Formation of Saturn's Rings by Tidal Disruption of a Centaur

Planetary rings owe their existence to tidal forces, which frustrate accretion into larger bodies. Models for ring origin include (a) formation in situ, (b) disruption of a moon by cometary impact, and (c) tidal disruption of an interloping Centaur ([1]). [2] applied model (c) to Saturn's rings, basing his results on analytic expressions and taking Chiron to be a typical Saturn-crosser. Many Saturn-crossers have now been discovered, and our understanding of tidal disruption has advanced, particularly through models of the breakup of Comet Shoemaker-Levy 9 (SL9). [3] treated SL9 as a rubble pile, and modeled its disruption with a fast N-body code that included self-gravity and a simple model of collisions. We are using a modified version of this code to follow the tidal disruption of model Centaurs that pass within Saturn's Roche radius. Our simulations have four free parameters: the Centaur's approach velocity to Saturn (v), closest approach distance to Saturn (q), size (r), and rotation state. Mass capture is favored for events with small v and q, large r, and fast direct rotation ([4]). We will estimate the rate of ring formation by tidal disruption, and will constrain the heliocentric orbits of plausible ring parent bodies. Saturn's B Ring may be much more massive than was previously thought ([5],[6]). We will discuss the implications of a more massive ring system for different origin scenarios. We thank the NASA PGG program for support.

[1] Pollack JB 1975. Space Sci. Rev. 18, 3. [2]Dones L 1991. Icarus 92, 194.

[3] Asphaug E; Benz W 1996. Icarus 121, 225. [4] Richardson DC; Bottke WF; Love SG 1998. Icarus 134, 47.

[5] Robbins SJ; Stewart GR; Colwell JE; Lewis MC 2007. DPS meeting 39, abstract 7.05. [6] Stewart GR; Robbins SJ; Colwell JE 2007. DPS meeting 39, abstract 7.06.