Gas ultragiant

Size: 100,000 km - 500,000 km
Atmosphere composition: Varies

Usually found in a star's cold zone, although many have been found on surprisingly close orbits to their primaries. They have high core temperatures causing them to radiate enough heat to keep water in a liquid state. These are the largest possible planets, as more massive bodies generate enough core heat to initiate fusion reactions and become stars.

If large enough, this type of world may also be called a small brown dwarf.