Spectral comparison between olivine-rich asteroids and pallasites

概要

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Reflectance spectra of two pallasites were measured and compared with four reflectance spectra of olivine-rich asteroids. Bidirectional reflectance spectra (0.3-2.6μm) were measured at several different points on chips of Yamato-8451 (Y-8451) and Imilac pallasite. A metal-rich part of Y-8451 showed a reflectance spectrum very similar to 113 Amalthea. Other olivine-rich asteroids could not be fit well even by combining all the measured reflectance spectra of those two pallasites. Some kind of regolith process seems to be important in producing those reflectance spectra. Y-8451 is unusual as a pallasite. Its olivine grains are much smaller than usual pallasites, the Fa value is the lowest, and both orthopyroxene and inverted protoenstatite are present. Their Fe/(Fe+Mg) ratios correspond to the formation temperature of 1135℃. Y-8451 is rather similar to metal-rich primitive achondrites such as Y-791058,which is, therefore, also examined in this study. 113 Amalthea is another example of the S asteroids whose reflectance spectra can be approximated with a stony-iron model.
国立極地研究所の論文