  The Cassini spacecraft revealed the spectacular, highly irregular shapes of
the small inner moons of Saturn, ranging from the unique "ravioli-like" forms
of Pan and Atlas to the highly elongated structure of Prometheus. Closest to
Saturn, these bodies provide important clues regarding the formation process of
small moons in close orbits around their host planet, but their range of
irregular shapes has not been explained yet. Here we show that the spectrum of
shapes among Saturn's small moons is a natural outcome of merging collisions
among similar-sized moonlets possessing physical properties and orbits that are
consistent with those of the current moons. A significant fraction of such
merging collisions take place either at the first encounter or after 1-2
hit-and-run events, with impact velocities in the range of 1-5 times the mutual
escape velocity. Close to head-on mergers result in flattened objects with
large equatorial ridges, as observed on Atlas and Pan. With slightly more
oblique impact angles, collisions lead to elongated, Prometheus-like shapes.
These results suggest that the current forms of the small moons provide direct
evidence of the processes at the final stages of their formation, involving
pairwise encounters of moonlets of comparable size. Finally, we show that this
mechanism may also explain the formation of Iapetus' equatorial ridge, as well
as its oblate shape.
