Ice giant

Neptune is an ice giant.

An ice giant is a huge planet made mostly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two known ice giants in the Solar System, Uranus and Neptune.

In astrophysics and planetary science the term "ice" refers to volatile chemical compounds with freezing points above about 100 K (−280 °F; −173 °C), such as water, ammonia, or methane, with freezing points of 273, 195, and 91 K (31.7, −108.7, and −295.9 °F; −0.1, −78.1, and −182.2 °C), respectively.

In the 1990s, it was realized that Uranus and Neptune are a distinct class of giant planet, different from the other giant planets, Jupiter and Saturn. They have become known as ice giants. They were solids when the planets were stuck together during their formation. Today, little of the water in Uranus and Neptune is in the form of ice. Instead, the water is a supercritical fluid at the temperatures and pressures inside them.

Ice giants consist of only about 20% hydrogen and helium in mass, as opposed to the Solar System's gas giants, Jupiter and Saturn, which are both more than 90% hydrogen and helium in mass.

Ice Giant Media

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  These cut-aways illustrate interior models of the giant planets. The planetary cores of gas giants Jupiter and Saturn are overlaid by a deep layer of metallic hydrogen, whereas the mantles of the ice giants Uranus and Neptune are composed of heavier elements.