oids, their formation, and their evolution. The Galileo data settled the question of the existence of asteroidal satellites
The Ida/Dactyl system is the first confirmed asteroid/satellite pair as well as the first family asteroid to be studied in detail with the discovery of Dactyl (Chapman et al. 1995), the first by a spacecraft. We explore consequences for Ida of formation known asteroidal satellite. Galileo also provided spatially by disruption of the Koronis parent body. A significant flux of resolved images of varying resolution of much of Ida's projectiles onto Ida in a few years following the formation of surface (Belton et al. 1994), allowing inferences to be made the family is found, based on models of the disruption of the about the cratering age and shape of the asteroid. In this Koronis parent body by Marzari et al. (Marzari, F., D. Davis, paper we address the implications for the Ida/Dactyl sysand V. Vanzani 1995. Icarus 113, 168-187). This flux generated tem of their being part of an asteroid family. In particular, craters at a rate much higher than the current crater production we study how the projectile flux that craters an asteroid rate; however, the flux decreases rapidly as fragment orbits surface can be different for a family member than for become randomized. Also, we compare the figure of Ida with a nonfamily asteroid. By identifying how the dynamical figures of equilibrium fluid bodies and find that the interior of Ida is nearly stress-free and that Ida could be a rubble pile. environments of Ida and Gaspra differ, we can better un-Finally, collisional models predict that Dactyl would have been derstand how to interpret crater statistics to infer ages of shattered several times in the past 2 billion years, the lower surfaces. By comparing the best fit ellipsoidal shape of Ida bound on Ida's age derived from its cratered surface. However, with those of equilibrium figures, we find that Ida's interior some of the ejecta from such disruptions would be trapped in is subject to very low stresses; hence it could equally well orbit about Ida, subsequently reaccumulating into a satellite. be a ''rubble pile'' or a single fragment. In addition, we
This process could explain the rather regular shape of Dactyl study the effects of the projectile population on the small as well as explaining how Dactyl now exists, given its short satellite Dactyl and show that it could have been disrupted
(compared with Ida's age) collisional disruption lifetime. ยฉ 1996 and reaccreted in orbit about Ida.
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II. FORMATION AND EVOLUTION OF THE KORONIS FAMILY I. INTRODUCTION
The wealth of data returned by the Galileo spacecraft Asteroid families, identified as statistically significant clusters in orbit element space (Hirayama 1918), are during its brief flyby of asteroid 243 Ida yielded new discoveries and raised a host of new questions regarding aster-thought to be the fragments formed by collisional disrup-220