Local N-Body Simulations for the Rotation Rates of Particles in Planetary Rings

Using N-body simulations, we examine rotation rates caused by mutual collisions of particles in planetary rings. In the case of particles with a power-law size distribution, we find that the size-dependence of the rms rotation rates can be well approximated by a power law. The overall rotation rates increase for a smaller tangential coefficient of restitution, an increased size of the largest particles, and/or a shallower size distribution of particles. However, the slope of the size dependence of the rotation rates is rather insensitive to these parameter values. This size dependence of the particles' rotation rates needs to be taken into account when developing energy balance models that are used to interpret observations of thermal emission from Saturn's rings.