Can Formulas Derived From Pyroxenes and/or HEDs Be Used to Determine the Mineralogies of V-Type Asteroids?

Abstract

We compare methods for determining the pyroxene mineralogies of V-type near-Earth asteroids from their reflectance spectra. We evaluate whether band centers derived from the spectra of synthetic pyroxenes can be used to achieve greater analytical accuracy than is achieved through the use of band centers derived from the spectra of basaltic achondrites (howardites, eucrites, diogenites or HEDs). We conclude that band centers derived from the reflectance spectra of synthetic pyroxenes with known mineralogies do not provide useful diagnostic information to derive equations for determining accurate pyroxene compositions of V-type asteroids. Band centers from the reflectance spectra of HEDs with known pyroxene mineralogies can be used to derive equations for determining accurate pyroxene compositions of V-type asteroids. HEDs are physical mixtures of a number of different types of pyroxenes and best simulate the surfaces of V-type asteroids. Formulas using the Band I center appear best for determining asteroid pyroxene mineralogies for V-type asteroids due to the current difficulty in doing accurate temperature corrections to the Band II center. Most of the observed V-type near-Earth asteroids have interpreted mineralogies similar to eucrites or howardites. One of the observed near-Earth asteroids could possibly have a surface mineralogy similar to diogenites.