Gas giant it has the right temperature. Gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are sometimes known as failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet", but in the 1990s it became known that Uranus and Neptune are really a distinct class of giant planet, being composed mainly of heavier volatile substances (which are referred to as "ices"). For this reason, Uranus and Neptune are now often
Sudarsky's gas giant classification Sudarsky's gas giant classification Sudarsky's classification of gas giants for the purpose of predicting their appearance based on their temperature was outlined by David Sudarsky and colleagues in the paper "Albedo and Reflection Spectra of Extrasolar Giant Planets" and expanded on in "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets", published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas-giant atmospheres. Gas giants are split into five classes (numbered using Roman numerals) according to