Glossary of Astronomical Terms/gas giant

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Gas giant is a generic term applied to large planets whose atmospheres comprise a significant proportion of their total mass. This term is generally used to refer to Jupiter, Saturn, Uranus, and Neptune in our own solar system.

Contrary to popular perception, gas giants are not entirely gaseous; Jupiter and Saturn are believed to have small rocky cores and "oceans" of liquid hydrogen while Uranus and Neptune contain more rock and ice than gas.