Gas giant
A gas giant is a huge planet made entirely of base gases, including fluorine, methane, and ammonia. They do not possess a solid surface, but rather have dense atmospheres. These turbulent atmospheres are generally made of the same materials as stars, however, they lack the mass necessary to begin nuclear fusion.

There were several types of gas giants known to Humans: class J, class 6, class 7, and the class 9 gas giant, which was also known to the Klingons as the Q'tahL class. (; )

The Sol system had four gas giants, Jupiter, Saturn, Uranus, and Neptune, none of which were class 9. (, )

The Andorians and Aenar's homeworld of Andoria was a moon that orbited a blue, ringed gas giant.

Gas giants generate intense magnetic fields that often create unique waveforms. The resulting EM interference sounds very strange when played over speakers. Travis Mayweather referred to these sounds as "siren calls," noting that while he lived aboard the  as a kid, his dad would put them through the speakers whenever they flew by a gas giant. ()

Neelix's cousin once had a job transporting disulfides from a gas giant. He enjoyed the turbulence, according to Neelix, who also noted that "disulfides are known to cause delusions." ()

In 2152,  pulled the  from a class J gas giant. () Later that year, they encountered a gas giant in Arkonian space that had "dozens of moons," and was referred to as "like a gravitational jigsaw puzzle." ()

The Xindi-Insectoid assault shuttle discovered in 2154 was discovered to have almost half of its power grid routed to structural integrity, leading the crew of Enterprise to theorize that it could probably be flown inside a gas giant. () 

In the mirror universe, the Tholians held the  at a facility in the Vintaak system that was orbiting the system's lone gas giant. ()

Brown dwarfs were celestial bodies with characteristics that blurred the line between stars and gas giants, and were sometimes referred to as the latter. ()

In 2369, the  was able to witness the collision of two gas giants in the Detrian system, Detria II and Detria VI, which triggered nuclear fusion and formed a new star. ()

Also around this time, Captain Rudolph Ransom eluded a Romulan warbird by taking his vessel into the atmosphere of a gas giant. ()

In 2370, the  became trapped in the atmosphere of a gas giant, Marijne VII, while the crew was attempting to sample it at a low orbit. ()

In 2371, a Maquis interceptor, piloted by the Female Changeling, lured a runabout, piloted by Kira Nerys and Odo, to a moon orbiting the gas giant located near the Badlands. ()

In 2376, the  encounter a class T gas giant within a stellar nursery in the Delta Quadrant. It was surrounded by rings, one of which radiogenic, and Janeway used these particles to reinitialize warp power in the Flyer following a massive antimatter loss. The Flyer and its occupants were later discovered orbiting the gas giant by the . ()

During the Antarian Trans-stellar Rally in 2377, one of the competing ships changed course by using the gravity from a gas giant to boost its speed, and successfully made up for lost ground. ()

The homeworld of Unknown Species 10-C was a gas giant in extragalactic space. The planet was bombarded by asteroids in the 22nd century, destroying the population and stripping away much of the gaseous atmosphere. () The survivors subsequently established a hyperfield around a nearby solar system containing three gas giants, each identical in mass and chemical composition. ()

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Celestial objects