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S. J. Bus (Univ. Hawaii), J. M. Sunshine (SAIC), R. P. Binzel (Obs. Paris), T. H. Burbine (NMNH)
The spectral characteristics of asteroids having a strong 1 um absorption feature are attributed to the presence of pyroxene, olivine, or both. Distinguishing between pyroxene and olivine requires measuring the strength of an additional absorption band centered near 2 um. Accurate measurements of both bands are now possible using SpeX, a new generation low- to medium-resolution infrared spectrograph in operation as a facility instrument at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii.
Visible-wavelength surveys such as SMASSII (Bus 1999; Ph. D. thesis) show a continuum of properties in terms of spectral slope and the depth of the 1 um band, as measured over the wavelength interval 0.4-1.0 um. With SpeX, we are now examining whether this apparent continuum is also evident within spectra extending out to 2.5 um. Taking advantage of our ability to infer mineralogy based on near-infrared spectral information, we are also seeking to understand the extent to which this spectral continuum is rooted in a smooth gradient in olivine-pyroxene mineralogy. We are estimating olivine-pyroxene ratios using the Modified Gaussian Model (MGM) of Sunshine et al. (1990, JGR 95, 6955).