Named after the cup-bearer to the Greek gods on Mt Olympus, Ganymede is the largest moon in our solar system. At 3,280 miles in diameter, it's over one and a half times the size of our moon, even larger than the planet Mercury.

The recent discovery of a magnetosphere around Ganymede indicates the moon has a metallic core of iron or iron alloy. On top of the core lies a mantle of ice and silicates.

The surface crust of Ganymede is composed of a thick layer of water ice.