A gas giant is a type of planet which is composed mainly of gases such as fluorine, methane and ammonia. The United Federation of Planets classifies such planets as class J, class 6, class 7, and class 9.
The planets are generally anywhere from 2 billion to 10 billion years old, and have a diameter of 50,000 km to 140,000 km. Often these planets have a solid rocky or metallic core. Gas giants are usually found in the cold zone of an ecosphere of a star system. (ST reference: Star Charts)
As giants are made up of the same materials found in stars, however they are not large enough to sustain nuclear fusion and become stars. It has been demonstrated that if two gas giants collide, the large mass involved could become dense enough to begin a self-sustaining nuclear reaction - creating a new star in the process. (TNG episode: "Ship in a Bottle")
- The Bajor system has three gas giants, Bajor IX, Bajor X and Bajor XI. (DS9 reference: Star Trek: Deep Space Nine Technical Manual, ST reference: Star Charts)
- A large gas giant was one of the inner planets which orbited Pantera before the star went nova. (TNG eBook: A Sea of Troubles)