OPTICAL EFFECTS OF REGOLITH PROCESSES ON S-ASTEROIDS AS SIMULATED BY LASER SHOTS ON ORDINARY CHONDRITE AND OTHER MAFIC MATERIALS

Laboratory results from a simulation of possible optical effects of im pact melting and repeated crystallization on asteroidal surfaces are p resented. Quick melting and crystallization of surface materials were simulated by impulse laser treatment of powdered materials in vacuum. The mafic materials used in this study were: ordinary chondrite (OC) E lenovka L5, carbonaceous chondrite Allende CV3, terrestrial olivine, c linopyroxene, and olivine-clinopyroxene mixture 1:1. The reflectance s pectra of powdered samples before and after laser treatment were recor ded in the range 0.3-25 mu m. The laboratory laser alteration produced a reduction in overall reflectance and spectral contrast, a noticeabl e increase in spectral slope, the shifts in the wavelength positions o f absorption band centers, and a decrease in band area ratio. The cont inuum slope of the ordinary chondrite Elenovka after laser treatment i s comparable to that of S-type asteroids. Laser impulse alteration rai ses the spectrally derived olivine/orthopyroxene ratio of Elenovka fro m 2.8 to 5.4. This value is far outside the OC range, but falls within the olivine/orthopyroxene range for S-asteroids. The results suggest that quick melting and subsequent crystallization can enhance the spec tral similarity between S-asteroids and ordinary chondrites. (C) 1996 Academic Press, Inc.