Ganymede. Jupiter Moons. Ganymede is the biggest moon in the solar system and, in fact, is larger than the planets Mercury and Pluto. It has two distinct surface types - one dark and rugged, the other bright and smooth, with parallel grooves hundreds of meters deep and thousands of kilometers long. The bright areas show fewer impact craters, indicating a much newer terrain, possibly resurfaced by ice volcanoes.
Photo : NASA JPL HST