Two new basaltic asteroids in the Outer Main Belt?

TL;DR

This study reports spectroscopic confirmation of two candidate basaltic asteroids in the outer Main Belt, revealing unique surface mineralogy features and suggesting they are among the few basaltic bodies in that region.

Contribution

First spectroscopic confirmation of two outer Main Belt V-type asteroids with unusual mineralogical features, expanding knowledge of basaltic asteroid distribution.

Findings

Spectra show typical V-type features with a new absorption band at 0.65 microns.

Asteroids (7472) Kumakiri and (10537) 1991 RY16 are likely basaltic, similar to (1459) Magnya.

Presence of a chromium-related absorption feature suggests unique surface mineralogy.

Abstract

The identification of basaltic asteroids in the asteroid Main Belt and the description of their surface mineralogy is necessary to understand the diversity in the collection of basaltic meteorites. Basaltic asteroids can be identified from their visible reflectance spectra and are classified as V-type in the usual taxonomies. In this work, we report visible spectroscopic observations of two candidate V-type asteroids, (7472) Kumakiri and (10537) 1991 RY16, located in the outer Main Belt (a > 2.85 UA). These candidate have been previously identified by Roig and Gil-Hutton (2006, Icarus 183, 411) using the Sloan Digital Sky Survey colors. The spectroscopic observations have been obtained at the Calar Alto Observatory, Spain, during observational runs in November and December 2006. The spectra of these two asteroids show the steep slope shortwards of 0.70 microns and the deep absorption feature longwards of 0.75 microns that are characteristic of V-type asteroids. However, the presence of a shallow but conspicuous absorption band around 0.65 microns opens some questions about the actual mineralogy of these two asteroids. Such band has never been observed before in basaltic asteroids with the intensity we detected it. We discuss the possibility for this shallow absorption feature to be caused by the presence of chromium on the asteroid surface. Our results indicate that, together with (1459) Magnya, asteroids (7472) Kumakiri and (10537) 1991 RY16 may be the only traces of basaltic material found up to now in the outer Main Belt.