NEAR-IR REFLECTANCE SPECTROSCOPY OF NEAR-EARTH ASTEROID (23183) 2000 OY21: EVIDENCE FOR CA-RICH CLINOPYROXENE IN THE SURFACE ASSEMBLAGE
The presence of a second phase is suggested by a weak inflection at ~1.3-microns. While pure CPX are known to show a small inflection at that wavelength due to Fe2+ in M1 crystallographic site, the feature has also been observed in the spectrum of olivine, plagioclase feldspar and high-Fe orthopyroxene. Using calibration work described in Gaffey et al. (2002); we estimate the CPX chemistry to range from Wo51±3 Fs21±4 to Wo51±3 Fs7±4, given the uncertainties in Band II center. Spectra of Fe-poor (< Fs29) high-Ca CPX (diopside) show 2-µm absorption feature despite the high wollastonite content unless they have high Fe3+/Fe2+ ratio (Schade et al., 2004). The calculated chemistries plot in the high-Ca CPX region on the pyroxene quadrilateral, away from chondritic pyroxenes which have much lower Fe and Ca contents. We suggest that this assemblage formed from an extracted early partial melt of a chondritic parent body. An alternate interpretation of the spectrum would be a mixture of olivine with spinel which we think is unlikely based on the band parameters. This research was supported by NASA Near-Earth Objects Observations Program grant NNG04GI17G.