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[[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 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, unique among all planetary satellites, has its own magnetic field. 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>