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Ganymede (moon)
From Wikipedia, the free encyclopedia
 Click image for description |
|
| Discovery | |
|---|---|
| Discovered by: | G. Galilei S. Marius |
| Discovery date: | January 11, 1610 |
| Orbital characteristics | |
| Periapsis: | 1,069,200 km (0.007147 AU) |
| Apoapsis | 1,071,600 km (0.007163 AU) |
| Mean radius of orbit: | 1,070,400 km (0.007155 AU) |
| Eccentricity: | 0.002[1] |
| Orbital period: | 7.15455296 d (0.019588 a) |
| Avg. orbital speed: | 10.880 km/s |
| Inclination: | 2.21° (to the ecliptic) 0.20° to Jupiter's equator) |
| Satellite of: | Jupiter |
| Physical characteristics | |
| Mean radius: | 2631.2 km (0.413 Earths) |
| Surface area: | 87.0 million km² (0.171 Earths) [2] |
| Volume: | 7.6×1010 km³ (0.0704 Earths) |
| Mass: | 1.4819×1023 kg (0.025 Earths) |
| Mean density: | 1.942 g/cm³ |
| Equatorial surface gravity: | 1.428 m/s2 (0.146 g) |
| Escape velocity: | 2.741 km/s (6,130 mph) |
| Rotation period: | synchronous |
| Axial tilt: | zero |
| Albedo: | 0.43 ± 0.02[3] |
| Temperature: | ~109 K (−172°C) |
| Apparent magnitude: | 4.61 (opposition) [3] |
| Atmosphere | |
| Surface pressure: | trace |
| Composition: | oxygen |
Ganymede (pronounced /ˈgænɨmiːd/, Greek Γανυμήδης) is Jupiter's largest natural satellite, and the largest natural satellite in the Solar System; it is larger in diameter than Mercury but has only about half its mass. Ganymede is one of four planetary satellites of Jupiter that could be seen with the naked eye under favorable conditions, if not for the brighter light of nearby Jupiter. Other than possibly the other Galilean Satellites, the only planetary satellite visible with the naked eye is our own Moon.
Ganymede's discovery is generally credited to Galileo Galilei who documented its existence in 1610.[4] The name Ganymede was suggested soon after by Simon Marius, for the cup-bearer of the Greek gods, beloved of Zeus (see Ganymede).[5] This name and the names of the other Galilean satellites fell into disfavor for a considerable time, and were not revived in common use until the mid-20th century. In much of the earlier astronomical literature, it is simply referred to by its Roman numeral designation (a system introduced by Galileo) as Jupiter III or as the "third satellite of Jupiter". Ganymede is the only Galilean moon of Jupiter named after a male figure.
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On January 7, 1610, Galileo Galilei observed three stars near Jupiter.[6] The next night, he saw that the stars had moved.[6] A fourth star, Ganymede, was found on January 11.[6] By January 15, Galileo came to the conclusion that the stars were bodies orbiting Jupiter.[6]
Galileo claimed the right to name the moons. He chose between “Cosmic Stars” and “Medicean Stars”. The second was chosen.[7]
Nicholas Clade Fabri de Peiresc tried to give the moons individual names, but his system was not used.[7] Simon Marius, who had originally claimed to have found the Galilean Satellites,[8] tried to name the moons the Saturn of Jupiter, the Jupiter of Jupiter (this was Ganymede), the Venus of Jupiter, and the Mercury of Jupiter, a system which never caught on.[7] From a suggestion by Johannes Kepler, Simon Marius once again tried to name the moons.[7]
| “ | …Then there was Ganymede, the handsome son of King Tros, whom Jupiter, having taken the form of an eagle, transported to heaven on his back, as poets fabulously tell… the Third, on account of its majesty of light, Ganymede…[6] | ” |
However, none of these various naming schemes caught on, except to use a numerical system. Following the discovery of moons of Saturn, a naming system based on the one Kepler and Marius had created was put to use for Jupiter’s moons.[7]
Ganymede orbits at a distance of 1,070,400 kilometers, making it the third farthest out of the Galilean satellites.[9] Ganymede revolves around Jupiter in seven days and three hours. Like most moons, Ganymede is tidally locked, meaning it keeps one face always pointing toward Jupiter. This is because its revolution around Jupiter is the same as its rotation.[10]
Ganymede participates in an orbital resonance with Europa and Io, in which for every orbit of Ganymede, Europa orbits twice and Io orbits four times.[11] The resonance causes an orbital eccentricity of 0.002.[1][11] Also due to the orbital resonance as well as Jupiter, tidal heating is present. Tidal heating doesn’t have as much of an effect on Ganymede as it does on Europa and Io, but there are still outcomes of the heating. For example, Ganymede’s interior has differentiated.[11]
