Abstract
The narrow rings are thought to be stabilised by small shepherd moons that orbit in or near the rings and stabilize them by gravitational influences. The narrow F ring of Saturn which lies just outside the spectacular main rings is tended by two small shepherds. Prometheus (100 km in diameter) orbits just inside the F ring, while Pandora (85 km in diameter) moves around Saturn just outside the F ring. Images from the Saturn F ring region obtained by the Cassini Imaging Science Subsystem (ISS) cameras have revealed structure never seen before in a planetary ring. Periodic structures such as azimuthal gaps, channels of low optical depth and streamers have been discovered. We reported these features previously in Murray et al. (2005). Updated orbits are used here. The orbit of Prometheus has been taken from Spitale et al. (2006), the orbit of the F ring core from Bosh et al. (2002). The dimensions and mass of Prometheus have been taken from Porco et al. (2006). We made a direct comparison between the previous numerical results using the orbits reported in Murray et al. (2005) and our model for the same configuration, and we find an excellent agreement.
