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 impact melting and repeated crystallization on asteroidal surfaces are presented. 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) Elenovka L5, carbonaceous chondrite Allende CV3, terrestrial olivine, clinopyroxene, and olivine-clinopyroxene mixture 1:1. The reflectance spectra of powdered samples before and after laser treatment were recorded in the range 0.3-25 [[micro]meter]. The laboratory laser alteration produced a reduction in overall reflectance and spectral contrast, a noticeable increase in spectral slope, the shifts in the wavelength positions of absorption band centers, and a decrease in band area ratio. The continuum slope of the ordinary chondrite Elenovka after laser treatment is comparable to that of S-type asteroids. Laser impulse alteration raises the spectrally derived olivine/orthopyroxene ratio of Elenovka from 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 spectral similarity between S-asteroids and ordinary chondrites.