Charon (moon)

Charon, also known as (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km. It was discovered in 1978 at the United States Naval Observatory 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.

The reddish-brown cap of the north pole of Charon is composed of tholins; organic macromolecules that may be essential ingredients of life. These tholins were produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over 19,000 km (12,000 mi) to the orbiting moon.[10]

The New Horizons spacecraft is the only probe that has visited the Pluto system. It approached Charon to within 27,000 km (17,000 mi) in 2015.

Charon in True Color - High-Res
Charon in true color, imaged by New Horizons
Discovered byJames W. Christy
Discovery date22 June 1978
Pronunciation/ˈʃærən/ SHARR-ən or /ˈkɛərən/ KAIR-ən[note 1]
Named after
Discoverer's wife, Charlene and Charon
(134340) Pluto I[1]
Orbital characteristics [3]
Epoch 2452600.5
(2002 Nov 22)
Periapsis17,536 km
Apoapsis17,536 km
19591 km[2]
6.3872304±0.0000011 d
(6 d, 9 h, 17 m, 36.7 ± 0.1 s)
0.21 km/s[note 2]
Inclination0.080° (to Pluto's equator)[2]
119.591°±0.014° (to Pluto's orbit)
112.783°±0.014° (to the ecliptic)
223.046°±0.014° (to vernal equinox)
Satellite ofPluto
Physical characteristics
Mean radius
606.0±0.5 km[4][5] (0.095 Earths, 0.51 Plutos)
Flattening<0.5% [6]
4.6×106 km2 (0.0090 Earths)
Volume(9.32±0.14)×108 km3 (0.00086 Earths)
Mass(1.586±0.015)×1021 kg[4][5]
(2.66×10−4 Earths)
(12.2% of Pluto)
Mean density
1.702±0.017 g/cm3[5]
0.288 m/s2
0.59 km/s
0.37 mi/s
Albedo0.2 to 0.5 at a solar phase angle of 15°
Temperature−220 °C (53 K)
55 milli-arcsec[9]


Charon Discovery
Charon's discovery at the Naval Observatory Flagstaff Station as a time-varying bulge on the image of Pluto (seen near the top at left, but absent on the right). Negative image.
Mosaic of best-resolution images of Charon from different angles

Charon was discovered by United States Naval Observatory astronomer James Christy, using the 1.55-meter (61 in) telescope at United States Naval Observatory Flagstaff Station (NOFS),[11] On June 22, 1978, he had been examining highly magnified images of Pluto on photographic plates 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.[12] The International Astronomical Union formally announced Christy's discovery to the world on July 7, 1978.[13]

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 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.


Lytovchenko Olexandr Kharon
Charon is named after Charon, the ferryman of the dead in Greek mythology,[14] shown in this nineteenth-century painting by Alexander Litovchenko

Author Edmond Hamilton referred to three moons of Pluto in his 1940 science fiction novel Calling Captain Future, naming them Charon, Styx, and Cerberus.[15]

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".[14][16] Although colleagues at the Naval Observatory proposed Persephone, Christy stuck with Charon after discovering that it coincidentally refers to a Greek mythological figure:[14] Charon (/ˈkɛərɒn/ or /ˈkɛərən/; Greek Χάρων) is the ferryman of the dead, closely associated in myth with the god Hades, whom the Romans identified with their god Pluto. The IAU officially adopted the name in late 1985 and it was announced on January 3, 1986.[17]

There is minor debate over the preferred pronunciation of the name. The practice of following the classical pronunciation established for the mythological ferryman Charon (IPA [ˈkɛ:rən]) is used by major English-language dictionaries, such as the Merriam-Webster and Oxford English Dictionary.[18][19] These indicate only one pronunciation of "Charon" when referring specifically to Pluto's moon: with an initial "k" sound. Speakers of many languages other than English, and many English-speaking astronomers as well, follow this pronunciation.[20]

