Ganymede

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• Ganymede turned out to be the largest satellite in the solar system. Before the Voyager encounters, astronomers thought that Saturn's satellite, Titan, was the largest. Ground-based observations of Titan, of necessity, had included its substantial atmosphere. Voyager measurements of Ganymede showed it is larger than Titan. Ganymede had two distinct terrain types --- cratered and grooved, telling scientists that Ganymede's entire, ice-rich crust has been under tension from global tectonic processes