Ganymede (moon)

Ganymede
Ganymede in true color as imaged by the Juno spacecraft in June 2021[a][1]
Discovery[2][3]
Discovered byGalileo Galilei
Simon Marius
Discovery dateJanuary 7, 1610
Designations
Pronunciation/ˈɡænɪmiːd/
GAN-im-eed[4]
Named after
Γανυμήδης, Ganymēdēs
Alternative names
Jupiter III
AdjectivesGanymedian,[5]
Ganymedean[6][7] (/ˌɡænəˈmiːdi.ən/)
Orbital characteristics
Periapsis1069200 km[b]
Apoapsis1071600 km[c]
1070400 km[8]
Eccentricity0.0013[8]
7.15455296 d[8]
Average orbital speed
10.880 km/s
Inclination2.214° (to the ecliptic)
0.20° (to Jupiter's equator)[8]
Satellite ofJupiter
GroupGalilean moon
Physical characteristics
Mean radius
2634.1±0.3 km (0.413 Earths)[9]
8.72×107 km2 (0.171 Earths)[d]
Volume7.66×1010 km3 (0.0704 Earths)[e]
Mass1.4819×1023 kg (0.025 Earths)[9]
Mean density
1.936 g/cm3 (0.351 Earths)[9]
Surface gravity
1.428 m/s2 (0.146 g)[f]
Moment of inertia factor
0.3115±0.0028[10]
2.741 km/s[g]
Synodic rotation period
synchronous
0–0.33°[11] (to Jupiter's equator)
North pole right ascension
268.20°[12]
North pole declination
64.57°[12]
Albedo0.43±0.02[13]
Surface temp. min mean max
K 70[14] 110[14] 152[15]
°C −203 −163 −121
4.61 (opposition)[13]
4.38 (in 1951)[16]
Angular diameter
1.2 to 1.8 arcseconds
Atmosphere
Surface pressure
0.2–1.2 μPa (1.97×10−12–1.18×10−11 atm)[17]
Composition by volumemostly oxygen[17]

Ganymede is a natural satellite of Jupiter and the largest and most massive in the Solar System. Like Saturn's largest moon Titan, it is larger than the planet Mercury, but has somewhat less surface gravity than Mercury, Io, or the Moon due to its lower density compared to the three.[18] Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.

Ganymede is composed of silicate rock and water in approximately equal proportions. It is a fully differentiated body with an iron-rich, liquid metallic core, giving it the lowest moment of inertia factor of any solid body in the Solar System. Its internal ocean potentially contains more water than all of Earth's oceans combined.[19][20][21][22]

Ganymede's magnetic field is probably created by convection within its core, and influenced by tidal forces from Jupiter's far greater magnetic field.[23] Ganymede has a thin oxygen atmosphere that includes O, O
2, and possibly O
3.[17] Atomic hydrogen is a minor atmospheric constituent. Whether Ganymede has an ionosphere associated with its atmosphere is unresolved.[24]

Ganymede's surface is composed of two main types of terrain, the first of which are lighter regions, generally crosscut by extensive grooves and ridges, dating from slightly less than 4 billion years ago, covering two-thirds of Ganymede. The cause of the light terrain's disrupted geology is not fully known, but may be the result of tectonic activity due to tidal heating. The second terrain type are darker regions saturated with impact craters, which are dated to four billion years ago.[9]

Ganymede's discovery is credited to Simon Marius and Galileo Galilei, who both observed it in 1610,[2][h] as the third of the Galilean moons, the first group of objects discovered orbiting another planet.[26] Marius soon named it after Ganymede, a Trojan prince desired by Zeus, who carried him off to serve as cupbearer to the gods.[27]

Beginning with Pioneer 10, several spacecraft have explored Ganymede.[28] The Voyager probes, Voyager 1 and Voyager 2, refined measurements of its size, while Galileo discovered its underground ocean and magnetic field. The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moons Explorer (JUICE), which was launched in 2023.[29] After flybys of all three icy Galilean moons, it is planned to enter orbit around Ganymede.[30]


Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).

  1. ^ "'Tros Crater, Ganymede – PJ34-1 Detail' |".
  2. ^ a b Galilei, Galileo; translated by Edward Carlos (March 1610). Barker, Peter (ed.). "Sidereus Nuncius" (PDF). University of Oklahoma History of Science. Archived from the original (PDF) on December 20, 2005. Retrieved January 13, 2010.
  3. ^ "In Depth | Ganymede". NASA Solar System Exploration. Archived from the original on July 28, 2018. Retrieved June 16, 2021.
  4. ^ "Ganymede". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
    "Ganymede". Merriam-Webster.com Dictionary. Merriam-Webster.
  5. ^ Quinn Passey & E. M. Shoemaker (1982) "Craters on Ganymede and Callisto", in David Morrison, ed., Satellites of Jupiter, vol. 3, International Astronomical Union, pp. 385–386, 411.
  6. ^ Journal of Geophysical Research, v. 95 (1990).
  7. ^ E. M. Shoemaker et al. (1982) "Geology of Ganymede", in David Morrison, ed., Satellites of Jupiter, vol. 3, International Astronomical Union, pp. 464, 482, 496.
  8. ^ a b c d "Planetary Satellite Mean Orbital Parameters". Jet Propulsion Laboratory, California Institute of Technology. Archived from the original on November 3, 2013. Retrieved February 9, 2008.
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  10. ^ Schubert, G.; Anderson, J. D.; Spohn, T.; McKinnon, W. B. (2004). "Interior composition, structure and dynamics of the Galilean satellites". In Bagenal, F.; Dowling, T. E.; McKinnon, W. B. (eds.). Jupiter: the planet, satellites, and magnetosphere. New York: Cambridge University Press. pp. 281–306. ISBN 978-0521035453. OCLC 54081598. Archived from the original on April 16, 2023. Retrieved July 23, 2019.
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  15. ^ Orton, G. S.; Spencer, G. R.; et al. (1996). "Galileo Photopolarimeter-radiometer observations of Jupiter and the Galilean Satellites". Science. 274 (5286): 389–391. Bibcode:1996Sci...274..389O. doi:10.1126/science.274.5286.389. S2CID 128624870.
  16. ^ Yeomans; Chamberlin. "Horizon Online Ephemeris System for Ganymede (Major Body 503)". California Institute of Technology, Jet Propulsion Laboratory. Archived from the original on February 2, 2014. Retrieved April 14, 2010. (4.38 on 1951-Oct-03).
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  19. ^ Staff (March 12, 2015). "NASA's Hubble Observations Suggest Underground Ocean on Jupiter's Largest Moon". NASA News. Archived from the original on November 5, 2019. Retrieved March 15, 2015.
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  21. ^ Vance, Steve; Bouffard, Mathieu; Choukroun, Mathieu; Sotina, Christophe (April 12, 2014). "Ganymede's internal structure including thermodynamics of magnesium sulfate oceans in contact with ice". Planetary and Space Science. 96: 62–70. Bibcode:2014P&SS...96...62V. doi:10.1016/j.pss.2014.03.011.
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