However, Christy himself pronounced the ch as sh (IPA [ʃ]), after his wife Charlene. Because of this, as an acknowledgement of Christy and sometimes as an in-joke or shibboleth, the initial sh pronunciation is common among astronomers when speaking English,[note 3][20][21][22] and this is the prescribed pronunciation at NASA and of the New Horizons team.[23][note 4]


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 and the 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.[24] 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 (CH
) 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.[4]


Animation of moons of Pluto - Front view
Front view
Animation of moons of Pluto - Side view
Side view
Pluto-Charon system-new
A simulated view of the Pluto–Charon system showing that Pluto orbits a point outside itself. Also visible is the mutual tidal locking between the two bodies.

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 19,570 kilometres (12,160 mi). The discovery of Charon allowed astronomers to calculate accurately 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 revealed that Charon has approximately 12% of the mass of Pluto.[3]

Physical characteristics

Charon, Earth & Moon size comparison
Size comparisons: Earth, the Moon, and Charon

Charon's diameter is 1,212 kilometres (753 mi), just over half that of Pluto,[4][5] and larger than the dwarf planet Ceres, and the twelfth largest natural satellite in the Solar System. Charon is sufficiently massive to have collapsed into a spheroid under its own gravity. Charon's slow rotation means that there is almost no flattening. Its equatorial and polar radii differ by less than 1%.[4]


The two conflicting theories about Charon's internal structure

Charon's volume and mass allow calculation of its density, 1.702±0.017 g/cm3,[5] 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.[25] 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 state after roughly thirty thousand years.[26]


Charon in enhanced color to bring out differences in surface composition.

Unlike Pluto's surface, which is composed of nitrogen and methane ices, Charon's surface appears to be dominated by the less volatile water ice. 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 cryogeysers and cryovolcanoes.[26][27]

Photometric mapping of Charon's surface shows a latitudinal trend in albedo, with a bright equatorial band and darker poles. The north polar region is dominated by a very large dark area informally dubbed "Mordor" by the New Horizons team.[28][29][30] The favored explanation for this phenomenon is that they are 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.[31] In addition to Mordor, New Horizons found evidence of extensive past geology that suggests that Charon is probably differentiated;[29] 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.[32]

In 2018,the International Astronomical Union named one crater on Charon, as Revati who is a character in the Hindu epic Mahabharata.[33][34]

Charon has a series of extensive grabens or canyons, such as Serenity Chasma, which extend as an equatorial belt for at least 1000 km. Argo Chasma potentially reaches as deep as 9 km, with steep cliffs that may rival Verona Rupes on Miranda for the title of tallest cliff in the solar system.[35]

Organa, the youngest crater of Charon.

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 49,000 miles (79,000 km).[36][37]

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 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 circles (3). The image was taken by Hubble's Faint Object Camera (FOC) when the system was 2.6 billion miles (4.4 billion kilometers) away from Earth[38] Later, the development of adaptive optics made it possible to resolve Pluto and Charon into separate disks using ground-based telescopes.[16]

In June 2015, the New Horizons 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 were guests at the Johns Hopkins Applied Physics Laboratory during the New Horizons closest approach.

Charon Discovery
(1) Discovery;
(2) HST – before correction;
Pluto and Charon from Hubble
(3) HST – after correction;
First Color Animated Images show Pluto and its Moon Charon
(4) 1st color animated view;


The center of mass (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 system with Pluto. The International Astronomical Union (IAU) states that Charon is considered to be just a satellite of Pluto, but the idea that Charon might be classified a dwarf planet in its own right may be considered at a later date.[39]

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, 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.[39] Had the draft proposal been accepted, even the Moon would be classified as a planet in billions of years when the tidal acceleration 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.[40]

The other moons of Pluto, Nix, Hydra, Kerberos and Styx, 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).[41]


Cpmap cyl PS717 HR 180

Global map of Charon


Identically processed enhanced-color views of Pluto and Charon

PIA19967 - Charon in Detail

High resolution enhanced-color mosaic of Charon

Pluto charon 150709 color final

Pluto and Charon, to scale. Viewed by New Horizons on approach.


