Model of the internal structure of the planet Uranus. Uranus is the second most distant planet from the Sun, orbiting at just under 20 times the Earth_Sun distance. It is some 51,120 kilometres in diameter, just over four times Earth磗 diameter. It has a thin ring system. The tops of its clouds are largely featureless. Beneath these clouds is a thick atmosphere of hydrogen, helium and methane light green. Below that is a thick layer of 磇ces?dark green, largely water, ammonia and methane that exist as a hot, dense liquid. At its centre is a rocky core grey, formed of iron, nickel and silicates. Uranus磗 greenish colour comes from traces of methane, which absorbs red light.