GEOLOGIC MAPPING FOR SMALL ROCKY BODIES: THE VESTA EXAMPLE

Defining criteria for mapping the boundaries of material units on airless, rocky bodies is challenging. Where the primary geologic process for the bulk of a small body’s history is impact cratering, the traditional mapping approach of using morphology as the primary criterion of unit definition can be problematic, because the differences in morphological characteristics among the various cratered surfaces can be subtle to absent, and surface morphology is muted by the regolith’s physical and mechanical properties. In constructing a global geologic map of Vesta at 1:300,000-scale using the Dawn Framing Camera (FC), DTM-derived slope and contour, and color (visible wavelength) and spectroscopic data, we have been evaluating how much weight each dataset should be given in defining criteria for unit boundaries, and what the consequences of those choices are.

Our initial approach was to characterize units based on morphology, surface textures, and albedo, as well as crater size-frequency distribution and superposition relations. Color data from the FC (and VIR) were examined as an overlay on the first draft of units, to refine unit boundaries where morphologic characteristics provided more than one possible border, or the interpretation of the unit type was ambiguous. However, this method did not provide us with sufficient ability to assess and interpret the spectroscopic and color data on its own merits. As a result, the color and morphologic data were not being incorporated synergistically into interpretations.

Recently we have begun a different approach, one initially used to test how the availability of various types of datasets affects mapping results. This method requires creating a GIS map based on each available dataset in isolation, then comparing the resulting maps to assess the information unique to each dataset, and of that, what best summarizes the geologic history of the region. We report on initial results of this approach.