The peculiar shapes of Saturn’s small inner moons as evidence of mergers of similar-sized moonlets

Leleu, Adrien Sebastien; Jutzi, Martin; Rubin, Martin (2018). The peculiar shapes of Saturn’s small inner moons as evidence of mergers of similar-sized moonlets. Nature astronomy, 2(7), pp. 555-561. Nature Publishing Group 10.1038/s41550-018-0471-7

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The Cassini spacecraft revealed the spectacular, highly irregular shapes of the small inner moons of Saturn1, ranging from the unique 'ravioli-like' forms of Pan and Atlas2,3 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 planet4, 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 size4–6. Finally, we show that this mechanism may also explain the formation of Iapetus’ equatorial ridge7, as well as its oblate shape8.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Leleu, Adrien Sebastien; Jutzi, Martin and Rubin, Martin


500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics




Nature Publishing Group




Dora Ursula Zimmerer

Date Deposited:

23 Jul 2018 15:53

Last Modified:

23 Jul 2018 15:53

Publisher DOI:





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