The geologic time scale of asteroid Vesta derived from geologic mapping. From Williams et al. (2014). The uncertainty in the model age dates stems from the uncertainty of the flux of impacting small asteroids. Ga = billions of years ago.
JPL manages the Dawn mission for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. The University of California, Los Angeles (UCLA) is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team.
More information about Dawn is online at http://www.nasa.gov/dawn.