From The Planetary Society comes this image of Saturn and its moon, Helene. (Several other magnificent color pictures of Saturnian moons at the link.) You can tell at glance it's a fairly small moon; it's irregularly shaped and has enormous relief compared to its size. Larger bodies with more mass are more strongly effected by gravity and pull themselves into more spherical shapes. A quick check of Wikipedia gives its mean diameter as 17.6 km (11 miles). Though this moon was only discovered in 1980, it was not from a Voyager flyby, but from ground-based observations.