Ganymede

Ganymede is not only Jupiter's largest moon, it is the largest moon in the Solar System. With a radius of 2634 km and a mass of 1.48e23 kg, Ganymede is larger than Mercury but it has only about half the mass. This large moon has three layers - it is made up of an icy shell around a rocky silicate mantle all surrounding a small core of either molten iron or iron/sulfur.