Constraints on the initial mass, age and lifetime of Saturn's rings from viscous evolutions that include pollution and transport due to micrometeoroid bombardment

Abstract

The Cassini spacecraft provided key measurements during its more than twelve year mission that constrain the absolute age of Saturn's rings. These include the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and a measurement of the ring mass. These observations taken together limit the ring exposure age to be < a few 100 Myr if the flux was persistent over that time (Kempf et al., 2023). In addition, Cassini observations during the Grand Finale further indicate the rings are losing mass (Hsu et al., 2018; Waite et al., 2018) suggesting the rings are ephemeral as well. In a companion paper (Durisen and Estrada, 2023), we show that the effects of micrometeoroid bombardment and ballistic transport of their impact ejecta can account for these loss rates for reasonable parameter choices. In this paper, we conduct numerical simulations of an evolving ring in a systematic way in order to determine initial conditions that are consistent with these observations.