We present the preliminary results of the application of linear unmixing techniques to several main belt asteroid spectra in an effort to estimate the abundances of the substances present on their surface. Depending on the level of non-linear scattering behavior due to fine particulate regolith, observed asteroid spectra can be reconstructed reasonably well using linear combinations of the spectra of the components the surface is comprised of. Using laboratory endmember spectra from the RELAB database, we employ Markov Chain Monte Carlo methods to determine the best fit combination of surface components that reproduce existing visible and NIR asteroid spectra, which were obtained from the 8 and 52 color asteroid surveys respectively. As a proof of concept, we work specifically with a subset of endmembers that are shown to reproduce S-type asteroid spectra reasonably well by Clark (1995) and use her abundance estimates as a comparison point. We apply our techniques to several S-type asteroids, testing both fully constrained and unconstrained models to see how derived abundances differ, noting that unconstrained models are likely more physically plausible and allow for unknown spectral components. We aim to develop a technique that can easily estimate asteroid surface abundances from their spectra and correlate them with other more readily obtainable measurements, such as NIR albedos derived from NEOWISE. It has been shown that some asteroid families tend to clump around specific values in NIR albedo space, identified in Masiero et al. (2014), a trend that could be further explained by differences in surface abundances between those families. The results presented here serve as a first step towards determining what the connection might be between NIR albedo and surface composition and may allow for NIR albedo to be used in the future as a diagnostic for composition, acting as a tool for the quick characterization of known asteroids and NEOs as well as those not yet discovered.
Clark, B. E. 1995. Spectral mixing models of S-type asteroids. Journal of Geophysical Research 100, 14443.
Masiero, Joseph R., et al. “Main-belt asteroids with WISE/NEOWISE: Near-infrared albedos.” The Astrophysical Journal 791.2 (2014): 121.