6. Jupiter's Moon, Ganymede
7. Jupiter's Moon, Ganymede
6. Jupiter's Moon, Ganymede

6. Jupiter's Moon, Ganymede

produced by DLR (German Aerospace Center), Berlin

http://photojournal.jpl.nasa.gov/catalog/PIA02577


Forty percent of the surface of Ganymede is covered by highly-cratered dark regions, and the remaining sixty percent is covered by a light grooved terrain which forms intricate patterns across Ganymede. The dark regions on Ganymede are old and rough and believed to be the original crust of the satellite. Lighter regions are young and smooth (unlike Earth's Moon).
Since Ganymede has a low density, it was originally estimated that the satellite is half water ice with a rocky core extending to half of the satellite's radius. However, the Galileo spacecraft found a magnetic field around Ganymede, which strongly indicates that the satellite has metallic core about 250 to 800 miles in. The mantle is composed of ice and silicates and a crust which is probably a thick layer of water ice.