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L.A. McFadden, N. Goldman (U. Maryland)
The first analysis of near-IR spectra of 433 Eros using the relationship between band area ratio and band position resulted in the conclusion that there are two pyroxenes and olivine present on the surface of Eros. An association with a sub-type of ordinary chondrite could not be made. In order to constrain the elemental composition of these minerals, we used recalibrated spectra of Eros (Izenberg et al. 2003) and Modified Gaussian Method (MGM) fitting (Sunshine et al. 1990) to determine a combination of absorption bands representing two pyroxenes and an olivine. A controlled fitting method, where the starting band positions were set to those expected of ordinary chondrites of H, L and LL types. We were able to define a set of absorption bands with residuals <0.008, that are consistent with band parameters of both a low-Ca, low-Fe orthopyroxene, and a higher calcium clinopyroxene such as are found in L-type ordinary chondrites. The band parameters are also consistent with those of olivine (Fo65). We investigated the differences in band center vs. composition relationship using band centers derived from both the minimum value and determined from MGM fitting. The scatter in band parameters is similar using both analysis approaches. We conclude that the crystallographic site consists of intrinsic scatter that results in a large uncertainty in deriving mineral composition from band parameters related to pyroxenes and olivines. The mineral composition of the surface of Eros is closest to that found among the L-type ordinary chondrites. MGM analysis provides an interpretation that is more specific than that possible using the band I vs. band area ratio of orthopyroxene and olivine mixtures. This work was funded by NASA grant NNG04GA92G.
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The author(s) of this abstract have provided an email address for comments about the abstract: mcfadden@astro.umd.edu
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.