Diagram showing the theoretical interior of the gas giant planet Jupiter. At the centre there is probably a rocky and icy core several times the mass of the Earth. This is surrounded by an extensive inner mantle, more than two-thirds of the planet's total radius, of liquid metallic hydrogen under great pressure. On top of this is the outer mantle, a layer of liquid molecular hydrogen and helium, and finally an extensive hydrogen-helium atmosphere about 1000 km thick.