First disk-resolved spectroscopy of (4) Vesta

TL;DR

This study presents the first disk-resolved near-infrared spectroscopic observations of asteroid Vesta, revealing surface compositional variations and linking specific regions to meteorite types, providing insights ahead of the 2011 NASA Dawn mission.

Contribution

It provides the first ground-based disk-resolved spectroscopic data of Vesta, showing surface heterogeneity and correlating spectral features with meteorite analogs.

Findings

Spectral variations suggest compositional or aging differences across Vesta's surface.

Most of Vesta's surface matches the composition of howardite meteorites.

A small diogenite-rich area was identified near 180° East longitude.

Abstract

Vesta, the second largest Main Belt asteroid, will be the first to be explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated body with spectrum suggesting that is has been resurfaced by basaltic lava flows, not too different from the lunar maria. Here we present the first disk-resolved spectroscopic observations of an asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive optics equipped integral-field near-infrared spectrograph SINFONI, as part of its science verification campaign. The highest spatial resolution of ~90 km on Vesta's surface was obtained during excellent seeing conditions (0.5") in October 2004. We observe spectral variations across Vesta's surface that can be interpreted as variations of either the pyroxene composition, or the effect of surface aging. We compare Vesta's 2 micron absorption band to that of howardite-eucrite-diogenite (HED) meteorites that are thought to originate from Vesta, and establish particular links between specific regions and HED subclasses. The overallcomposition is found to be mostly compatible with howardite meteorites, although a small area around 180 deg. East longitude could be attributed to a diogenite-rich spot. We finally focus our spectral analysis on the characteristics of Vesta's bright and dark regions as seen from Hubble Space Telescope's visible and Keck-II's near-infrared images.