MODELING THE DISRUPTION AND REACCUMULATION OF MIRANDA

The heavily cratered surfaces of the largest Uranian satellites and th e unusual surface geology of Miranda suggest that Miranda could have b een catastrophically disrupted by collision and then reaccumulated ove r solar system history (Smith et al., 1986; Mckinnon et al., 1991). Us ing the numerical model described by Marzari et al. (1995) we have sim ulated the breakup of Miranda by a high Velocity impact and computed t he size and orbital distributions of the collisional fragments. These distributions have been adopted as realistic initial conditions for th e numerical algorithm of Spaute et al. (1991) with which we have simul ated the reaccumulation of the satellite from the ring of debris. Our results show that the reaccumulation of Miranda occurs on a short time scale (similar to 10(3) years), in spite of the initial large dispersi on of the ring debris and the presence of Ariel at the outer border of the ring. However the reaccumulation process depends strongly on the poorly known outcomes of collisions. If collisions dominately result i n accretion, the reaccumulation of Miranda proceeds as an orderly grow th with larger bodies accreting mass from the smaller ones. If crateri ng and fragmentation are included, the reaccumulation is characterized by two stages: an initial stage during which shattering dominates and all bodies smaller than few tens km are destroyed. In the second stag e the large surviving fragments grow by accumulating the small comminu ted fragments and finally colliding with each other, rebuild a new Mir anda. Different breakup reaccumulation scenarios have been analyzed to account for the variation of some physical parameters.