Animation of Jupiter磗 moon Ganymede passing in front of the planet. Ganymede is the largest moon in the Solar System, with a diameter of some 5200 kilometres. It is the third Galilean moon from Jupiter, orbiting some 1.07 million kilometres from the centre of the planet. Its surface is a combination of old, cratered dark regions and only slightly younger, lighter ice_rich regions marked with grooves. It is thought that the surface lies on top of an ocean of liquid water.