This image of Jupiter's largest moon, Ganymede, was taken by the Voyager 2 spacecraft during its encounter with Jupiter in 1979. The dark areas are older and the light areas are younger. The bright spots are recent impact craters and their ejecta. Ganymede is Jupiter's largest moon and is also the largest moon in the Solar System. It is about 50% larger than Earth's moon and is actually larger then the planet Mercury.
NASA / JPL image