Olivine or Impact Melt: Nature of the "Orange" Material on Vesta from Dawn

TL;DR

This study characterizes the orange material on Vesta, revealing it to be impact melt based on multi-instrument analysis of its spectral, compositional, and geomorphological features.

Contribution

It provides a detailed classification and analysis of Vesta's orange material, identifying it as impact melt through integrated remote sensing data.

Findings

Orange material is concentrated outside Rheasilvia basin.

The material includes diffuse ejecta, lobate patches, and ejecta rays.

Impact melt is the most probable composition of the orange material.

Abstract

NASA's Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types, a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), b) lobate patches with well-defined edges, and c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed "Leslie feature" first identified by Gaffey (1997) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt.