MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Diagram showing the theoretical interior of the gas giant planet Saturn 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, about half of the planet's total radius, of liquid metallic hydrogen under great pressure. On top of this is the thick outer mantle, a layer of liquid molecular hydrogen and helium, and finally an extensive hydrogen-helium atmosphere.
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