Transcript: Jupiter's Ganymede is the largest moon in the solar system, just under 5,300 kilometers in diameter. That's 8 percent larger than Mercury and twice the size of tiny Pluto. Ganymede has an old fractured surface covered in groves and fissures. This dark surface is heavily cratered and fairly old. But also, watery material has apparently erupted on the surface of Ganymede at some point in the past to form deposits. In some cases the gray surface soils have been blasted away by meteoric impacts to reveal the whiter ice. The possibility of water and ice on Ganymede is very exciting. Ganymede’s orbit is too circular for tidal heating to have created the heat needed to make water ice erupt. However, its orbit may have had irregularities in the past that could have led to tidal heating.