Exploring Shear-free Ringlet Formation with Direct Simulations of Saturn's B Rings

Abstract

Abstract In this paper, we study the effect of interparticle cohesion in numerical simulations of Saturn’s main rings. Theoretical studies propose that the irregular structure in Saturn’s rings may arise from alternating “solid” and “liquid” ring material. These studies suggest that for sufficiently high interparticle cohesion, shear-free rings around Saturn may form. We use a highly optimized N-body code that models particle self-gravity, soft-sphere collisions, and interparticle cohesion to simulate a patch of Saturn’s rings with periodic boundaries. We present results for nine different cohesion values ranging from 5.0 × 10−2 to 7.0 Pa, dynamical optical depths of 0.8, 1.4, and 1.8, particle material densities of 0.5 and 1 g cm−3, and restitution coefficients of 0.8 and 0.55. Our simulations show a transition of ring particles forming self-gravity wakes to forming structureless uniform distributions of smaller and faster-moving clumps as cohesion increases. The transition from wakes to structureless form occurs at lower inner-particle cohesion values for higher dynamical optical depth. We present an analysis of the physical optical depth, particle number density, and structure characteristics in the simulations at equilibrium. For high cohesion values, energy injection from differential shear causes transient large structures to rotate and collide at high speed, breaking them apart, ultimately limiting the clump size and frustrating the formation of shear-free zones.