Spectral Variations within the Koronis Family: Possible Implications for the Surface Colors of Asteroid 243 Ida

Abstract

Asteroid 243 Ida, a flyby target for the Galileo spacecraft, is a member of the Koronis family which likely formed from the collisional disruption of a single larger parent body. We investigate the visual spectra of eight of these physically related Koronis family members, including Ida. All are S-class asteroids, but show a range of pyroxene band depths (and band center positions) that may have some correlation with location within the family. If the diversity is attributable to compositional variation, rather than particle size effects, these family members may sample different stratigraphic units from within the parent body's interior. Translated to the 7560- and 9860-Å Galileo filters, the observed spectral diversity corresponds to color variations of about ±5% with respect to Ida's mean color. Such variations may be imaged on Ida if it is a single intact fragment which samples across stratigraphic units or if it is a conglomerate object composed of samples from multiple units.