![]() ![]() Cold gas giants Ī cold hydrogen-rich gas giant more massive than Jupiter but less than about 500 M Earth ( 1.6 M J) will only be slightly larger in volume than Jupiter. Hot Jupiters are class IV or V.Įxtrasolar Artist's impression of the formation of a gas giant around the star HD 100546 A gas giant exoplanet with the density of a marshmallow has been detected in orbit around a cool red dwarf star by the NASA-funded NEID radial-velocity instrument on the 3.5-meter WIYN Telescope at Kitt Peak National Observatory. Theoretically, gas giants can be divided into five distinct classes according to their modeled physical atmospheric properties, and hence their appearance: ammonia clouds (I), water clouds (II), cloudless (III), alkali-metal clouds (IV), and silicate clouds (V). Main article: Sudarsky's gas giant classification In this terminology, since Uranus and Neptune are primarily composed of ices, not gas, they are more commonly called ice giants and distinct from the gas giants. ![]() In the outer Solar System, hydrogen and helium are referred to as "gases" water, methane, and ammonia as "ices" and silicates and metals as "rocks". The term has nevertheless caught on, because planetary scientists typically use "rock", "gas", and "ice" as shorthands for classes of elements and compounds commonly found as planetary constituents, irrespective of what phase the matter may appear in. Other than solids in the core and the upper layers of the atmosphere, all matter is above the critical point, where there is no distinction between liquids and gases. It is, arguably, something of a misnomer because throughout most of the volume of all giant planets, the pressure is so high that matter is not in gaseous form. The term gas giant was coined in 1952 by the science fiction writer James Blish and was originally used to refer to all giant planets. Part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history. One school of thought is based on formation the other, on the physics of the interior. The defining differences between a very low-mass brown dwarf (which can have a mass as low as roughly 13 times that of Jupiter ) and a gas giant are debated. The gas giants' cores are thought to consist of heavier elements at such high temperatures (20,000 K ) and pressures that their properties are not yet completely understood. ![]() The layer of metallic hydrogen located in the mid-interior makes up the bulk of every gas giant and is referred to as "metallic" because the very large atmospheric pressure turns hydrogen into an electrical conductor. The outermost portion of their hydrogen atmosphere contains many layers of visible clouds that are mostly composed of water (despite earlier certainty that there was no water anywhere else in the Solar System) and ammonia. They are thought to consist of an outer layer of compressed molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core inside. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of their mass. For this reason, Uranus and Neptune are now often classified in the separate category of ice giants. However, in the 1990s, it became known that Uranus and Neptune are really a distinct class of giant planets, being composed mainly of heavier volatile substances (which are referred to as " ices"). The term "gas giant" was originally synonymous with " giant planet". ![]() Jupiter and Saturn are the gas giants of the Solar System. Gas giants are also called failed stars because they contain the same basic elements as a star. Saturn at equinox, photographed by Cassini in August 2009Ī gas giant is a giant planet composed mainly of hydrogen and helium. ![]()
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