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Charon ( or ), known as (134340) Pluto I, is the largest of the five known natural satellites of the
dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. It has a mean radius of . Charon is the sixth-largest known
trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au). Typically ...
after Pluto, Eris, Haumea, Makemake and Gonggong. It was discovered in 1978 at the
United States Naval Observatory United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depo ...
in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS). With half the diameter and one eighth the mass of Pluto, Charon is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Plutonian system lies outside Pluto, and the two bodies are tidally locked to each other. The reddish-brown cap of the north pole of Charon is composed of tholins,
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
macromolecule A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...
s that may be essential ingredients of
life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy ...
. These tholins were produced from
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and related gases which may have been released by cryovolcanic eruptions on the moon, or may have been transferred over from the
atmosphere of Pluto The atmosphere of Pluto is the tenuous layer of gases surrounding Pluto. It consists mainly of nitrogen (N2), with minor amounts of methane (CH4) and carbon monoxide (CO), all of which are vaporized from their ices on Pluto's surface. It contain ...
to the orbiting moon. The ''
New Horizons ''New Horizons'' is an interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a ...
'' spacecraft is the only probe that has visited the Pluto system. It approached Charon to within in 2015.


Discovery

Charon was discovered by United States Naval Observatory astronomer James Christy, using the telescope at United States Naval Observatory Flagstaff Station (NOFS). On June 22, 1978, he had been examining highly magnified images of
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
on
photographic plate Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...
s taken with the telescope two months prior. Christy noticed that a slight elongation appeared periodically. The bulge was confirmed on plates dating back to April 29, 1965. The
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
formally announced Christy's discovery to the world on July 7, 1978. 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. This resulted in reassessments of Pluto's size, mass, and other physical characteristics because the calculated mass and
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
of the Pluto–Charon system had previously been attributed to Pluto alone. Doubts about Charon's existence were erased when it and Pluto entered a five-year period of mutual eclipses and transits 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 soon after Charon's discovery.


Name

After its discovery, 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 In ancient Greek mythology and religion, Persephone ( ; gr, Περσεφόνη, Persephónē), also called Kore or Cora ( ; gr, Κόρη, Kórē, the maiden), is the daughter of Zeus and Demeter. She became the queen of the underworld aft ...
'', Christy stuck with ''Charon'' after discovering that it coincidentally refers to a Greek mythological figure: Prior to this, Christy had considered naming the moon '' Oz''.
Charon In Greek mythology, Charon or Kharon (; grc, Χάρων) is a psychopomp, the ferryman of Hades, the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the ...
(; grc, Χάρων) is the ferryman of the dead, closely associated in myth with the god
Hades Hades (; grc-gre, ᾍδης, Háidēs; ), in the ancient Greek religion and myth, is the god of the dead and the king of the underworld, with which his name became synonymous. Hades was the eldest son of Cronus and Rhea, although this also ...
or Plouton ( grc, Πλούτων, ), whom the Romans identified with their god
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. The IAU officially adopted the name in late 1985 and it was announced on January 3, 1986. Coincidentally, nearly four decades before Charon's discovery, science fiction author Edmond Hamilton referred to three moons of Pluto named Charon, Styx, and Cerberus in his 1940 novel ''Calling Captain Future''. There is minor debate over the preferred pronunciation of the name. The mythological figure is pronounced with a sound, and this is often followed for the moon as well. However, Christy himself pronounced the initial as a sound, as he had named the moon after his wife Charlene. Many English-speaking astronomers follow the classical convention, but others follow Christy's,Astronomer Mike Brown can be heard pronouncing it in ordinary conversation on the KCET interview [] at 42min 48sec.Pronounced "KAIR en" or "SHAHR en" per and that is the prescribed pronunciation at NASA and of the ''New Horizons'' team.Pronounced "Sharon" per and per Hal Weaver, who led the team that discovered Nix and Hydra, also pronounces it ( with a generic American accent) on the Discovery Science Channel documentary ''Passport to Pluto'', premiered 2006-01-15.


