Changes

| mdt=1099.06 a<ref name=calc/>

| mdt=1099.06 a<ref name=calc/>

| mhl=761.81<ref name=calc/>

| mhl=761.81<ref name=calc/>

}}'''Ganymede''' ([[Greek]] ''Γανυμήδης'' or ''Ganumedes'') is the largest [[satellite]] of [[Jupiter]] and indeed the largest planetary satellite, by mass or radius, in the [[solar system]]. It is slightly larger than [[Mercury]] (though Mercury is twice as heavy) and is both larger and heavier than any of the [[dwarf planet]]s [[Eris]], [[Pluto]], and [[Ceres]]. Thus, if it orbited the [[Sun]] instead of Jupiter, it might be a true [[planet]]--if it "cleared its neighborhood" of all other objects, as all planets must do to be worthy of the name.

}}'''Ganymede''' ([[Greek]] ''Γανυμήδης'' or ''Ganumedes'') is the largest [[satellite]] of [[Jupiter]] and indeed the largest planetary satellite, by mass or radius, in the [[solar system]]. It is slightly larger than [[Mercury]] (though Mercury is twice as heavy) and is both larger and heavier than any of the [[dwarf planet]]s [[Eris]], [[Pluto]], and [[Ceres]]. Thus, if it orbited the [[Sun]] instead of Jupiter, it might be a true [[planet]]—if it "cleared its neighborhood" of all other objects, as all planets must do to be worthy of the name.

== Discovery and naming ==

== Discovery and naming ==

== Orbital and rotational characteristics ==

== Orbital and rotational characteristics ==

[[Image:Galilean moon Laplace resonance animation.gif|thumb|150 px|left|Orbital resonance of Io, Europa, and Ganymede]]Ganymede is seventh in order of all of Jupiter's moons, and orbits Jupiter at a semi-major axis of 1,070,400 km. Its orbit is very slightly eccentric and slightly inclined to Jupiter's equator. Although Ganymede is in [[tidal lock]] (thus keeping the same face toward Jupiter as it revolves), its axis does tend to tilt very slightly from the true perpendicular from time to time on account of gravitational perturbations.<ref name=Icarus/>

[[Image:Galilean moon Laplace resonance animation.gif|thumb|150 px|left|Orbital resonance of Io, Europa, and Ganymede]]Ganymede is seventh in order of all of Jupiter's moons, and orbits Jupiter at a semi-major axis of 1,070,400&nbsp;km. Its orbit is very slightly eccentric and slightly inclined to Jupiter's equator. Although Ganymede is in [[tidal lock]] (thus keeping the same face toward Jupiter as it revolves), its axis does tend to tilt very slightly from the true perpendicular from time to time on account of gravitational perturbations.<ref name=Icarus/>

The most striking feature of Ganymede's orbit is its three-part [[orbital resonance]] or Laplace resonance with the two inner moons Io and Europa. These three satellites complete their orbits around Jupiter in the ratio 1:2:4. They also conjoin with one another at their apsides, in a mutually self-correcting manner that allows the resonance to persist. (Most such resonances are unstable and end with one or all bodies changing their orbits.)

The most striking feature of Ganymede's orbit is its three-part [[orbital resonance]] or Laplace resonance with the two inner moons Io and Europa. These three satellites complete their orbits around Jupiter in the ratio 1:2:4. They also conjoin with one another at their apsides, in a mutually self-correcting manner that allows the resonance to persist. (Most such resonances are unstable and end with one or all bodies changing their orbits.)

== Physical characteristics ==

== Physical characteristics ==

[[Image:Ganymede G1G2 Interior.jpg|thumb|150px|left|Ganymede cutaway]]Ganymede, as previously noted, is half as massive as [[Mercury]] and more massive by an order of magnitude than either [[Eris]] or [[Pluto]]. Its density is 1,942 kg/m³, which is consistent with a composition that is half water (or water ice) and half rock. Much of the surface is covered with water ice, which produces the light-colored terrain in most true-color images of this moon.<ref name=ambassador>"[http://www.resa.net/nasa/ganymede.htm Ganymede: the Giant Moon]." ''JPL Ambassador Program''. Accessed February 18, 2008.</ref>

[[Image:Ganymede G1G2 Interior.jpg|thumb|150px|left|Ganymede cutaway]]Ganymede, as previously noted, is half as massive as [[Mercury]] and more massive by an order of magnitude than either [[Eris]] or [[Pluto]]. Its density is 1,942&nbsp;kg/m³, which is consistent with a composition that is half water (or water ice) and half rock. Much of the surface is covered with water ice, which produces the light-colored terrain in most true-color images of this moon.<ref name=ambassador>"[http://www.resa.net/nasa/ganymede.htm Ganymede: the Giant Moon]." ''JPL Ambassador Program''. Accessed February 18, 2008.</ref>

The model of Ganymede's interior has its basis in this most striking finding: Ganymede and Io, unique among all planetary satellites, have their own magnetic fields. This is most consistent with Ganymede having a metallic core, most likely of iron and iron sulfate.<ref name=Showman2>Showman, Adam P., and Malhotra, Renu. "[http://www.lpl.arizona.edu/~showman/publications/showman-malhotra-1999.pdf The Galilean Satellites]." ''Science'', 286: 77–84, 1999. Accessed February 18, 2008.</ref> Surrounding this core is a mantle of ice and silicates and an outer mantle of ice.

