A Geologic Map of Vesta Produced Using a Hybrid Method for Incorporating Spectroscopic and Morphologic Data

We have constructed a global geologic map of the minor planet Vesta at 1:300,000-scale using Dawn spacecraft imaging, spectroscopic, topographic, and elemental data. In this effort, we used a mapping method that requires creating two maps independently: the first map uses morphology and topography to define map units, while the second map relies on multispectral data (“color”) to define units. The two are then combined into a hybrid product that retains the maximum amount of unique information from both maps in a readable format. This effort has revealed that for bodies where cratering is the dominant unit-forming process, and where there is not a close correlation between morphological feature types and multispectral signal, a hybrid mapping method better retains unique information carried by multispectral data during the mapping process than traditional morphology-based methods alone. Conversely, relying too heavily on color data risks placing too much emphasis on information drawn from the top few microns of the surface. To ensure both consistency and retention of unique information, we created a decision tree for determining which data would be primary in choosing where to draw unit boundaries. Also due to the significant amount of information borne by spectral data, we repurposed traditional mapping nomenclature so that subscripts carry color information. We recommend using this mapping methodology on bodies where (a) morphologic feature boundaries are commonly subtle, gradational, or both, and (b) spectral data carries a significant amount of unique data for identifying, characterizing, and interpreting geologic units.