Formation

Simulation work published in 2005 by Robin Canup suggested that Charon could have been formed by a collision around 4.5 billion years ago, much like
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
and the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. In this model, a large
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 tim ...
object struck Pluto at high velocity, destroying itself and blasting off much of Pluto's outer
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
, and Charon coalesced from the debris. However, such an impact should result in an icier Charon and rockier Pluto than scientists have found. It is now thought that Pluto and Charon might 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 Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
() but not violent enough to have destroyed either body. The very similar density of Pluto and Charon implies that the parent bodies were not fully differentiated when the impact occurred.


Atmosphere

Charon has no significant atmosphere. There has been speculation about a minuscule atmosphere surrounding the moon, but there has been no indication of anything substantial. Pluto does have a thin but significant atmosphere, and under some conditions Charon's gravitation pulls some of Pluto's upper atmosphere, specifically nitrogen, from Pluto's ice formations, toward Charon's surface. The nitrogen is mostly caught in the combined center of gravity between the two bodies before reaching Charon, but any gas that does reach Charon is held closely against the surface. The gas is mostly made up of ions of nitrogen, but the amounts are negligible compared to the total of Pluto's atmosphere. The many spectral signatures of ice formations on the surface of Charon have led some to believe that the ice formations could supply an atmosphere, but atmosphere supplying formations have not been confirmed yet. Many scientists theorize that these ice formations could be concealed out of direct sight, either in deep craters or beneath Charon's surface. Similar to how Pluto transfers atmosphere to Charon, Charon's relatively low gravity, due to its low mass, causes any atmosphere that might be present to rapidly escape the surface into space. Even through stellar occultation, which is used to probe the atmosphere of stellar bodies, scientists cannot confirm an existing atmosphere; this was tested in 1986 while attempting to perform stellar occultation testing on Pluto. Charon also acts as a protector for Pluto's atmosphere, blocking the solar wind that would normally collide with Pluto, damaging its atmosphere. Since Charon blocks these solar winds, its own atmosphere is diminished, instead of Pluto's. This effect is also a serious potential explanation for Charon's lack of atmosphere; when it begins to accumulate, the solar winds shut it down. Although, it is still possible for Charon to have an atmosphere. As previously stated, Pluto transfers some of its atmospheric gas to Charon, from where it tends to escape into space. Assuming Charon's density is 1.71 g/cm3, which is the rough estimate we currently have, it would have a surface gravity of 0.6 of Pluto's. It also has a higher mean molecular weight than Pluto and a lower exobase surface temperature, so that the gases in its atmosphere would not escape as rapidly from Charon as they do from Pluto. There has been significant proof of CO2 gas and H2O vapor on the surface of Charon, but these vapors are not sufficient for a viable atmosphere due to their low vapor pressures. Pluto's surface has abundant ice formations, but these are volatile, as they are made up of volatile substances like methane. These volatile ice structures cause a good deal of geological activity, keeping its atmosphere constant, while Charon's ice structures are mainly made up of water and carbon dioxide, much less volatile substances that can stay dormant and not affect the atmosphere much.


Orbit

Charon and Pluto orbit each other every 6.387 days. The two objects are gravitationally locked to one another, so each keeps the same face towards the other. This is a case of mutual tidal locking, as compared to that of the Earth and the Moon, where the Moon always shows the same face to Earth, but not vice versa. The average distance between Charon and Pluto is . The discovery of Charon allowed astronomers to calculate accurately the mass of the Plutonian system, and mutual
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
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 revealed that Charon has approximately 12% of the mass of Pluto.


Physical characteristics

Charon's diameter is , just over half that of Pluto. Larger than the dwarf planet Ceres, it is the twelfth-largest
natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
in the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
. Charon is even similar in size to
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
's moons Umbriel and Ariel. Charon's slow rotation means that there should be little flattening or tidal distortion, if Charon is sufficiently massive to be in
hydrostatic equilibrium In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planeta ...
. Any deviation from a perfect sphere is too small to have been detected by observations by the ''New Horizons'' mission. This is in contrast to
Iapetus In Greek mythology, Iapetus (; ; grc, Ἰαπετός, Iapetós), also Japetus, is a Titan, the son of Uranus and Gaia and father of Atlas (mythology), Atlas, Prometheus, Epimetheus (mythology), Epimetheus, and Menoetius (mythology), Menoetius. ...
, a Saturnian moon similar in size to Charon but with a pronounced
oblate In Christianity (especially in the Roman Catholic, Orthodox, Anglican and Methodist traditions), an oblate is a person who is specifically dedicated to God or to God's service. Oblates are individuals, either laypersons or clergy, normally liv ...
ness dating to early in its history. The lack of such oblateness in Charon could mean that it is currently in hydrostatic equilibrium, or simply that its orbit approached its current one early in its history, when it was still warm. Based on mass updates from observations made by ''New Horizons'' the mass ratio of Charon to Pluto is 0.1218:1. This is much larger than the Moon to the Earth: 0.0123:1. Because of the high mass ratio, the barycenter is outside of the radius of Pluto, and the Pluto–Charon system has been referred to as a dwarf double planet. With four smaller satellites in orbit about the two larger worlds, the Pluto–Charon system has been considered in studies of the orbital stability of
circumbinary planet A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circum ...
s.


