CHANGE OF MINERAL REFLECTANCE SPECTRA BY MICORMETEORITE IMPACTS : SPACE WEATHERING AND EVOLUTION OF THE SURFACE OF SOLAR SYSTEM BODIES

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In the present study of space weathering, we aimed to clarify the relation between nanophase iron particles and spectral change using pulse laser irradiation simulating micrometeorite impact heating, We measured reflectance spectra of mid-infrared region (between 1.6 and 26 micron) which have not been measured using a FT/IR instrument introduced in this study. For an olivine sample after once 30mJ laser beam irradiation, 20-30% decrease in reflectance was observed. Especially high reflectance peak around 10 micron was attenuated. On the other hand, reflectance decreases after multiple laser irradiation were not significant, which was different from reflectance change of visible-NIR region.To discuss the relation of amounts of nanophase iron particles and reflectance change, we measured electron spin resonance of irradiated samples. For both olivine and pyroxene samples, amounts of nanophase iron particles increase at higher space weathering degree. In pyroxene samples, some saturation effect of nanophase iron particles was observed.