A preliminary global geologic map of Vesta based on Dawn Survey orbit data

NASA's Dawn spacecraft arrived at the asteroid 4Vesta on July 15, 2011, and is now collecting imaging, spectroscopic, and elemental abundance data during its one-year orbital mission. As part of the geological analysis of the surface, we have utilized images and data from the Survey orbital sequence to produce a global map of Vesta's surface. Unit boundaries and feature characteristics were determined primarily from morphologic analysis of image data; projected Framing Camera (FC) images were used as the base map. Spectral information from FC and VIR are used to refine unit contacts and to separate compositional distinctions from differences arising from illumination or other factors. Those units that could be discerned both in morphology and in the color data were interpreted as geologically distinct units. Vesta's surface is highly-cratered; differences in color and albedo are possible indicators of varying thicknesses and areal extents of crater ejecta. The most prominent candidate impact feature dominates the south pole. This feature consists of a depression roughly circular in shape, with a central hill that is characterized by smoother texture and lower albedo distinctive from the lower-lying surrounding terrain. A complex network of deep troughs and ridges cuts through the floor of the feature. Many of these troughs trend north-south, while others appear circumferential to the hill and are truncated by or terminate at orthogonal ridges/grooves. Detailed mapping of these features will provide information on their orientations, possible origin(s), and their relationship, if any, to the central hill. The equator of Vesta is also girdled by a wide set of flat-floored troughs. Their orientation implies that their formation is related to the south polar structure. Several regions on Vesta have a concentration of craters displaying low-albedo interiors or exteriors. These craters may have an exogenic origin, or may be the result of excavation of a thin sub-surface layer. Low-albedo regions also appear to have been uncovered by mass wasting around some topographic highs. If this dark material is endogenic in origin, this suggests that Vesta has both vertical and lateral stratigraphic heterogeneity. Current imaging also reveals dark materials and smooth regions that may be candidate locations/sites for volcanic activity. Further study at greater spatial and spectral resolution is required to unequivocally identify the character and origin of these features. The authors gratefully acknowledge the support of the Dawn Operations, Instruments, and Science Teams.