Interior

Charon's volume and mass allow calculation of its density, , from which it can be determined that Charon is slightly less dense than Pluto and suggesting a composition of 55% rock to 45% ice (± 5%), whereas Pluto is about 70% rock. The difference is considerably lower than that of most suspected collisional satellites. Before ''New Horizons flyby, there were two conflicting theories about Charon's internal structure: some scientists thought Charon to be a differentiated body like Pluto, with a rocky core and an icy mantle, whereas others thought it would be uniform 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 cryogeysers. The fact that the ice was still in crystalline form suggested it had been deposited recently, because solar radiation would have degraded it to an
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...
state after roughly thirty thousand years.


Surface

Unlike Pluto's surface, which is composed of
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
ices, Charon's surface appears to be dominated by the less volatile water ice. In 2007, observations by the
Gemini Observatory The Gemini Observatory is an astronomical observatory consisting of two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. The twin Gemini telescopes prov ...
of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active
cryogeysers A geyser (, ) is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only i ...
and cryovolcanoes. Photometric mapping of Charon's surface shows a latitudinal trend in
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
, with a bright equatorial band and darker poles. The north polar region is dominated by a very large dark area informally dubbed "
Mordor In J. R. R. Tolkien's fictional world of Middle-earth, Mordor (pronounced ; from Sindarin ''Black Land'' and Quenya ''Land of Shadow'') is the realm and base of the evil Sauron. It lay to the east of Gondor and the great river Anduin, an ...
" by the ''New Horizons'' team. The favored explanation for this feature is that it is formed by condensation of gases that escaped from Pluto's atmosphere. In winter, the temperature is −258 °C, and these gases, which include nitrogen, carbon monoxide, and methane, condense into their solid forms; when these ices are subjected to solar radiation, they chemically react to form various reddish tholins. Later, when the area is again heated by the Sun as Charon's seasons change, the temperature at the pole rises to −213 °C, resulting in the volatiles sublimating and escaping Charon, leaving only the tholins behind. Over millions of years, the residual tholin builds up thick layers, obscuring the icy crust. In addition to Mordor, ''New Horizons'' found evidence of extensive past geology that suggests that Charon is probably differentiated; in particular, the southern hemisphere has fewer craters than the northern and is considerably less rugged, suggesting that a massive resurfacing event—perhaps prompted by the partial or complete freezing of an internal ocean—occurred at some point in the past and removed many of the earlier craters. In 2018, the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
named one crater on Charon, as Revati who is a character in the Hindu epic
Mahabharata The ''Mahābhārata'' ( ; sa, महाभारतम्, ', ) is one of the two major Sanskrit epics of ancient India in Hinduism, the other being the '' Rāmāyaṇa''. It narrates the struggle between two groups of cousins in the K ...
. Charon has a series of extensive
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...
s or canyons, such as
Serenity Chasma Serenity Chasma is the unofficial name given to a large pull-apart fault on Pluto's moon, Charon. It is part of a series of faults that run along the perimeter of Vulcan Planum. It was discovered by the ''New Horizons'' mission, and informally ...
, which extend as an equatorial belt for at least . Argo Chasma potentially reaches as deep as , with steep cliffs that may rival
Verona Rupes Verona Rupes is a cliff on Miranda, a moon of Uranus. It was discovered by the ''Voyager 2'' space probe in January 1986. The cliff face, previously thought to be from high, as of 2016 is estimated to be high, which makes it the tallest known ...
on Miranda for the title of tallest cliff in the solar system.


