Mineralogical characterization of some V-type asteroids, in support of the NASA Dawn mission★

Abstract

We present new reflectance spectra of 12 V-type asteroids obtained at the 3.6 m Telescopio Nazionale Galileo (TNG) covering the spectral range 0.7 to 2.5 μm. This spectral range, encompassing the 1 and 2 μm, pyroxene features, allows a precise mineralogical characterization of the asteroids. The spectra of these asteroids are examined and compared to spectra for the Howardite, Eucrite and Diogenite (HED) meteorites, of which Vesta is believed to be the parent body. The observed objects were selected from different dynamical populations with the aim to verify if there exist spectral parameters that can shed light on the origin of the objects. A reassessment of data previously published has also been performed using a new methodology. We derive spectral parameters from NIR spectra to infer mineralogical information of the observed asteroids. The V-type asteroids here discussed show mainly orthopyroxene mineralogy although some of them seem to have a mineralogical composition containing cations that are smaller than Mg cations. Most of the observed Vestoids show a low abundance of Ca (<10 per cent Wo). This result implies that no one of the Vestoids studied consists of just eucritic material, but they must additionally have a diogenitic component. However, we must remember that the ground-based data are subject to larger errors than the laboratory data used as reference spectra for interpretation. Finally, we note that the intermediate belt asteroid (21238) 1995WV7 has spectral parameters quite different from the observed V-type objects of the inner belt, so it could be a basaltic asteroid not related to Vesta. This mineralogical analysis of asteroids related to Vesta is done in support of NASA’s Dawn mission, which will enter into orbit around Vesta in the summer of 2011. This work extends the scientific context of the mission to include processes contributing to the nature of smaller V-type asteroids that may be related to Vesta.