PerspectivePlanetary Science

The origin of Saturn's rings and moons

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Science  14 Jun 2019:
Vol. 364, Issue 6445, pp. 1028-1030
DOI: 10.1126/science.aaw3098

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Saturn's rings consist of vast numbers of small icy particles that frequently collide with each other. Within Saturn's Roche limit (that is, closer to Saturn's center than twice Saturn's physical radius RS), the icy particles disperse and form rings, whereas outside the Roche limit, they grow through pairwise collisions to form moons. The formation of Saturn's rings and moons should thus be closely related. On pages 1054, 1053, and 1052 of this issue, respectively, Tiscareno et al. (1), Buratti et al. (2), and Iess et al. (3) report results from the Cassini mission's ring-grazing orbit and Grand Finale observations, which reveal the detailed structure of the rings and associated moons. The results strongly suggest that Saturn's rings are much younger than Saturn itself and provide important clues to the origin of the rings and moons.