Wednesday, March 31, 2010

More Rings on the Far Planets

During a 1977 Earth-based observation of Uranus in the course of a stellar occultation (the passage of Uranus in front of the star), the star’s light dimmed several times before disappearing behind the planet. That dimming of the star’s light revealed the presence of nine thin, faint rings around the planet. Voyager 2 revealed another pair. Uranus’s rings are very narrow—most of them less than 6 miles (10 km) wide—and are kept together by the kind of shepherd satellites that are found outside of Saturn’s F ring. Neptune has rings similar to those of Uranus.