A Shepherding Moon at Saturn. At gas giants, some minor moons are associated with the ring systems like e.g. at Jupiter where four small moons are generating the faint Jupiter rings due to permanent impacts by micrometeoroids. At Saturn, which is the real ringed planet, such minor moons are better shepherding some rings or some part of them. Seen here is Prometheus, a 63-mile (102 km) wide moon. It's orbiting just inside the external and faint Saturnian ring, the F-ring. Other such small moons are seen in the ring, or the vicinity of it. Pan is amusingly orbiting just inside the famous Encke Gap. Or tiny Atlas is orbiting just at the outer limit of the A-ring. On the other hand, Epimetheus e.g. is participating with Prometheus to the organization of the F-ring. Most of these moons are ranging from 6.2 to 59 miles (10 to 95 km) in diameter. Some more such minor moons have been found and might still be by the NASA/ESA/Italian Space Agency Cassini-Huygens mission which began working in orbit around Saturn late July and is preparing for a comprehensive study there. picture courtesy NASA/JPL/Space Science Institute