The model of Ganymede's interior has its basis in this most striking finding: Ganymede and Io, unique among all planetary satellites, have their own magnetic fields. This is most consistent with Ganymede having a metallic core, most likely of iron and iron sulfate.<ref name=Showman2>Showman, Adam P., and Malhotra, Renu. "[http://www.lpl.arizona.edu/~showman/publications/showman-malhotra-1999.pdf The Galilean Satellites]." ''Science'', 286: 77–84, 1999. Accessed February 18, 2008.</ref> Surrounding this core is a mantle of ice and silicates and an outer mantle of ice.

Ganymede appears to have a strong inductive magnetic moment. Its ''permanent'' equatorial magnetic flux density is 7.19 milligauss, stronger than that measured at any other moon. This is consistent with a magnetic dipole moment of 1.31 * 10²⁰ N-m/T. The magnetic dipole moment ''at creation'' was probably 3.49 * 10²² N-m/T, consistent with a decay time of about 1099 years and a half-life of 762 years.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref>

Ganymede appears to have a strong inductive magnetic moment. Its ''permanent'' equatorial magnetic flux density is 7.19 milligauss, stronger than that measured at any other moon. This is consistent with a magnetic dipole moment of 1.31 * 10²⁰ N-m/T. The magnetic dipole moment ''at creation'' was probably 3.49 * 10²² N-m/T, consistent with a decay time of about 1099 years and a half-life of 762 years.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref>

However, the permanent magnetic moment does not account for all the magnetic fluxes on Ganymede. Ganymede lies well within Jupiter's magnetic field, and this field is likely inducing an electrical current within a conducting shell having a radius almost as long as that of Ganymede itself. This shell is probably a conductive liquid between the crust and the core, most likely a saltwater ocean about 146 km deep to the surface and extending to the outer mantle.<ref name=Kivelson/><ref name=jplocean>"[http://www.jpl.nasa.gov/releases/2000/aguganymederoundup.html Solar System's Largest Moon Likely Has a Hidden Ocean]." Press release 12/12/00 GW 00-XXX, [[JPL]], [[NASA]], December 12, 2000. Accessed February 18, 2008.</ref>

However, the permanent magnetic moment does not account for all the magnetic fluxes on Ganymede. Ganymede lies well within Jupiter's magnetic field, and this field is likely inducing an electrical current within a conducting shell having a radius almost as long as that of Ganymede itself. This shell is probably a conductive liquid between the crust and the core, most likely a saltwater ocean about 146&nbsp;km deep to the surface and extending to the outer mantle.<ref name=Kivelson/><ref name=jplocean>"[http://www.jpl.nasa.gov/releases/2000/aguganymederoundup.html Solar System's Largest Moon Likely Has a Hidden Ocean]." Press release 12/12/00 GW 00-XXX, [[JPL]], [[NASA]], December 12, 2000. Accessed February 18, 2008.</ref>

In 1995, the [[Hubble Space Telescope]] team developed evidence for the manufacture of [[ozone]] on Ganymede.<ref name=HST>Villard, Ray, and Noll, Keith. "[http://www.solarviews.com/eng/ganypr.htm Hubble Finds Ozone on Jupiter's Moon Ganymede]." Press release STScI-PR95-36, October 10, 1995. Reproduced at ''Solarviews''. Accessed February 18, 1995.</ref> Speculation on the origin of this ozone has centered on radioactive particles trapped within Jupiter's own magnetic field in a Van Allen-type radiation belt that actually extends beyond Ganymede's orbit.

In 1995, the [[Hubble Space Telescope]] team developed evidence for the manufacture of [[ozone]] on Ganymede.<ref name=HST>Villard, Ray, and Noll, Keith. "[http://www.solarviews.com/eng/ganypr.htm Hubble Finds Ozone on Jupiter's Moon Ganymede]." Press release STScI-PR95-36, October 10, 1995. Reproduced at ''Solarviews''. Accessed February 18, 1995.</ref> Speculation on the origin of this ozone has centered on radioactive particles trapped within Jupiter's own magnetic field in a Van Allen-type radiation belt that actually extends beyond Ganymede's orbit.