Collisional and Dynamical History of Ida

surprisingly steep size distribution, and global jolting by large impacts modifies the cratering record by frequently The history of Ida is constrained by its membership in the Koronis family, its satellite Dactyl, the record of impacts left on erasing smaller craters over the entire surface. Ida differs its surface, and other dynamical, morphological, and spectral from Gaspra in a number of fundamental ways, both in its properties. Models of crater production and comparably effecobservable physical properties and in its setting among tive erasure processes, combined with the current size– impacting populations of smaller bodies. The challenge to frequency distribution of craters, suggest that the age of the interpreters is to develop a scenario for the history of surface is either about 50 myr or .1 byr. The younger age may Ida that accounts for its differences from Gaspra, while be inconsistent with the degraded appearance of many craters, invoking a consistent physical model. while the older age conflicts with the collisional life expectancy The following differences provide critical constraints in of Dactyl. Consideration of Dactyl’s evolution may resolve this developing such a scenario: issue as well as shed light on the formation of Dactyl, the density of Ida, and possible source regions for Ida and Dactyl (a) Ida is much larger than Gaspra (about 56 km long), within the Koronis parent body.  1996 Academic Press, Inc. and even more elongated and irregular in shape (Belton et al. 1994). Impactors of a given size are likely to produce different sized craters on Ida than on Gaspra, and to have