Ice giant

An ice giant is a <a href="/facts/Giant_planet/PjSfFuUF">giant planet</a> composed mainly of elements heavier than <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> and <a href="/facts/Helium/yRul93TG">helium</a>, such as <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, <a href="/facts/Carbon/ukrgQexo">carbon</a>, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, and <a href="/facts/Sulfur/IK0amTfM">sulfur</a>. There are two ice giants in the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a>: <a href="/facts/Uranus/x7YwT1ar">Uranus</a> and <a href="/facts/Neptune/1eucwHIC">Neptune</a>.
In <a href="/facts/Astrophysics/krFPRWLA">astrophysics</a> and <a href="/facts/Planetary_science/ocX6rp0d">planetary science</a> the term "ice" refers to volatile chemical compounds with freezing points above about 100 <a href="/facts/Kelvin/E3trzC4C">K</a>, such as <a href="/facts/Water/0lkXnJPK">water</a>, <a href="/facts/Ammonia/MtLtJFtz">ammonia</a>, or <a href="/facts/Methane/kBHneYnh">methane</a>, with freezing points of 273 K (0 °C), 195 K (−78 °C), and 91 K (−182 °C), respectively (see <a href="/facts/Volatile_(astrogeology)/yYCe49qX">Volatiles</a>). In the 1990s, it was determined that Uranus and Neptune were a distinct class of giant planet, separate from the other giant planets, <a href="/facts/Jupiter/95m7XjMT">Jupiter</a> and <a href="/facts/Saturn/D54LcGJ9">Saturn</a>, which are <a href="/facts/Gas_giant/pmF6KztG">gas giants</a> predominantly composed of hydrogen and helium.
Neptune and Uranus are now referred to as ice giants. Lacking well-defined solid surfaces, they are primarily composed of gases and liquids. Their constituent compounds were solids when they were primarily incorporated into the planets during their formation, either directly in the form of ice or trapped in water ice. Today, very little of the water in Uranus and Neptune remains in the form of ice. Instead, water primarily exists as <a href="/facts/Supercritical_fluid/rGkUWb7e">supercritical fluid</a> at the temperatures and pressures within them. Uranus and Neptune consist of only about 20% hydrogen and helium by mass, compared to the Solar System's <a href="/facts/Gas_giant/pmF6KztG">gas giants</a>, Jupiter and Saturn, which are more than 90% hydrogen and helium by mass.

Ice giant open-in-new

Ice giant