one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. (nationalgeographic.org)
Planetary scientists are finding that the four outermost planets of our solar system haven't always been orbiting where they are today. (science.sciencemag.org)
However, its large outermost planet could have long ago swept that vicinity clean of planetary material, notes planetary scientist Jonathan Lunine of the University of Arizona at Tucson. (scientificamerican.com)