Pluto and Charon as viewed by New Horizons
(color; July 11, 2015).


Pluto and Charon as viewed by New Horizons
(false-color; July 13, 2015).


Charon – night-side as viewed by New Horizons
(July 17, 2015).


Charon – Flyover video animation (00:20)
(released October 1, 2015).

See also


  1. ^ The former is the discoverer's original pronunciation. The latter per the anglicized pronunciation of the Greek: Χάρων.
  2. ^ Calculated on the basis of other parameters.
  3. ^ Astronomer Mike Brown can be heard pronouncing it [ˈʃɛɹɪn] in ordinary conversation on the KCET interview ["Julia Sweeney and Michael E. Brown". Hammer Conversations: KCET podcast. 2007. Archived from the original on 2008-10-06. Retrieved 2008-10-01.] at 42min 48sec. Being a long-time resident of California, he does not distinguish the /ær/ vowel of the name Sharon and the /ɛər/ vowel of the classical pronunciation of Charon.
  4. ^ Hal Weaver, who led the team that discovered Nix and Hydra, also pronounces it [ˈʃɛɹɪn] (/ˈʃærən/ with a generic American accent) on the Discovery Science Channel documentary Passport to Pluto, premiered 2006-01-15.


  1. ^ Jennifer Blue (2009-11-09). "Gazetteer of Planetary Nomenclature". IAU Working Group for Planetary System Nomenclature (WGPSN). Retrieved 2010-02-24.
  2. ^ a b c "Planetary Satellite Mean Orbital Parameters — Satellites of Pluto". Solar System Dynamics. NASA's Jet Propulsion Laboratory. 2013-08-23. Retrieved 2017-12-27.
  3. ^ a b Buie, Marc W.; Grundy, William M.; Young, Eliot F.; Young, Leslie A.; Stern, S. Alan (5 Jun 2006). "Orbits and Photometry of Pluto's Satellites: Charon, S/2005 P1, and S/2005 P2". The Astronomical Journal. 132 (1): 290–298. arXiv:astro-ph/0512491. Bibcode:2006AJ....132..290B. doi:10.1086/504422.
  4. ^ a b c d e Stern, S.A.; Bagenal, F.; Ennico, K.; Gladstone, G.R.; Grundy, W.M.; McKinnon, W.B.; Moore, J.M.; Olkin, C.B.; Spencer, J.R. (16 Oct 2015). "The Pluto system: Initial results from its exploration by New Horizons". Science. 350 (6258): aad1815. arXiv:1510.07704. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913.
  5. ^ a b c d e Stern, S.A.; Grundy, W.; McKinnon, W.B.; Weaver, H.A.; Young, L.A. (15 Dec 2017). "The Pluto System After New Horizons". arXiv:1712.05669 [astro-ph.EP].
  6. ^ Nimmo, F.; Umurhan, O.; Lisse, C.M.; Bierson, C.J.; Lauer, T.R.; Buie, M.W.; Throop, H.B.; Kammer, J.A.; Roberts, J.H.; McKinnon, W.B.; Zangari, A.M.; Moore, J.M.; Stern, S.A.; Young, L.A.; Weaver, H.A.; Olkin, C.B.; Ennico, K.; and the New Horizons GGI team (1 May 2017). "Mean radius and shape of Pluto and Charon from New Horizons images". Icarus. 287: 12–29. arXiv:1603.00821. Bibcode:2017Icar..287...12N. doi:10.1016/j.icarus.2016.06.027.
  7. ^ "Classic Satellites of the Solar System". Observatorio ARVAL. April 15, 2007. Archived from the original on 2010-07-31. Retrieved 2007-10-19.
  8. ^ David Jewitt (June 2008). "The 1000 km Scale KBOs". Institute for Astronomy (UH). Retrieved 2008-06-13.
  9. ^ "Measuring the Size of a Small, Frost World" (Press release). European Southern Observatory. 2006-01-04. Archived from the original on 2006-01-18. Retrieved 2007-10-19.
  10. ^ Bromwich, Jonah Engel; St. Fleur, Nicholas (14 September 2016). "Why Pluto's Moon Charon Wears a Red Cap". The New York Times. Retrieved 2016-09-14.
  11. ^ "Charon Discovery Image". Solar System Exploration. NASA's Jet Propulsion Laboratory. 16 December 2003. Archived from the original on 2013-05-02. Retrieved 2013-07-10.
  12. ^ Dick, Steven J. (2013). "The Pluto Affair". Discovery and Classification in Astronomy: Controversy and Consensus. Cambridge University Press. pp. 15–17. ISBN 978-1-107-03361-0.
  13. ^ "IAUC 3241: 1978 P 1; 1978 (532) 1; 1977n". Central Bureau for Astronomical Telegrams. July 7, 1978. Retrieved 2011-07-05.
