Formation of the Cassini Division - I. Shaping the rings by Mimas inward migration

Abstract

In 2017, the Cassini mission Grand Finale provided hints at the total mass of Saturn's ring system, constraining the age of the rings: they could actually be about 200 million years old or even younger. However, the present radial mass distribution across the rings is not well understood. The most prominent structure, visible from Earth, is the Cassini Division, a 4500 km-wide gap that separates the massive inner B ring and the outer A ring. Though early models of the formation of the Cassini Division suggested that the resonant interaction of ring particles with the external satellite Mimas (Lindblad resonance 2:1) could open a significant gap (slightly narrower than the observed Cassini Division) in 5 billion years, we investigate here an alternative scenario involvingmuch shorter time-scales based on the newconstraints on the age of the rings. In this article, we present a numerical model of satellite-ring interactions that can explain the formation of the Cassini Division by the orbital migration of Mimas and the different densities of the current A and B rings. Such a scenario implies that the Cassini Division could have opened in the last 4-11 million years and that it might disappear in the next 40 million years from now.