Earths)
Surface area	4.58×106 km²
Mass	(1.52 ± 0.06)×1021 kg[1] (2.54×10−4 Earths) (11.6% of Pluto)
Mean density	1.65 ± 0.06 g/cm³[1]
Equatorial surface gravity	0.278 m/s2
Escape velocity	0.580 km/s .36 mi/s
Rotation period	synchronous
Axial tilt	zero?
Albedo	varies between 0.36 and 0.39
Temperature	-220°C (53 K)
Apparent magnitude	16.8[3]
Absolute magnitude	1[4]
Angular diameter	55 milli-arcsec[5]
Adjectives	Charonian

Charon (pronounced /ˈʃɛərən/ SHAIR-ən, or /ˈkɛərən/ KAIR-ən as in Greek: Χάρων), discovered in 1978, is either the largest moon of Pluto or one member of a 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 and Hydra), Charon is now also referred to as Pluto I. The New Horizons mission is scheduled to visit Charon and Pluto in July 2015. Image File history File links No higher resolution available. ... James Walter Christy (born 1938) is an American astronomer. ... is the 173rd day of the year (174th in leap years) in the Gregorian calendar. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... For the science fiction novella by William Shunn, see Inclination (novella). ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... The Longitude of the ascending node (☊, also noted Ω) is one of the orbital elements used to specify the orbit of an object in space. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. ... For other uses, see Pluto (disambiguation). ... In mathematics, a spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... To help compare sizes of different areas, here is a list of areas between 10 million km² and 100 million km². See also areas of other orders of magnitude. ... Square kilometre (U.S. spelling: square kilometer), symbol km², is a decimal multiple of SI unit of surface area square metre, one of the SI derived units. ... For other uses, see Mass (disambiguation). ... Kg redirects here. ... For other uses, see Density (disambiguation). ... BIC pen cap, about 1 gram. ... A cubic centimetre (cm3) is an SI derived unit of volume, equal to the volume of a cube with side length of 1 centimetre. ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... For other senses of this term, see escape velocity (disambiguation). ... kilometre per second is an SI derived unit of both speed (scalar) and velocity (vector), signified by the symbol km/s or km s-1. ... In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis relative to the background stars. ... Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... For other uses, see Albedo (disambiguation). ... For other uses, see Temperature (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... For other uses, see Pluto (disambiguation). ... Pluto and Charon are sometimes informally considered to be a double (dwarf) planet. ... Artists impression of Pluto (background) and Charon (foreground). ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Nix (formerly known as S/2005 P 2), is a natural satellite of Pluto. ... Hydra (formerly known as S/2005 P 1) is a natural satellite of Pluto. ... For other uses, see New Horizons (disambiguation). ...

Charon should not be confused with the similarly named Chiron, a smaller object in the outer solar system. 2060 Chiron (IPA: ) is an object in the outer solar system with an orbit between those of Saturn and Uranus and a radius of 71±5 km [1]. Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a comet. ...

[edit] Discovery

Charon was discovered by astronomer James Christy on June 22, 1978, when he was examining highly magnified images of Pluto on photographic plates 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. James Walter Christy (born 1938) is an American astronomer. ... is the 173rd day of the year (174th in leap years) in the Gregorian calendar. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... For other uses, see Pluto (disambiguation). ... Photographic plates were one of the earliest forms of photographic film, in which a light-sensitive emulsion of silver salts was applied to a glass plate. ... is the 119th day of the year (120th in leap years) in the Gregorian calendar. ... Year 1965 (MCMLXV) was a common year starting on Friday (link will display full calendar) of the 1965 Gregorian calendar. ...

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. In astronomy, a light curve is a graph of light intensity as a function of time. ... A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. ...

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 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. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. ...

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. The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... A deformable mirror can be used to correct wavefront errors in an astronomical telescope. ...

[edit] 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 Naval Observatory proposed Persephone, Christy stuck with Charon after discovering it coincidentally refers to a Greek mythological figure.^[6] Official adoption of the name by the IAU would wait until late 1985, and was announced on 3 January 1986.^[7] is the 175th day of the year (176th in leap years) in the Gregorian calendar. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ... This article is about the Greek goddess. ... IAU redirects here. ... This article is about the year. ... is the 3rd day of the year in the Gregorian calendar. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ...

