Editing Giant planet (section)

== Terminology ==
The term ''gas giant'' was coined in 1952 by science fiction writer [[James Blish]] and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of these planets the pressure is so high that matter is not in gaseous form.<ref name="d'angelo2011"/> Other than the upper layers of the atmosphere,<ref name="d'angelo2021"/> all matter is likely beyond the [[critical point (thermodynamics)#Liquid–vapor critical point|critical point]], where there is no distinction between liquids and gases. ''Fluid planet'' would be a more accurate term. Jupiter also has [[metallic hydrogen]] near its center, but much of its volume is hydrogen, helium, and traces of other gases above their critical points. The observable atmospheres of all these planets (at less than a unit [[optical depth]]) are quite thin compared to their radii, only extending perhaps one percent of the way to the center. Thus, the observable parts are gaseous (in contrast to [[Mars]] and Earth, which have gaseous atmospheres through which the crust can be seen).

The rather misleading term has 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 the matter's [[phase of matter|phase]]. In the outer Solar System, hydrogen and helium are referred to as ''gas''; water, methane, and ammonia as ''ice''; and silicates and metals as ''rock''. When deep planetary interiors are considered, it may not be far off to say that, by ''ice'' astronomers mean [[oxygen]] and [[carbon]], by ''rock'' they mean [[silicon]], and by ''gas'' they mean hydrogen and helium. The many ways in which Uranus and Neptune differ from Jupiter and Saturn have led some to use the term only for planets similar to the latter two. With this terminology in mind, some astronomers have started referring to Uranus and Neptune as [[ice giant]]s to indicate the predominance of the ''ices'' (in fluid form) in their interior composition.<ref name="NASAames2006"/>

The alternative term ''jovian planet'' refers to the Roman god [[Jupiter (mythology)|Jupiter]]—the genitive form of which is ''Jovis'', hence ''Jovian''—and was intended to indicate that all of these planets were similar to Jupiter.

Objects large enough to start [[deuterium]] [[Nuclear fusion|fusion]] (above 13 [[Jupiter mass]]es for solar composition) are called [[brown dwarf]]s, and these occupy the mass range between that of large giant planets and the lowest-mass [[star]]s. The 13-Jupiter-mass ({{Jupiter mass}}) cutoff is a rule of thumb rather than something of precise physical significance. Larger objects will burn most of their deuterium and smaller ones will burn only a little, and the {{jupiter mass|link=yes|13}} value is somewhere in between.<ref name="bodenheimer2013"/> The amount of deuterium burnt depends not only on the mass but also on the composition of the planet, especially on the amount of [[helium]] and deuterium present.<ref name="spiegel2011"/> The [[Extrasolar Planets Encyclopaedia]] includes objects up to 60 Jupiter masses, and the [[Exoplanet Data Explorer]] up to 24 Jupiter masses.<ref name="schneider2016"/><ref name="wright2010"/>