Investigating tidal stripping of a pre-existing moon as the origin of Saturn's young icy rings

TL;DR

This study uses hydrodynamic simulations to explore how a close encounter with Saturn could have tidally stripped a pre-existing moon, forming the planet's young, icy rings with specific mass and composition.

Contribution

It provides the first detailed simulation-based evidence supporting the hypothesis that Saturn's rings originated from tidal disruption of a differentiated moon during a close encounter.

Findings

Preferential tidal stripping of ice can produce rings matching current mass and composition.

Multiple close encounters increase tidal stripping efficiency.

Rocky remnants are removed within a few thousand years after disruption.

Abstract

The origin of Saturn's rings has been debated for decades. Measurements from Voyager and Cassini have suggested that the rings could be as young as ~100 Myr and composed of nearly pure water ice. Several scenarios have been proposed to explain these properties. One hypothesis (Wisdom et al 2022) is that the rings formed through the recent tidal disruption of a pre-existing moon, Chrysalis, which experienced a close encounter with Saturn following its highly eccentric orbit. However, the mechanism by which this hypothesis would have formed the rings remains largely unexplored, in particular, whether Chrysalis could supply ring material of the desired mass and composition. To address these questions, we perform smoothed particle hydrodynamics simulations to investigate the tidal response of Chrysalis during close encounters with Saturn. Our results demonstrate that preferential tidal stripping of the ice mantle from a differentiated Chrysalis can produce rings with both mass and composition resembling the present rings -- provided that the closest encounter occurs between the parabolic Roche limits for ice ~1.53Rs and rock ~1.07Rs -- consistent with Wisdom et al 2022. Moreover, multiple close encounters can extend the effective disruption limit by spinning up the body, enhancing the tidal stripping efficiency. Following close encounters, the rocky remnant of Chrysalis would have been removed in less than few kyr, either by collision with Saturn or ejection onto a hyperbolic orbit. These findings support the hypothesis that Saturn's rings could originate from a recent lost moon, and imply a highly dynamical evolution of the Saturnian system over the past few hundred million years.