Prometheus and the F Ring at Saturn. This interesting view is one of Prometheus, a shepherd moon of Saturn. Prometheus is an oblong body which is orbiting just inside the F ring. The F ring is a faint outer ring in Saturn's ring system. The ring system, generally is shepherded and gravitationally affected by small, inner, irregular satellites and by a part of the regular satellites like Mimas. Some of the inner moons are orbiting near or inside the ring. Prometheus, e.g. is orbiting on the inner side of the F ring as Pandora is orbiting just on the outer side of it. Pan is orbiting inside the Encke Gap, this small division at the outer part of the A ring as Atlas' orbit is just at the outside edge of the latter. Prometheus is 46 x 31 x 21 miles wide (74 x 50 x 34 kilometers) as it is orbiting Saturn in 1 day 1/3. The moon is seen at the forefront of the F ring. This view is due to the NASA/ESA/Italian Space Agency Cassini-Huygens mission which has begun a 4-year work in orbit around Saturn. picture courtesy NASA/JPL/Space Science Institute