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T.L. Roush (NASA Ames Research Center)
The Tagish Lake meteorite (TLM) has been suggested as a spectral analog for D-type asteroids based upon comparisons of spectral color and slope (Hiroi et al. 2001). To the extent that this correspondence of color (and albedo) is valid, then TLM can be considered a sample of one of the types of materials encountered in the outer solar system that may impart a characteristic red coloration to many of these surfaces. Theoretical modeling of the measured reflectance from planets and satellites has been used to infer compositional information, grain size, and relative abundance of the surface components. Such models inherently rely upon the optical constants, the real and imaginary indices of refraction, of candidate materials. If the optical constants of TLM were known, then these could be used for assessing whether or not this material can explain the range of color properties observed for outer solar system surfaces. The visible, near-infrared, and mid-infrared (0.3-25 microns) indices of refraction of TLM were derived from the reflectance measurements of Hiroi et al. (2001) using iterations between a Hapke-type model to determine the imaginary index and a subtractive Kramers-Kronig analysis to determine the real index of refraction. The imaginary index of TLM was compared to imaginary indices of refraction of the individual minerals representing those that have been identified in TLM (Zolensky et al. 2002). From this comparison it is clear that the imaginary indices of several individual minerals contribute to the estimated imaginary index of TLM.
This research is supported by NASA's Planetary Geology and Geophysics Program.
Hiroi, T., M. E. Zolensky, and C. M. Pieters (2001) Science, 293, 2234-2236.
Zolensky, M. E., K. Nakamura, M. Gounelle, T. Mikouchi, T. Kasama, O. Tachikawa, and E. Tonui (2002) Meteor. Planet. Sci., 37, 737-761.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.