Physical Characterization of the Vesta Family Asteroids

A photometric survey has been undertaken of the Vesta asteroid family in order to gain a better understanding of its collisional origin. The Vesta family members ("chips") are believed to be the result of a subcatastrophic collision that left behind a large impact crater on Vesta's surface. Our primary objective is to determine the large-scale shape characteristics of the fragments from an impact event, and we have focused on a small number of targets for which we could obtain detailed lightcurve information (including rotation rate and pole orientation) during multiple apparitions. We will summarize progress to date. Most of the objects observed have displayed lightcurve characteristics typically associated with tri-axial ellipsoids, but a few have revealed more unusual features. In particular, the lightcurves of 3782 Celle (Ryan et al. 2004a) and 3703 Volkonskaya (Ryan et al. 2004b) are indicative of asynchronous binary systems. Models of these systems have allowed us to estimate bulk densities, and derive preliminary conclusions relevant to satellite formation in cratering impact events. In addition, other targets within this survey have revealed unusual lightcurve features that have the appearance of anomalous attenuations, but with periodicities that appear to be synchronous with the primary's rotation.

This work is supported by the NASA Planetary Astronomy Program and the generous observing time made available by the Vatican Observatory Research Group and NOAO.

References

Ryan, W. H., Ryan, E. V., Martinez, C. T., 2004a; Planet. Space Sci. 52, 1093-1101.

Ryan, W. H., Ryan, E. V., Martinez, C. T., 2004b; Bul. Amer. Astron. Soc. 36, 1181-1182.