Space weathering on Vesta: Ion bombardment induced changes on HEDs in visible and infrared reflectance

Abstract

The NASA/Dawn mission targeted V-type asteroid (4) Vesta between 2011 and 2012. The mission confirmed Vesta as the parent body of most of the HED meteorite family and led an extensive mapping of the surface's spectral properties. The well-pronounced different spectroscopic features of Vesta suggest that this body has its own form of space weathering. In this work, we look for the optimal parameter space for distinguishing between fresh and weathered materials on Vesta and other V-type objects. We emulated the effects of the solar wind component of space weathering by performing ion bombardment experiments with 40 keV He+ on four HED meteorites. We then studied the spectral behavior of our artificially weathered samples, spanning from the visible to the mid-infrared range, using several spectral parameters. We observed that in the visible and near-IR range, the evolution of eight parameters – darkening of reflectance at 380–465-550 nm, decrease in band depth and band area of the 1-μm absorption feature, and reddening of three different spectral slopes - are enough to distinguish between differences in mineral composition and weathering state among our samples. In the mid-IR, we detected a consistent red shift in the position of the Reststrahlen feature, associated with sample weathering. These findings can provide support for the interpretation of remote sensing data from V-type objects, aiding in the assessment of mineralogical differences and the weathering state of surface materials.