Saturn from Rhea. Computer artwork of the ringed gas giant plant Saturn (centre left) seen from the cratered surface of Rhea, one of its moons. The Sun (far right) is around 1430 million kilometres away, more than 9.5 times as distant as it is from Earth. This leads to very low temperatures that allow the formation of moons, such as Rhea, that consist of rock and ices. Ices is the term for the substances ammonia, water and methane, when they are found frozen in the outer solar system. Rhea is thought to be mainly water ice with rock making up about one third of it. Rhea orbits Saturn at around 527,000 kilometres and, at 1530 kilometres across, is the second largest of Saturn's moons.