Implementing sub-resolution porosity in a 3D SPH hydrocode. Numerical simulations of impacts involving porous bodies. Simulations of brittle solids using smooth particle hydrodynamics. Dynamical evolution of the Prometheus–Pandora system. First-order resonance overlap and the stability of close two-planet systems. The resonance overlap criterion and the onset of stochastic behavior in the restricted three-body problem. The shape and structure of cometary nuclei as a result of low velocity collisions. Shapes of the saturnian icy satellites and their significance. Cassini Imaging Science: Initial results on Phoebe and Iapetus. Formation of regular satellites from ancient massive rings in the Solar System. Saturn’s F ring and shepherd satellites a natural outcome of satellite system formation. The recent formation of Saturn’s moonlets from viscous spreading of the main rings. Saturn’s small inner satellites: clues to their origins. The equatorial ridges of Pan and Atlas: terminal accretionary ornaments? Science 318, 1622–1624 (2007). Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission. Finally, we show that this mechanism may also explain the formation of Iapetus’ equatorial ridge 7, as well as its oblate shape 8. 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 4, 5, 6. With slightly more oblique impact angles, collisions lead to elongated, Prometheus-like shapes. Close to head-on mergers result in flattened objects with large equatorial ridges, as observed on Atlas and Pan. 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. 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. Closest to Saturn, these bodies provide important clues regarding the formation process of small moons in close orbits around their host planet 4, but their range of irregular shapes has not been explained yet. The Cassini spacecraft revealed the spectacular, highly irregular shapes of the small inner moons of Saturn 1, ranging from the unique 'ravioli-like' forms of Pan and Atlas 2, 3 to the highly elongated structure of Prometheus.
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