The origin and evolution of the Uranian dust rings

The numerous dust bands discovered by Voyager 2 at Uranus have lifetimes on the order of 100 years against orbital decay by exospheric drag. A system of low optical depth rings of 10 meter to 1 km sized bodies (moonlet belts) are proposed as continuing sources of the dust particles.;The ring system is modeled as a Markov Chain consisting of states through which dust particles evolve with time. Physical processes included in the model are orbit decay by exospheric drag and Poynting-Robertson light drag; destruction of grains by meteoroid impact; transport of dust through the classical rings and moonlet belts; creation of dust particles from meteoroid impacts onto rings, moons, and moonlet belts; liberation of regolith material through ring and moonlet belt particle collisions; and sweepup of ejecta by ring and moonlet belt particles. The optical depth profiles for the main rings from Voyager 2 Photopolarimeter Subsystem (PPS) occultation observations are used in modeling the transport of dust through the rings. In addition, a statistical analysis of the PPS data show that some of the Uranian rings are azimuthally inhomogeneous similar to the clumpy ring of Neptune, 1989N1R, and the F Ring of Saturn.;Simulations of the Uranus ring system show that this model reproduces the observed characteristics of the Uranus dust rings. The moonlet belt model is applied to the rings of Jupiter, Saturn, and Neptune, and is capable of reproducing some of the observed characteristics of those ring systems. The moonlet belt objects fit on a collisionally derived power-law size distribution with the other components of the ring moon system. Since the rings and moonlet belts have lifetimes due to viscous spreading less than the age of the solar system, a new model of planetary rings emerges in which the rings are continually created from the disruption of small satellites by meteoroid bombardment. Thus, planetary rings are continually created and destroyed over the age of the solar system in this model and are not relics left over from the formation of the planets.