  14. ^ a b c Shilling, Govert (June 2008). "A Bump in the Night". Sky & Telescope. pp. 26–27. Prior to this, Christy had considered naming the moon Oz.
  15. ^ Codex Regius (2016). Pluto & Charon. CreateSpace Independent Publishing Platform. ISBN 978-1534960749.
  16. ^ a b Williams, Matt (14 Jul 2015). "Charon: Pluto's Largest Moon". Universe Today. Retrieved 2015-10-08.
  17. ^ "IAUC 4157: CH Cyg; R Aqr; Sats OF SATURN AND PLUTO". Central Bureau for Astronomical Telegrams. January 3, 1986. Retrieved 2011-07-05.
  18. ^ "Charon".
  19. ^ "Charon". Oxford English Dictionary.
  20. ^ a b Pronounced "KAIR en" or "SHAHR en" per "Pluto Facts". Nine Planets. Retrieved 2008-10-03.
  21. ^ Pronounced 'with a soft "sh" ' per "Welcome to the solar system, Nix and Hydra!". The Planetary Society Weblog. Archived from the original on 2009-02-10. Retrieved 2008-10-03.
  22. ^ US Naval Observatory spokesman Jeff Chester, when interviewed on the NPR commentary "Letters: Radiology Dangers, AIDS, Charon". Morning Edition. 2006-01-19. Retrieved 2008-10-03. (at 2min 49sec), says Christy pronounced it [ˈʃɛɹɒn] rather than classical [ˈkɛɹɒn]. In normal conversation, the second vowel is reduced to a schwa: /ˈkɛərən/ in RP (ref: OED).
  23. ^ Pronounced "Sharon" /ˈʃærən/ per "NASA New Horizons: The PI's Perspective—Two for the Price of One". Retrieved 2008-10-03. and per "New Horizons Team Names Science Ops Center After Charon's Discoverer". Retrieved 2008-10-03.
  24. ^ Canup, Robin (January 28, 2005). "A Giant Impact Origin of Pluto–Charon". Science. 307 (5709): 546–50. Bibcode:2005Sci...307..546C. doi:10.1126/science.1106818. PMID 15681378.
  25. ^ "Charon". Retrieved 2015-10-08.
  26. ^ a b "Charon: An ice machine in the ultimate deep freeze". Gemini Observatory. 2007. Retrieved 2007-07-18.
  27. ^ Cook; Desch, Steven J.; Roush, Ted L.; Trujillo, Chadwick A.; Geballe, T. R. (2007). "Near-Infrared Spectroscopy of Charon: Possible Evidence for Cryovolcanism on Kuiper Belt Objects". The Astrophysical Journal. 663 (2): 1406–1419. Bibcode:2007ApJ...663.1406C. doi:10.1086/518222.
  28. ^ "The New Horizons team refers to a dark patch on Pluto's moon as 'Mordor'". The Week. Retrieved 2015-07-15.
  29. ^ a b "New Horizons Photos Show Pluto's Ice Mountains and Charon's Huge Crater". NBC News. Retrieved 2015-07-15.
  30. ^ Corum, Jonathan (15 July 2015). "New Horizons Reveals Ice Mountains on Pluto". The New York Times. Retrieved 2015-07-15.
  31. ^ Howett, Carley (11 September 2015). "New Horizons probes the mystery of Charon's red pole". Retrieved 2015-09-16.
  32. ^ Beatty, Kelly (2 October 2015). "Charon: Cracked, Cratered, and Colorful". Sky and Telescope. Retrieved 2015-10-03.
  33. ^
  34. ^ "Hindus welcome naming crater on Pluto's largest moon Charon after Revati - News Patrolling". Dailyhunt.
  35. ^ Keeter, Bill (2016-06-23). "A 'Super Grand Canyon' on Pluto's Moon Charon". NASA. Retrieved 2017-08-03.
  36. ^ "Pluto's Big Moon Charon Has a Bizarre Mountain in a Moat (Photo)". Retrieved 2015-10-08.
  37. ^ "Mysterious Mountain Revealed in First Close-up of Pluto's Moon Charon". Universe Today. Retrieved 2015-10-08.
  38. ^ "Pluto and Charon". Hubble Space Telescope. 16 May 1994. Retrieved 2015-10-08.
  39. ^ a b "Pluto and the Developing Landscape of Our Solar System". IAU. Retrieved 2013-07-10.
  40. ^ Robert Roy Britt (2006-08-18). "Earth's moon could become a planet". CNN Science & Space. Retrieved 2009-11-25.
  41. ^ Stern, Alan; Weaver, Hal; Mutchler, Max; Steffl, Andrew; Merline, Bill; Buie, Marc; Spencer, John; Young, Eliot; Young, Leslie (2005-05-15). "Background Information Regarding Our Two Newly Discovered Satellites of Pluto". Planetary Science Directorate. Southwest Research Institute, Boulder Office. Retrieved 2006-08-30.

