Uranus

Uranus is the third biggest planet, and is four times bigger across than Earth. It is so far from the Earth that is barely visible with the naked eye. Because of this it was not discovered until the 1700s, with the help of telescope.

Uranus has a thick atmosphere of hydrogen, helium and methane, and a mantle of water, ammonia and methane ice. At the centre there is an irom silicate core.

Astronomers used to think that Saturn was the only planet thathad rings circling it. But, in 1977, they discovered that Uranus had rings too. There are about 11 main rings, made up of bits of rock up to a metre across, which whizz round the planet at high speed. The particles in some of the rings are kept in place by tiny 'shepherd' moons.