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Saturn: Interior Structure

Saturn's mean density of 0.69 g cm−3 is the lowest of any object in the solar system. Like Jupiter and the Sun, Saturn is composed primarily of the light gases hydrogen and helium. If Saturn had the same chemical composition as the Sun, out of a total mass of 95 Earth masses, it would contain about 68 Earth masses of hydrogen, about 26 Earth masses of helium and about one Earth mass of all other elements (the so-called heavy elements). Models of the interior of Saturn indicate, however, that the planet actually contains about 29 Earth masses of heavy elements, with about 48 Earth masses of hydrogen and 18 Earth masses of helium. Saturn is, therefore, considerably more depleted in the light gases hydrogen and helium than Jupiter. If this is the case, why is Saturn's mean density so low, only half that of Jupiter's? The answer comes from consideration of the very high compressibility of hydrogen under the conditions in the interior of Saturn or Jupiter. Saturn's