The four gas giants of the solar system are, in order of increasing distance from the Sun, Jupiter, Saturn, Uranus, and Neptune. Jupiter illustrates why the term "gas giant" (coined by the science fiction writer James Blish) is somewhat of a misnomer. Apart from having a sizeable solid core, Jupiter also has much of its hydrogen in either liquid or, at greater depths, solid, quasi-metallic form.
Most of the extrasolar planets discovered so far appear to be gas giants, though this is a selection effect stemming from the fact that current detection methods are heavily biased toward finding massive planets. The upper mass limit of a gas giants is thought to be around 13 times the mass of Jupiter. Above this, theory suggests that the pressure inside an object is sufficient to induce a modest level of deuterium fusion, which produces enough heat for the object to glow dully as a brown dwarf. Gas giants are also referred to as jovians or as Jupiter-type planets.
Formation of gas giants
All of the stars in the study, including those as young as a few million years, have less than 10 percent of Jupiter's mass in gas swirling around them. This indicates that gas giant planets like Jupiter and Saturn have already formed in these young solar system analogs, or they never will.
Related category PLANETS AND MOONS
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