Ganymede Up Close & Personal

Ganymede - the largest moon in the solar system, even bigger than the planet Mercury - can be seen in astonishing detail by NASA's Galileo probe. The icy surface has a cratered terrain with light and dark spots, and the large circular feature on the upper right is known as Galileo Regio, although its origin is unknown. This image was taken 20 years ago, but as various space organizations look to study more about the icy Jovian moons, hopefully soon its secrets will be revealed (perhaps even liquid water?).