Figure 11.3 Interior structure of Uranus.

density of Uranus is about 1.3 g/cm3, about one-quarter that of Earth. Thus the material Uranus is made out of must be light and icy.

In contrast to the other gas planets (Jupiter and Saturn), the composition of Uranus is not dominated by hydrogen and helium. Hydrogen accounts for only 15 per cent of the planet's mass. Most of the planet is made up of methane, ammonia and water. There are three layers or regions inside the planet. The dense core (30%) contains rock and various ices, but no liquid metallic hydrogen. The mantle (40%) is probably highly compressed water ice with some methane and ammonia. The outer layer (30%) lies at the base of the atmosphere and is considered to be composed of mostly icy molecules of water, methane and ammonia.

The strength of gravity on Uranus is less than on Earth (8.2 N/kg compared to Earth's 9.8 N/kg). This means that a 75 kg person who weighs 735 N on Earth would weigh only 615 N on Uranus.

Being a gaseous planet, there is no solid surface layer on Uranus. The outer layer of the planet is probably made up of icy molecules of of water,

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