Saturn and its rings. Saturn, the sixth planet from the Sun, is a gas giant, composed mostly of helium and hydrogen. With a diameter nearly ten times that of the Earth it is the second largest planet in the Solar System. Its rings, which span almost 300,000 kilometres, are composed of ice and rock particles. The largest gap in the rings is the Cassini division, which separates the A (outer) and B (inner) rings. Image taken in 2006.