![]() But Uranus and Neptune are almost all core, without the deep envelope of hydrogen and helium that make up most of the mass of Jupiter and Saturn. Uranus and Neptune are not unlike the cores of Jupiter and Saturn, which similarly contain 10 to 20 Earth masses of melted ice and molten rock. These molecules will form from atoms of hydrogen, H, oxygen, O, carbon, C, and nitrogen, N, the most abundant heavy elements in the material from which the Sun and giant planets originated. Although customarily denoted as ices, since they would be frozen at the cloud tops of these planets, these substances are kept liquid by the high temperatures, up to 8,000 degrees kelvin, deep in the planetary interiors. Most of their interior probably consists of a vast internal ocean of water, H 2O, methane, CH4, and ammonia, NH 3. So there is no internal shell of liquid metallic hydrogen inside Uranus and Neptune. These two planets do not have enough hydrogen, or sufficient mass and internal pressure, to squeeze the hydrogen into a metallic state. The hydrogen in Uranus and Neptune is confined within a thin atmosphere and liquid molecular shell that do not extend to great depths and contribute only about 15 percent of the planetary mass. But they must be quite different from Jupiter and Saturn inside. Since Uranus and Neptune have similar mass, size, composition and rotation, their interiors are also expected to be alike. To put it another way, both planets are too small for their mass to be mainly composed of hydrogen and helium, and must consist mainly of heavier material. For their size, Uranus and Neptune are too massive for hydrogen to be their main ingredient, and their bulk must instead be composed of heavier abundant elements. ![]() ![]() Unlike Jupiter and Saturn, however, Uranus and Neptune cannot consist mostly of the lightest element hydrogen, or they would have a lower mean mass density then observed. The overwhelming abundance of hydrogen in the outer atmospheres of Uranus and Neptune resembles that in Jupiter, Saturn and the Sun. The tenuous gas forms an extensive hydrogen corona around Uranus, but is held closer to the cloud tops above Neptune. The atmosphere above the cloud tops of Uranus and Neptune consists mainly of molecular and atomic hydrogen, warmed by the Sun’s ultraviolet rays. Uranus and Neptune Interiors and magnetic fields
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