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L.A. McFadden (U.Maryland), D.D. Wellnitz, C.O. Gross, M.L. Schnaubelt (U. Maryland), M.J. Gaffey (RPI), J.F. Bell III, B.E. Clark (Cornell U.), N. Izenberg, S. Murchie (JHU/APL), P. Martin (ESA), C.R. Chapman (SWRI), MSINIS Science Team
Near-Infrared reflectance spectra of 433 Eros were analyzed from low phase angle, high S/N data where the instrument foot print was 2.5 x 5 km. The two dominant spectral features at 1 and 2 microns are due to olivine and orthopyroxene (Fs59Wo11). The band parameters: band minimum and band area ratio (BAR) of the 2-micron/1-micron bands were calculated after a continuum was removed from calibrated and photometrically corrected spectra. These combined parameters are related to the chemical composition of olivine and orthopyroxene and their relative proportions.
Laboratory mixtures of olivine and orthopyroxene (Cloutis et al. 1986) were converted to NIS band passes. Band parameters were calculated for laboratory mixtures. Relative reflectance ratios of mixtures at 5% proportional intervals were calculated against a 80/20 mixture. Individual spectra ratioed to the average show a sinusoid shape if the band center shifts relative to the average. Band depth variations are seen in changing amplitude of the relative ratio. These form the template against which this NIS analysis is performed.
The observed Eros band parameters indicate a ratio of pyroxene/(olivine + pyroxene) ranging from 21-27% over the 83% of the northern hemisphere measured by NIS during the low phase flyby. One of the individual 2.5 x 5 km regions at the western end of Eros, shows a relative reflectance ratio indicative of a 5% compositional variation. The average band parameters are consistent with LL ordinary chondrite meteorites but the pyroxene chemistry is closer to primitive achondrites which are partial melt assemblages. At the scale of 2.5-5 km the northern hemisphere's surface composition is uniform to +/-3%. This research was supported by NASA through APL FCPO 779806.
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