NUMERICAL SIMULATIONS OF DENSE COLLISIONAL SYSTEMS

Viscous stability properties of dense planetary rings are examined with a local simulation method closely resembling that of Wisdom and Tremaine (1988, Astron. J. 95, 925). We confirm their result that for the standard elastic model of icy particles the viscous instability is not expected to occur for systems consisting of identical meter-sized particles. Our results suggest, however, that in principle it could take place in dense systems of centimeter-sized particles, as well as in the case of "harder" particles than described with the standard elasticity model. Also, in the case of nonidentical particles, small particles are shown to become more easily unstable. Simulation with self-gravity confirm the layered vertical structure observed by Wisdom and Tremaine, although the detailed structure is significantly modified if the vertical field is calculated self-consistently, or if unequal particle sizes are taken into account. In some cases, almost complete flattening to central plane is observed. © 1991.