Giant planets are also sometimes called jovian planets, the adjective for the name Jupiter. They are sometimes known as gas giants. Many astronomers use the latter term only for Jupiter and Saturn. They classify Uranus and Neptune, which have different compositions, as ice giants. Both names are potentially misleading: all of the giant planets consist primarily of fluids above their critical points, where distinct gas and liquid phases do not exist. The principal components are hydrogen and helium in the case of Jupiter and Saturn, and water, ammonia and methane in the case of Uranus and Neptune.