This close-up image of Jupiter's moon Ganymede was taken by NASA's Voyager 2 spacecraft during its encounter in 1979. It shows the hemisphere of the moon that faces away from the Sun. The dark area at the upper left is known as Regio Galileo. Below it, the bright areas are cause when asteroid and meteor impacts reveal water ice from beneath the crust. Ganymede is very similar to Earth's moon in that it is composed of older darker material with lighter, younger areas cased by more recent geological activity.