page_title: Giant planet
section_title: Extrasolar giant planets
hierarchical_section_title: Giant planet / Extrasolar giant planets
caption_attribution_description: An artist's conception of 79 Ceti b (min mass ~0.26 MJ), an exoplanet with a mass less than Saturn.
context_page_description: A giant planet is any planet much larger than Earth. They are usually primarily composed of low-boiling-point materials, rather than rock or other solid matter, but massive solid planets can also exist. There are four known 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, after Jupiter. They are also sometimes known as gas giants. However, many astronomers now apply the latter term only to Jupiter and Saturn, classifying 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.
  The defining differences between a very low-mass brown dwarf and a gas giant are debated. One school of thought is based on formation; the other, on the physics of the interior.
context_section_description: Because of the limited techniques currently available to detect exoplanets, many of those found to date have been of a size associated, in the Solar System, with giant planets. Because these large planets are inferred to share more in common with Jupiter than with the other giant planets, some have claimed that "jovian planet" is a more accurate term for them. Many of the exoplanets are much closer to their parent stars and hence much hotter than the giant planets in the Solar System, making it possible that some of those planets are a type not observed in the Solar System. Considering the relative abundances of the elements in the universe (approximately 98% hydrogen and helium) it would be surprising to find a predominantly rocky planet more massive than Jupiter. On the other hand, models of planetary-system formation have suggested that giant planets would be inhibited from forming as close to their stars as many of the extrasolar giant planets have been observed to orbit.
caption: An artist's conception of 79 Ceti b, the first extrasolar giant planet found with a minimum mass less than Saturn.
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