Saturn's rings are young — about 100 million years old, based on Cassini data — and nearly pure water ice. This combination demands an explanation: what process could produce massive ice rings recently, leaving almost no rocky contamination?
Jiao, Nimmo, Wisdom, and Dbouk simulate the tidal stripping of Chrysalis, a hypothetical differentiated moon. As Chrysalis passes within Saturn's Roche limit, tidal forces preferentially strip the ice mantle while the rocky core remains gravitationally bound. The ice goes into orbit to become the rings. The core, now unshielded, is removed within a few thousand years — either colliding with Saturn or ejected onto a hyperbolic orbit.
The key is differentiation. An undifferentiated moon would produce rings contaminated with rock. A differentiated moon — ice mantle over rocky core — allows selective stripping because the ice sits at the surface where tidal stresses are strongest. Multiple close approaches enhance the effect through rotational excitation of the moon, allowing progressive mantle removal across successive encounters.
The result matches both the mass and the composition of the present rings within specific orbital parameters. The mechanism requires the encounter to be close enough for tidal stripping but not so close that the entire moon is destroyed — a parameter window that the simulations map quantitatively.
Saturn's rings are the remnant skin of a dead moon, shed in weeks and dispersed into orbit. The rocky interior was swallowed. Only the ice survived.