Olivine-rich exposures at Bellicia and Arruntia craters on (4) Vesta from Dawn FC

TL;DR

This study uses Dawn FC data to identify and map olivine-rich exposures on Vesta, confirming their presence and distribution, and providing new spectral analysis methods for detecting high-olivine content sites.

Contribution

The paper introduces a novel spectral band parameter combination that reliably identifies olivine-rich areas with over 40% olivine content using Dawn FC data.

Findings

Olivine-rich exposures are confirmed at Bellicia and Arruntia craters.

New spectral parameters enable detection of sites with >40% olivine.

Olivine exposures are mainly located on crater walls, floors, and ejecta in the northern hemisphere.

Abstract

We present an analysis of the olivine-rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine-rich materials at these localities as described by Ammannito et al. (2013a) using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various Howardite-Eucrite-Diogenite meteorites, high-Ca pyroxenes, olivines and olivine-orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine-rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine-rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine-rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake 1997; Yamaguchi et al. 1997). However, it remains unsolved why the olivine-rich materials are mainly concentrated in the northern hemisphere (~36-42{\deg} N, 46-74{\deg} E) and are almost absent in the Rheasilvia basin.