Giant planet

Saturoneptuna: Jupiter and Saturn (gas giants) Uranus and Neptune (ice giants) Shown in order from the Sun and in true color. Sizes are not to scale.

A giant planet is any planet much larger than Earth. They are usually mostly composed of low-boiling-point materials (gases or ices), rather than rock or other solid matter. Massive solid planets also exist. There are four giant planets in the Solar System: Jupiter, Saturn, Uranus and Neptune. Many extrasolar giant planets have been identified orbiting other stars.

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.^[1] 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.

The defining differences between a very low-mass brown dwarf and a gas giant are not clear.^[2] One school of thought is based on formation; the other, on the physics of the interior.^[2] Part of the debate is whether "brown dwarfs" must, by definition, have had nuclear fusion at some point in their history.

1. ↑ Lunine, Jonathan I. (September 1993). "The Atmospheres of Uranus and Neptune". Annual Review of Astronomy and Astrophysics. 31: 217–263. Bibcode:1993ARA&A..31..217L. doi:10.1146/annurev.aa.31.090193.001245.
2. ↑ ^{2.0 2.1} Burgasser, A. J. (June 2008). "Brown dwarfs: Failed stars, super Jupiters" (PDF). Physics Today. Archived from the original (PDF) on 8 May 2013. Retrieved 11 January 2016.