If Uranus and Neptune were also of solar composition—that is, if they were made primarily of hydrogen and helium—their average densities would be less than half the density of water, even less than that of Saturn. Their lower mass would not be as effective as Saturn’s in compressing their hydrogen and helium. But Uranus and Neptune are observed to be about twice as dense as Saturn (see Table 10.1). This is a clear indication that, unlike Jupiter and Saturn, Uranus and Neptune must have denser material dominating their chemical composition. Observations should indicate whether this denser material is water or rock. Neptune, the densest of the giant planets, is about 1.5 times as dense as uncompressed water and only about half as dense as uncompressed rock. Uranus is even less dense than Neptune. These observations indicate that both Uranus and Neptune must contain more water than rock.
If Uranus and Neptune were also of solar composition—that is, if they were made primarily of hydrogen and helium—their average densities would be less than half the density of water, even less than that of Saturn. Their lower mass would not be as effective as Saturn’s in compressing their hydrogen and helium. But Uranus and Neptune are observed to be about twice as dense as Saturn (see Table 10.1). This is a clear indication that, unlike Jupiter and Saturn, Uranus and Neptune must have denser material dominating their chemical composition. Observations should indicate whether this denser material is water or rock. Neptune, the densest of the giant planets, is about 1.5 times as dense as uncompressed water and only about half as dense as uncompressed rock. Uranus is even less dense than Neptune. These observations indicate that both Uranus and Neptune must contain more water than rock.
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