LAUSR

Gas Giant Planets During the final stages of the Cassini mission, the spacecraft flew between the planet and its rings, providing a new view on this spectacular system (see the Perspective by Ida). Setting the scene, Spilker reviews the numerous discoveries made using Cassini during the 13 years it spent orbiting Saturn. Iess et al. measured the gravitational pull on Cassini, separating the contributions from the planet and the rings. This allowed them to determine the interior structure of Saturn and the mass of its rings. Buratti et al. present observations of five small moons located in and around the rings. The moons each have distinctive shapes and compositions, owing to accretion of ring material. Tiscareno et al. observed the rings directly at close range, finding complex features sculpted by the gravitational interactions between moons and ring particles. Together, these results show that Saturn's rings are substantially younger than the planet itself and constrain models of their origin. Science , this issue p. [1046][1], p. [eaat2965][2] , p. [eaat2349][3], p. [eaau1017][4]; see also p. [1028][5] [1]: /lookup/doi/10.1126/science.aat3760 [2]: /lookup/doi/10.1126/science.aat2965 [3]: /lookup/doi/10.1126/science.aat2349 [4]: /lookup/doi/10.1126/science.aau1017 [5]: /lookup/doi/10.1126/science.aaw3098