Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p12d0518k&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P12D-0518
Physics
6000 Planetology: Comets And Small Bodies, 6205 Asteroids And Meteoroids
Scientific paper
S-type asteroids, majority in asteroids, are believed to be parent bodies of ordinary chondrites, which are a large majority in meteorites. However, the steep reddened spectral slopes of S-type asteroids are different from those of ordinary chondrites. This spectral mismatch is considered to be caused by so-called 'space weathering' process, where high-velocity impacts of interplanetary dust particles should change the optical properties of the most upper regolith surface of asteroids. A recent simulation of space weathering showed that nanosecond pulse laser irradiation altered olivine and pyroxene spectra to be darker and redder, and their absorption bands became weaker relative to their untreated samples [1]. In the rims of olivine grains, nanophase metallic iron particles, which were theoretically predicted, were observed by a transmission electron microprobe [2]. Especially, the laser-irradiation on olivine causes larger reduction of albedo and more reddening of reflectance spectra than that on pyroxene, which corresponds to the observation of asteroids [3]. Although S-type asteroids and ordinary chondrites should contain much olivine and pyroxene, the space weathering simulation on mixtures of olivine and pyroxene has not performed yet, except the theoretical simulation. In order to simulate the heating by dust impacts, we irradiate nanosecond pulse laser beam onto the powdered olivine + orthopyroxene mixtures. The laser-irradiated samples show significant reduction of overall spectra (250-2500nm) and reddening. To investigate the difference of spectra by mixing ratio, we note the absorption band area and continuum slope. The spectral alteration of olivine-orthopyroxene mixtures upon laser irradiation is not proportional to the ratio. On 1μ m band area of olivine + enstatite samples, the effect of olivine is larger than that of enstatite . On 1μ m band continuum slope of olivine + hypersthene mixtures, the effect of hypersthene is shown larger than that of olivine . [1]Yamada et al., Earth Planets Space, 51, 1255-1265, 1999. [2]Sasaki et al., Nature, 410, 555-557, 2001. [3]Hiroi and Sasaki, Meteoritics and Planetary Sciences, submitted, 2001.
Kurahashi Erika
Sasaki Satoshi
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