A disk of matter encircling a planet, consisting of numerous particles in orbit ranging in size from dust grains up to objects tens of metres across. In the Solar System, Saturn has the brightest and most extensive rings, composed mainly of ice. In 1979 the Voyager probes detected a ring around Jupiter. Rings were found around both Uranus and Neptune by stellar occultations, and confirmed when Voyager 2 visited them. The various planetary rings have different proportions of ice and dust, and different distributions of particle sizes. Planetary rings may consist of debris from impacts on the planets’ satellites.

http://planetarynames.wr.usgs.gov/Page/Rings Names and data of planetary rings.