Ganymede is composed of 49 to 59% silicate rock, and its density is consistent with a high proportion of water ice. Indications from the Galileo orbiter data suggest that Ganymede is differentiated into a three-layer structure: a silicate core, a mantle composed of mixed ice and rock, and a crust of refrozen ice. The core is predicted to be made of "Prinn-Fegley" assemblage rock, which is rock predicted to be condensed from a proto-Jovian nebula, or the anhydrous PTC assemblage. CI carbonaceous chondrite is plausible as a lower mantle constituent. The three aforementioned types of rock have densities of 2.766, 3.262, and 3.756 g/cm3 respectively.[12]
The Ganymedean surface is a mix of two types of terrain: very old, highly cratered dark regions and somewhat younger (but still ancient) lighter regions marked with an extensive array of grooves and ridges. Their origin is clearly of a tectonic nature, probably formed by the extension, stretching, and faulting of the icy crust. The dark terrain contains clays and organic materials that could indicate the composition of the impactors from which Jovian satellites accreted.[13]
Extensive cratering is seen on both types of terrain. The density of cratering indicates an age of 4 billion years for the dark terrain, similar to the highlands of the Moon, and a somewhat younger age for the bright grooved terrain (but how much younger is uncertain). Craters both overlay and are cross-cut by the groove systems indicating that some of the grooves are quite ancient. Relatively young craters with rays of ejecta are also visible.[14] Unlike on the Moon, however, Ganymedean craters are quite flat, lacking the ring mountains and central depressions common to craters on the Moon and Mercury. This is probably due to the relatively weak nature of Ganymede's icy crust which can flow and thereby soften the relief. Ancient craters whose relief has disappeared leaving only a "ghost" of a crater are known as palimpsests.
The largest feature on Ganymede is a dark plain named Galileo Regio, as well as a series of concentric grooves, or furrows, that are remnants of an ancient impact crater long since obscured by subsequent geological activity.
In 1972, a team of Indian, British and American astronomers working at Indonesia's Bosscha Observatory in Lembang detected a thin atmosphere around Ganymede during an occultation when Jupiter (and Ganymede) passed in front of a star.[15] Evidence for a tenuous oxygen atmosphere on Ganymede, very similar to the one found on Europa, has since been found by the Hubble Space Telescope.[16] Note that this is not necessarily evidence of life: it is thought that the oxygen is produced when water ice on Ganymede's surface is split into hydrogen and oxygen by radiation and then the hydrogen is lost due to its low atomic mass.
The Galileo orbiter's first flyby of Ganymede discovered that Ganymede has its own magnetic field, embedded inside Jupiter's huge field. Ganymede is the only moon known to have a magnetosphere.[16] Ganymede's intrinsic magnetic field is probably generated in a similar fashion to the Earth's: as a result of conducting material moving in the interior, likely originating in its metallic core. Ganymede also has an induced magnetic field component, indicating that the satellite contains a subsurface layer that acts as a conductor. It is thought that this conductive material is a layer of liquid water containing salt, located at about 150 km depth and sandwiched between layers of different density forms of ice.
Ganymede is the most largely concentrated, solid body known in the solar system, which suggests complete global differentiation and a metallic core. The magnetic field detected around Ganymede is assumed to be caused by thermal or compositional convection in the core, if the magnetic field is the product of dynamo action or magnetoconvection. Convection within the silicate mantle is also a possibility during Ganymede's history.[18]
It has been suggested that Ganymede may be amenable to life, due to experiments in which bacteria have survived intense pressure.[19] However, scientists say that the chances of life existing on Europa are much higher than on Ganymede, because Europa's ocean is closer to the surface than Ganymede's.[20]
- List of craters on Ganymede
- Lunar and Planetary Institute
- Colonization of Ganymede
- Jupiter's moons in fiction
- ^ a b Ganymede: Facts and Figures. Solar System Exploration. Retrieved on 2007-12-07.
- ^ Using the mean radius
- ^ a b Yeomans, Donald K. (2006-Jul-13). Planetary Satellite Physical Parameters. JPL Solar System Dynamics. Retrieved on 2007-11-05.
- ^ Galilei, G.; Sidereus Nuncius (March 13, 1610)
- ^ Marius, S.; (1614); Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici, where he attributes the suggestion to Johannes Kepler
- ^ a b c d e The Discovery of the Galilean Satellites. Views of the Solar System. Retrieved on 2007-11-24.