Mountain in a moat

In a released photo by ''New Horizons'', an unusual surface feature has captivated and baffled the scientist team of the mission. The image reveals a mountain rising out of a depression. It's "a large mountain sitting in a moat", said Jeff Moore, of NASA's Ames Research Center, in a statement. "This is a feature that has geologists stunned and stumped", he added. ''New Horizons'' captured the photo from a distance of .


Observation and exploration

Since the first blurred images of the moon (1), images showing Pluto and Charon resolved into separate disks were taken for the first time by the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
in the 1990s (2). The telescope was responsible for the best, yet low quality images of the moon. In 1994, the clearest picture of the Pluto–Charon system showed two distinct and well defined disks (3). The image was taken by Hubble's Faint Object Camera (FOC) when the system was 4.4 billion kilometers (2.6 billion miles) away from Earth Later, the development of
adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...
made it possible to resolve Pluto and Charon into separate disks using ground-based telescopes. In June 2015, the ''
New Horizons ''New Horizons'' is an interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a ...
'' spacecraft captured consecutive images of the Pluto–Charon system as it approached it. The images were put together in an animation. It was the best image of Charon to that date (4). In July 2015, the ''New Horizons'' spacecraft made its closest approach to the Pluto system. It is the only spacecraft to date to have visited and studied Charon. Charon's discoverer James Christy and the children of
Clyde Tombaugh Clyde William Tombaugh (February 4, 1906 January 17, 1997) was an American astronomer. He discovered Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper belt. At the time of discovery, Pluto was cons ...
were guests at the Johns Hopkins Applied Physics Laboratory during the New Horizons closest approach.


Classification

The
center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
(barycenter) of the Pluto–Charon system lies outside either body. Because neither object truly orbits the other, and Charon has 12.2% the mass of Pluto, it has been argued that Charon should be considered to be part of a
binary planet In astronomy, a double planet (also binary planet) is a binary satellite system where both objects are planets, or planetary-mass objects, that share an orbital axis external to both planetary bodies. Although up to a third of the star syst ...
with Pluto. The
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU) states that Charon is considered to be just a satellite of Pluto, but the idea that Charon might be classified as a dwarf planet in its own right may be considered at a later date. In a draft proposal for the 2006 redefinition of the term, the IAU 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, because 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 A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
, but the formal definition of a planetary satellite was not decided upon. Charon is not in the list of dwarf planets currently recognized by the IAU. Had the draft proposal been accepted, even the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
would hypothetically be classified as a planet in billions of years when the
tidal acceleration Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon) and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit away f ...
that is gradually moving the Moon away from Earth takes it far enough away that the center of mass of the system no longer lies within Earth. The other moons of Pluto
Nix Nix or NIX may refer to: Places * Nix, Alabama, an unincorporated community, United States * Nix, Texas, a ghost town in southwestern Lampasas County, Texas, United States * Nix (moon), a moon of Pluto People * Nix (surname), listing people wit ...
, Hydra, Kerberos and
Styx In Greek mythology, Styx (; grc, Στύξ ) is a river that forms the boundary between Earth (Gaia) and the Underworld. The rivers Acheron, Cocytus, Lethe, Phlegethon, and Styx all converge at the centre of the underworld on a great marsh, ...
orbit the same barycenter but they are not large enough to be spherical and they are simply considered to be satellites of Pluto (or of Pluto–Charon).


Gallery


Videos


See also

* List of natural satellites


Notes


References


External links


Charon Profile
a
NASA's Solar System Exploration site
*
Hubble reveals new map of Pluto
BBC News, September 12, 2005 *
Cryovolcanism on Charon and other Kuiper Belt Objects

''New Horizons'' Camera Spots Pluto’s Largest Moon – July 10, 2013



40th anniversary NASA video
describing the discovery and naming of Charon (June 22, 2018) * NASA CG
video
of Charon flyover (July 14, 2017)
CGI video
simulation of rotating Charon by Seán Doran (se
album
for more)
Google Charon 3D
interactive map of the moon *
Interactive 3D gravity simulation of Pluto and Charon in addition to Pluto's four other moons Styx, Kerberos, Hydra and Nix
{{Authority control Moons of Pluto Trans-Neptunian satellites Articles containing video clips M Planetary-mass satellites Moons with a prograde orbit