Saturn’s ridged moons may have gotten their weird shapes from a moonlet demolition derby. The small inner moons have a range of strange shapes: Pan and Atlas are disks with bulging middles like ravioli, Prometheus is elongated like a cigar, and others look like misshapen potatoes. They may have formed when pairs of smaller moonlets crashed into one another and merged.

To figure out whether mergers are a plausible explanation for Saturn’s menagerie of moons, Adrien Leleu at the …