In Greek 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 [ʃ]), after his wife Charlene. The sh pronunciation is customary among astronomers when speaking English.^{[citation needed]} Speakers of languages other than English, which use the name Charon, follow the pronunciation established for the mythological figure. Michelangelos rendition of Charon. ...

[edit] Physical characteristics

Artist's concept of Charon seen from the surface of Pluto.

Charon's diameter is about 1,207 km (750 miles), just over half that of Pluto, with a surface area of 4,580,000 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.^[8] Image File history File links Charon_2. ... Image File history File links Charon_2. ... To help compare different orders of magnitude this page lists lengths between 106 and 107 m (1,000 and 10,000 km). ... “km” redirects here. ... To help compare orders of magnitude of different surface areas  here is a list of areas between 1 million km² and 10 million km². See also areas of other orders of magnitude. ... Square kilometre (U.S. spelling: square kilometer), symbol km², is a decimal multiple of SI unit of surface area square metre, one of the SI derived units. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Methane is a chemical compound with the molecular formula . ... Look up volatile in Wiktionary, the free dictionary. ... The Gemini Observatory is an astronomical observatory consisting of two 8-metre telescopes at different sites. ...

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.^[8] The Gemini Observatory is an astronomical observatory consisting of two 8-metre telescopes at different sites. ...

[edit] Orbital characteristics

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 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 occultations 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.^[1] 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". Image File history File links Plutoncharon1. ... Image File history File links Plutoncharon1. ... Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ... In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ...

[edit] Formation

Simulation work published in 2005 by Robin Canup suggested that Charon could have formed by a giant impact around 4.5 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, 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.^[9] Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... The Big Splash redirects here. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... This article is about Earth as a planet. ... This article is about Earths moon. ... The Kuiper belt, derived from data from the Minor Planet Center. ... Earth cutaway from core to exosphere. ...

[edit] Moon or dwarf planet?

Pluto and its three known moons.

The 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. Image File history File linksMetadata Download high-resolution version (1085x1095, 118 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solar System Pluto User:Wahkeenah Plutos natural satellites Talk:Plutos natural satellites User:Appraiser User:JohnnyBGood... Image File history File linksMetadata Download high-resolution version (1085x1095, 118 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solar System Pluto User:Wahkeenah Plutos natural satellites Talk:Plutos natural satellites User:Appraiser User:JohnnyBGood... The center of mass or center of inertia of an object is a point at which the objects mass can be assumed, for many purposes, to be concentrated. ...

In a draft proposal for the 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 final definition left the solar system with eight planets, pictured above (not to scale) Displays the remaining eight planets with the celestial bodies that have now been designated as dwarf planets. ... IAU redirects here. ... Artists impression of Pluto (background) and Charon (foreground). ...

The moons Nix and 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).^[10] Nix (formerly known as S/2005 P 2), is a natural satellite of Pluto. ... Hydra (formerly known as S/2005 P 1) is a natural satellite of Pluto. ...

[edit] References

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 292nd day of the year (293rd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 164th day of the year (165th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 292nd day of the year (293rd in leap years) in the Gregorian calendar. ... Sky & Telescope is a monthly magazine providing articles and information on all aspects of astronomy, space exploration, telescope equipment, and amateur telescope making and use. ... Oz is a fairy country (fantasy region) containing four lands under the rule of one monarch. ... is the 3rd day of the year in the Gregorian calendar. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 100th day of the year (101st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 199th day of the year (200th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 135th day of the year (136th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 242nd day of the year (243rd in leap years) in the Gregorian calendar. ...

[edit] External links

Wikimedia Commons has media related to:

Pluto

• Charon Profile by NASA's Solar System Exploration
• James W. Christy and Robert S. Harrington, "The satellite of Pluto," The Astronomical Journal 83 (1978) 1005
• Marc W. Buie, Phases of Charon as seen from Pluto, Lowell Observatory
• Hubble reveals new map of Pluto, BBC News, 12 September 2005
• IAU Circular No. 3241^[1] describing the discovery
• Measuring the Size of a Small, Frost World (ESO press release January 2006)^[2]
• 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)

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