The Age and Origin of Saturn’s Rings

Abstract The origin of Saturn’s rings is a long standing mystery in planetary science, for which the age of this system is a critical constraint. After having clarified what the age of the rings may mean, this article reviews several aspects of this question. We discuss the exposure age, which was recently found to be on the order a few 100 Myrs based on the rings’ composition and their bombardment rate by micrometeoroids. The derivation of this age is explained, and the possible caveats are discussed, including the idea of a putative phenomenon of cleaning of the rings. We address the age of structures such as the Cassini division, plateaux, ramps, and how they are constrained by interactions with satellites and the effects of bombardment. We then address the dynamical evolution of the rings, due to viscosity, micrometeoroid bombardment, and satellite torques. Initially massive rings are found to viscously spread and lose mass quickly and then converge to the present mass in billions of years. However, the dynamical effects of micrometeoroid bombardment can take the reins over viscosity and may wipe the rings out efficiently. Naturally, consideration of ring origin also motivates us to review the ring formation models existing in the literature, and discuss their implications on the composition and age of the rings, in particular in the frame of large tidal dissipation inside Saturn. Finally, putting together and synthesizing these results, we conclude that a fully consistent picture for the origin and age of Saturn’s rings has yet to be established and more work remains to be done to resolve this important question.