- ^ a b c d e Satellites of Jupiter. The Galileo Project. Retrieved on 2007-11-24.
- ^ DISCOVERY. Cascadia Community College. Retrieved on 2007-11-24.
- ^ Jupiter's Moons. The Planetary Society. Retrieved on 2007-12-07.
- ^ Miller, Ron; William K. Hartmann (May 2005). The Grand Tour: A Traveler's Guide to the Solar System, 3rd edition, Thailand: Workman Publishing, 108. ISBN 0-7611-3547-2.
- ^ a b c High Tide on Europa. SPACE.com. Retrieved on 2007-12-07.
- ^ Ganymede & Callisto2. es.ucl.ac.uk. Retrieved on October 20, 2007.
- ^ Lunar and Planetary Institute (2001). THE GRANDEUR OF GANYMEDE: SUGGESTED GOALS FOR AN ORBITER MISSION..
- ^ Lunar and Planetary Institute (1997). Ganymede.
- ^ R. W. Carlson et al., An Atmosphere on Ganymede from Its Occultation of SAO 186800 on 7 June 1972,Science 5 October 1973: Vol. 182. no. 4107, pp. 53 - 55
- ^ a b nineplanets.org (October 31, 1997). Ganymede page.
- ^ http://spaceflightnow.com/news/n0012/29ganyflyby/
- ^ INTERNAL STRUCTURE AND MECHANISMS OF CORE CONVECTION ON GANYMEDE. es.ucl.ac.uk. Retrieved on October 20, 2007.
- ^ Experiment shows bacteria survive intense pressure. cbc.ca. Retrieved on October 21, 2007.
- ^ Bridges, A.; Ocean Lurks Deep in Ganymede, Galileo Finds, Space.com (18 December 2000)
- Ganymede Profile by NASA's Solar System Exploration
- Ganymede page on The
Nine8 Planets - Jupiter's Moon Ganymede on Views of the Solar System
- Ganymede Crater Database Lunar and Planetary Institute
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|
|
|---|---|
| Listed in increasing distance from Jupiter. Temporary names in italics. | |
| Amalthea group | Metis · Adrastea · Amalthea · Thebe |
| Galilean moons | Io · Europa · Ganymede · Callisto |
| Themisto | |
| Himalia group | Leda · Himalia · Lysithea · Elara · S/2000 J 11 |
| Carpo · S/2003 J 12 | |
| Ananke group | Ananke · Praxidike · Harpalyke · Iocaste · Euanthe · Thyone (core) Euporie · S/2003 J 3 · S/2003 J 18 · Thelxinoe · Helike · Orthosie · S/2003 J 16 · Hermippe · Mneme · S/2003 J 15 (peripheral) |
| Carme group | S/2003 J 17 · S/2003 J 10 · Pasithee · Chaldene · Arche · Isonoe · Erinome · Kale · Aitne · Taygete · S/2003 J 9 · Carme · S/2003 J 5 · S/2003 J 19 · Kalyke · Eukelade · Kallichore |
| Pasiphaë group | Eurydome · S/2003 J 23 · Hegemone · Pasiphaë · Sponde · Cyllene · Megaclite · S/2003 J 4 · Callirrhoe · Sinope · Autonoe · Aoede · Kore |
| S/2003 J 2 | |
| Rings of Jupiter | |
|
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||
|---|---|---|
| Major Moons | Io · Europa · Ganymede · Callisto |  |
| Characteristics | Cloud pattern on Jupiter · Great Red Spot · Jupiter's magnetosphere · Oval BA · Rings of Jupiter · Moons | |
| Exploration | Pioneer program · Voyager program · Galileo (spacecraft) · Juno (spacecraft) · Europa Orbiter | |
| Other | Jupiter-crosser asteroid · Earthly Branches · Colonization · Jupiter mass | |
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|---|---|---|
| Planetary satellites | Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian |  |
| Other satellite systems | Plutonian · Eridian · Asteroid satellites | |
| Largest satellites | Ganymede · Titan · Callisto · Io · Moon · Europa · Triton Titania · Rhea · Oberon · Iapetus · Charon · Umbriel · Ariel · Dione · Tethys · Enceladus · Miranda · Proteus · Mimas |
|
| Inner satellites • Trojans • Irregulars • List • List by diameter • Timeline of discovery • Naming | ||
| The Solar System |
|---|
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| The Sun · Mercury · Venus · Earth · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Eris |
| Planets · Dwarf planets · Moons: Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian |
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| See also astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Solar System Portal |