Modelling the disruption and reaccumulation of Miranda

The heavily cratered surfaces of the largest Uranian satellites and the unusual surface geology of Miranda suggest that Miranda could have been catastrophically disrupted by collision and then reaccumulated over solar system history (Smith et al., 1986; Mckinnon et al., 1991). Using the numerical model described by Marzari et al. (1995) we have simulated the breakup of Miranda by a high velocity impact and computed the size and orbital distributions of the collisional fragments. These distributions have been adopted as realistic initial conditions for the numerical algorithm of Spaute et al. (1991) with which we have simulated the reaccumulation of the satellite from the ring of debris. Our results show that the reaccumulation of Miranda occurs on a short timescale ( ~ 10(3) years), in spite of the initial large dispersion 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 in accretion, the reaccumulation of Miranda proceeds as an orderly growth with larger bodies accreting mass from the smaller ones. If cratering 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 stage the large surviving fragments grow by accumulating the small comminuted fragments and finally, colliding with each other, re-build a new Miranda. Different breakup reaccumulation scenarios have been analyzed to account for the variation of some physical parameters.