- See Class J for other uses of this term.
In planetary classification, a class J planet is a gas giant. Gas giants have an age ranging from 2-10 billion years and a diameter between 50,000 and 140,000 km. They are located within the Cold Zone of a star system. A class J planet is characterized by a tenuous surface, comprised of gaseous hydrogen and some hydrogen compounds, and an atmosphere comprised of zones that vary in temperature and composition. The only known lifeforms to be found on J-class planets are hydrocarbon-based. Examples of Class J planets include Jupiter and Saturn. (Star Trek Star Charts)
In 2372, the USS Defiant entered the atmosphere of a class J planet to rescue the crew of a Karemma ship. The Karemmans were attempting to escape from two Jem'Hadar ships. (DS9: "Starship Down")