THE FORMATION AND COLLISIONAL DYNAMICAL EVOLUTION OF THE IDA DACTYL SYSTEM AS PART OF THE KORONIS FAMILY/

The Ida/Dactyl system is the first confirmed asteroid/satellite pair a s well as the first family asteroid to be studied in detail by a space craft. We explore consequences for Ida of formation by disruption of t he Koronis parent body. A significant flux of projectiles onto Ida in a few years following the formation of the family is found, based on m odels of the disruption of the Koronis parent body by Marzari et al. ( Marzari, F., D. Davis, and V. Vanzani 1995. Icarus 113, 168-187). This flux generated craters at a rate much higher than the current crater production rate; however, the flux decreases rapidly as fragment orbit s become randomized. Also, we compare the figure of Ida with figures o f equilibrium fluid bodies and find that the interior of Ida is nearly stress-free and that Ida could be a rubble pile. Finally, collisional models predict that Dactyl would have been shattered several times in the past 2 billion years, the lower bound on Ida's age derived from i ts cratered surface. However, some of the ejecta from such disruptions would be trapped in orbit about Ida, subsequently reaccumulating into a satellite. This process could explain the rather regular shape of D actyl as well as explaining how Dactyl now exists, given its short (co mpared with Ida's age) collisional disruption lifetime. (C) 1996 Acade mic Press, Inc.