External links

2016 in science

A number of significant scientific events occurred in 2016. The United Nations declared 2016 the International Year of Pulses.

Bio of a Space Tyrant

Bio of a Space Tyrant series is a six-book science-fiction series by Piers Anthony based within the Solar System. The series revolves around the character Hope Hubris and his family, and charts Hope's ascent from poor Hispanic refugee to Tyrant of Jupiter, a single person heading the Executive, Judicial and Legislative branches of the government. It is considerably more adult-themed than many of Anthony's earlier works.

The novels are set in a future several hundred years distant at a point where the nations of Earth have expanded into and filled the Solar System. Various planets, moons and asteroids within the Solar System have political, religious and geographical affiliations similar to those on 1980s Earth. Many events in the series parallel modern-day situations; for instance, Mars is controlled by the countries formerly comprising the Middle East, and has the largest supply of iron, the primary fuel in Anthony's universe. Ganymede parallels Cuba, and has a Communist government allied with North Saturn's, which corresponds to the Soviet Union. A "Missile Crisis" is an event in the series; many other such correspondences abound.

The series is presented as Hope's first-person autobiography, and includes his image as a tyrant and womanizer. It is clear from the introductions and epilogues that Hope died before his memoir's publication and that his career as military man, politician, executive and statesman was greatly misunderstood by the public, especially his various affairs with women, a major focus of the series.

Charon (disambiguation)

Charon, in Greek mythology, is the ferryman who carried the souls of the dead to the underworld.

Charon may also refer to:

Charon (moon), a moon of the dwarf planet Pluto

Discovery and exploration of the Solar System

Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.

