A satellite of a ringed planet whose gravitational field has a significant effect on the configuration of planetary rings near it. Shepherd moons were first discovered on Voyager images of Saturn. Saturn's F Ring is kept very narrow by two shepherd satellites, Pandora and Prometheus, which orbit either side of it. Uranus's outer ring, the Epsilon Ring, is kept in place by the shepherd moons Ophelia and Cordelia.
Subjects: Astronomy and Astrophysics.