Observational and Data Reduction Techniques to Optimize Mineralogical Characterizations of Asteroid Surface Materials

Introduction: Mineralogy is the key to determining the compositional history of the asteroids and to determining the genetic relationships between the asteroids and meteorites. The most sophisticated remote mineralogical characterizations involve the quantitative extraction of specific diagnostic parameters from reflectance spectra and the use of quantitative interpre-tive calibrations to determine the presence, abundance and/or composition of mineral phases in a surface material [1]. Although this approach is potentially subject to systematic errors, it provides the only consistent set of asteroid surface material characterizations. Parametric determinations of asteroid mineralogy are relatively insensitive to " space weathering " processes on asteroids [2]. This is very important because while it is evident that optical alteration (under the general rubric of " space weathering ") is occurring on asteroid surfaces, data from spacecraft encounters with asteroids 443 Eros and 253 Ida have made it clear that the process differs from object to object [3]. Moreover the different relative variances of color, albedo and spectral slope between Eros, Ida and the Moon indicate that the asteroid alteration process is not simply an attenuated version of the well-understood lunar-style space weathering (the nanophase iron model-[4,5]). The spectral parameters used to quantitatively determine mineralogy from an asteroid spectrum are not differentially effected until the degree of space weathering (in any of its proposed forms) is far more extensive than expected (or observed) on asteroid surfaces. By contrast, curve matching depends on factors such as absorption band depth and spectral slope which are often significantly affected by even comparatively low degrees of space weathering [3,6-8]. Survey vs. Characterization Spectra: Much of the spectral data obtained for asteroids is not appropriate for compositional analysis. Such spectra lack the spectral coverage, spectral resolution and/or the signal-to-noise required to extract the suite of diagnostic spectral parameters. These survey-mode spectra are useful for providing a broad qualitative picture of asteroid relationships. A contribution of such surveys is to identify specific targets for more detailed quantitative investigation in order to better understand their detailed histories and relationships. To bring the picture into focus, as it were. Our ability to investigate asteroid compositional histories and genetic relationships is thus dependent upon obtain robust mineralogical characterizations of