The Solar System — our Sun’s system of planets, moons, and smaller debris — is humankind’s cosmic backyard. Small by factors of millions compared to interstellar distances,

the spaces between the planets are daunting, but technologically surmountable

Geology of Charon

The geology of Charon are the characteristics of the surface, crust, and interior of Pluto's moon Charon. Charon's diameter is 1,208 km (751 mi)—just over half that of Pluto. Charon is sufficiently massive to have collapsed into a spheroid under its own gravity.

James W. Christy

James Walter "Jim" Christy (born September 15, 1938) is an American astronomer.

Christy was born in 1938 in Milwaukee, Wisconsin. He attended the University of Arizona and earned a Bachelor of Science degree in astronomy from there in 1965. On June 22, 1978 while working at the United States Naval Observatory, he discovered that Pluto had a moon, which he named Charon shortly afterwards. The name remained unofficial until its adoption by the IAU in 1986.The discovery was made by carefully examining an enlargement of a photographic plate of Pluto and noticing it had a very slight bulge on one side. This plate and others had been marked "poor" because the elongated image of Pluto was thought to be a defect resulting from improper alignment. The 1965 plates included a note "Pluto image elongated", but observatory astronomers, including Christy, assumed that the plates were defective until 1978.However, Christy noticed that only Pluto was elongated—the background stars were not. His earlier work at the Naval Observatory had included photographing double stars, so it occurred to him that this bulge might be a companion of Pluto. After examining images from observatory archives dating back to 1965, he concluded that the bulge was indeed a moon.The photographic evidence was considered convincing but not conclusive (it remained possible that the bulge was due to Pluto having an unexpectedly irregular shape). However, based on Charon's calculated orbit, a series of mutual eclipses of Pluto and Charon was predicted and observed, confirming the discovery.

In more modern telescopes, such as the Hubble or ground-based telescopes using adaptive optics, separate images of Pluto and Charon can be resolved, and the New Horizons probe took images showing some of Charon's surface features.

In late 2008, the asteroid 129564 Christy was named in his honor.† As of 2015, he resides in Flagstaff, Arizona. He has been married to Charlene Mary since 1975 and has four children. On July 14, 2015, he and Clyde Tombaugh's children were guests at the Johns Hopkins Applied Physics Laboratory when the New Horizons spacecraft successfully performed the first flyby of the Pluto-Charon system.

Christy's inspiration for the name "Charon" came about due to a personal interest in naming the moon after his wife. He used her nickname, "Char" for Charlene, and added -on (for his interest in physics in protons and electrons, which have -on endings) to make Charon. It was only later that he found the same name in mythology, that being the ferryman who carried souls across the Acheron River, one of the five mythical rivers that surrounded Pluto's underworld.

List of New Horizons topics

List of New Horizons topics is a list of topics related to the New Horizons spacecraft, an unmanned space probe launched 2006 to Pluto and beyond.

On January 19, 2006 it was launched directly into a solar-escape trajectory at 16.26 kilometers per second (58,536 km/h; 36,373 mph) from Cape Canaveral using an Atlas V version with 5 SRBs and Star 48B thirdstage . New Horizons passed the Moon's orbit in just nine hours.

132524 APL, Distant observation target

15810 Arawn (1994 JR1), Distant observation target

2011 HM102, Neptune Trojan considered as an observation target

2011 KW48, distant observation target

2014 MT69, former candidate for New Horizons flyby.

2014 OS393, former potential flyby target

2014 PN70, former potential flyby target

(486958) 2014 MU69, flyby on New Year's day 2019

Alice (spacecraft instrument), one of seven major instruments on New Horizons

Alice Bowman, New Horizons staff

AJ-60A, solid rocket booster of which five were used in the New Horizons launch.

