Mineralogic Mapping of the Av-9 Numisia quadrangle of Vesta

In this manuscript we present the mineralogic mapping of the Av-9 Numisia quadrangle of Vesta using the most up-to-date data from the NASA–Dawn mission.

This quadrangle is located in Vesta’s equatorial zone (22°° south to 22°° north, 218°° to 288°° east, in Claudia coordinate system) and takes its name from the impact crater Numisia. The main feature, which dominates the quadrangle, is the Vestalia Terra plateau, a topographic high about 10 km above the surrounding areas. To the south, this region fades into the Rheasilvia basin, while to the north it is bounded by the steep scarp of Postumia basin.

The Visible and Infrared mapping spectrometer (VIR) onboard NASA/Dawn provided the main data source for this work, at an unprecedented level of spatial and spectral resolution. In particular we are using spectral parameters to synthesize characteristics of the whole spectra into a single value. Pyroxene-related spectral parameters allow for the detection of lower crust or mantle material (diogenites) and upper crust material (eucrites) in the study area.

The combined analysis of albedo from the Framing Camera, the geologic map and the spectroscopic data offer an interesting opportunity to understand better the surface features of this region of Vesta, and their evolution.

Numisia, Cornelia, Fabia, Teia and Drusilla are the main craters in the study area, rich in bright and dark material outcrops, pitted terrains and OH-rich materials.

Using the spectral parameters we demonstrate that the internal composition of Vestalia Terra is mainly diogenite-rich howardite, as shown by materials excavated by Cornelia and Fabia, and the composition of the slope north of Vestalia Terra. This agrees with the strong positive Bouguer Anomaly observed in the area, indicating a higher density of these features in relation to the surrounding areas.

Besides the recently published works based on gravimetric modelling and geologic interpretation, the mineralogic mapping presented herein gives an additional contribution, in order to depict a more complete geologic history of the Numisia quadrangle of Vesta.