A proposed Time-Stratigraphic System for Protoplanet Vesta

(1) Arizona State University, School of Earth & Space Exploration, Tempe, United States (david.williams@asu.edu, 480-965-8102), (2) Inst. of Planetary Research, German Aerospace Center (DLR), Berlin, Germany, (3) Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennesse, USA, (4) NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA, (5) Department of Earth and Space Sciences, UCLA, Los Angeles, California, USA