Illustration of chunks of rock and ice in Saturn's rings. Saturn is seen behind the rings. The most visible rings extend outwards from Saturn for around 120,000 kilometres. The rings, only about one kilometre thick, consist of millions of rock and ice chunks. They are thought to have formed from the disintegration of a moon that was too close to Saturn, or was hit by a comet or asteroid. Saturn, the sixth planet from the Sun, is mostly hydrogen and helium.