DAWN COMPLETES ITS MAPPING OF VESTA: AN INTRODUCTION TO DAWN'S FINDINGS (Invited Presentation)

The Dawn spacecraft slipped into orbit about Vesta on July 16, 2011, and successfully executed four mapping phases at 3000 km (Survey), 900 km (High Altitude Mapping Orbits 1 and 2), and 475 km (Low Altitude Mapping Orbit) planetocentric radii before leaving Vesta’s gravitational field on August 26, 2012. The identification of Vesta as the parent body of the Howardite-Eucrite-Diogenite meteorites and the confirmation of this identification by the initial observations of Vesta’s geochemistry, geology, and internal structure enabled rapid understanding of Vesta’s origin, evolution and current physical properties. Collisions have played a major role in shaping Vesta as well as liberating vestoids and the HED meteorites that have informed us so well. Earlier remote observations with HST and Earth-based telescopes of diverse mineral composition have been confirmed and enhanced by the high-resolution data provided by Dawn, although we have not yet confirmed purported olivine detections. Geochemical studies of the HEDs have been complemented by geologic contextual information. In particular, the excavated Rheasilvia basin has provided such context for the diogenite meteorites. High-resolution imagery provided geologic details not available from 1 AU such as: the existence of troughs (fossa) associated with major impacts; the distribution of bright and dark material across the surface indicative of exogenic supply of carbon and hydrogen bearing minerals to Vesta; and pitted terrain demonstrating that substantial quantities of volatiles were part of this transport. The cratering record is allowing the chronology of Vesta to be explored and is providing further constraints on the migration of planets and the late heavy bombardment of the inner solar system.