Prometheus is a
shepherd satellite for the inner edge of Saturn's narrow
F Ring.
Pandora orbits just outside the F Ring, and has traditionally been viewed as an outer shepherd of the ring; however, recent studies indicate that only Prometheus contributes to the confinement of the ring. Images from the
Cassini probe show that Prometheus's gravitational influence creates kinks and knots in the F Ring as it shepherds material from it. The orbit of Prometheus appears to be chaotic, due to a series of four 121:118
mean-motion resonances with
Pandora. The most appreciable changes in their orbits occur approximately every 6.2 years, when the
periapsis of Pandora lines up with the apoapsis of Prometheus, as they approach to within approximately 1400 km. Prometheus is itself a significant perturber of
Atlas, with which it is in a 53:54 mean-longitude resonance. Prometheus also participates in a 17:15
mean-motion resonance with
Epimetheus, but only while it is on the outer orbit relative to
Janus. No such configuration with Janus exists. Due to their gravitational interactions with the rings, Prometheus and Pandora are expected to crash into each other or Mimas in the next 20 million years. == Physical characteristics ==