Atlas V, New Horizons launch vehicle

Cape Canaveral Air Force Station Space Launch Complex 41, launch site

Centaur (rocket stage), New Horizons upper stage

Charon (moon), Pluto's big moon

Common Core Booster, part of New Horizons first stage launcher

Clyde Tombaugh, discovered Pluto in 1930 from Lowell Observatory

Kirk (crater)

Kuiper belt, region from about 30-60 AU New Horizons explores

Lisa Hardaway, New Horizons staff

Long Range Reconnaissance Imager, one of seven major instruments on New Horizons

GPHS-RTG, electrical and thermal heat source of New Horizons

Interplanetary dust cloud

Interplanetary medium, studied during Hibernation

Mongoose-V, CPU in New Horizons

NASA Deep Space Network, for New Horizons Earth radio communications

Nasreddin (crater)

New Frontiers program, NASA parent program of New Horizons

New Horizons 2, design study for twin

Organa (crater)

Pluto, primary target of New Horizons

Pluto Energetic Particle Spectrometer Science Investigation, one of seven major instruments on New Horizons

Ralph, one of seven major instruments on New Horizons

REX, one of seven major instruments on New Horizons

Daniel Sarokon, NASA employee honored at New Horizons launch

Star 48B, New Horizons 3rd stage

Alan Stern, New Horizons staff

SWAP, one of seven major instruments on New Horizons

Tvashtar Paterae

Vader (crater), crater observed by New Horizons

Venetia Burney Student Dust Counter, one of seven major instruments on New Horizons

Venetia Burney, New Horizons instrument honorific, Burney proposed Pluto's name in 1930

List of largest craters in the Solar System

Following are the largest impact craters on various worlds of the Solar System. For a full list, see List of craters in the Solar System.

Natural satellite

A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet (or sometimes another small Solar System body).

In the Solar System there are six planetary satellite systems containing 185 known natural satellites. Four IAU-listed dwarf planets are also known to have natural satellites: Pluto, Haumea, Makemake, and Eris. As of September 2018, there are 334 other minor planets known to have moons.The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System (although there are minor-planet systems with even greater ratios, notably the Pluto–Charon system). At 3,474 km (2,158 miles) across, the Moon is 0.27 times the diameter of Earth.

Persephone (disambiguation)

Persephone is a Greek goddess. See also Proserpina, her Roman equivalent, and Proserpina (disambiguation).

Persephone may also refer to:

Persephone Books, an independent publisher of mostly women's writing in London

The Persephone, a salvage ship in The Beachcombers

Abbreviation, Psph.

Planetary flyby

A planetary flyby is the act of sending a space probe past a planet or a dwarf planet close enough to record scientific data. This is a subset of the overall concept of a flyby in spaceflight.

Flybys commonly use gravity assists to "slingshot" a space probe on its journey to its primary objective, but may themselves be used as primary means.

The first flyby of another planet with a functioning spacecraft took place on December 14, 1962, when Mariner 2 zoomed by the planet Venus.New Horizons performed flyby maneuvers of Jupiter, Pluto and its moons in the 21st century. This type of maneuver allowed it to reach Pluto at high velocity without the complications of slowing down, after which it proceeded into the Kuiper belt on a solar system escape trajectory.

For comparison, New Horizons reached Jupiter in just over year (launched in January 2006) it flewby in February 2007. In contrast, Galileo spacecraft took about six years (launched 1989, arrive at Jupiter 1995) and when it got there it had expend fuel to slow down to enter orbit, and was overall much heavier. The atmospheric entry probe did not slow down but required an advanced entry shield and the atmosphere of Jupiter to slow down. (See also Aerobraking)

There also an even closer version of flyby, a sort of fly in where the spacecraft actually enters and passes through a bodies atmosphere, called a Aerogravity assist. This could be compared to the natural phenomenon of Earth-grazing fireball

Solar System

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, at least four of the dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy.

dwarf planets
Likely dwarf
Minor-planet moons
Ranked by size
TNO classes
Dwarf planets (moons)
Asteroid belt
Centaurs (extended)
Other resonances/
unknown resonances:
Scattered disc
Area uncertain
Detached objects

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