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up ȁ80% of observed meteorite falls, but so far very few asteroid spectral analogs have been identified for these meLaboratory results from a simulation of possible optical effects of impact melting and repeated crystallization on asteroi-teorites. dal surfaces are presented. Quick melting and crystallizationThe S-asteroids are widespread in the inner belt and of surface materials were simulated by impulse laser treatment appear to consist mostly of olivine, orthopyroxene, and of powdered materials in vacuum. The mafic materials used metal. They resemble OCs spectrally but are characterized in this study were: ordinary chondrite (OC) Elenovka L5, car-by steep red continua unlike those of the OCs, and their bonaceous chondrite Allende CV3, terrestrial olivine, clinopy-spectrally derived mineralogies are far outside the OC roxene, and olivine-clinopyroxene mixture 1 : 1. The reflectance range (Gaffey et al. 1993a). Moreover, the character of the spectra of powdered samples before and after laser treatment rotational spectral variations of surfaces of two large were recorded in the range 0.3-25 m. The laboratory laser S-asteroids, 8 Flora and 15 Eunomia, appear to be inconsisalteration produced a reduction in overall reflectance and spectent with the primitive undifferentiated OC composition tral contrast, a noticeable increase in spectral slope, the shifts (Gaffey 1984, Gaffey andOstro 1987). Consequently, the in the wavelength positions of absorption band centers, and a majority of investigators are inclined to interpret S-type decrease in band area ratio. The continuum slope of the ordinary chondrite Elenovka after laser treatment is comparable asteroids as composed of various differentiated assemto that of S-type asteroids. Laser impulse alteration raises the blages which are the products of melting in the deep interispectrally derived olivine/orthopyroxene ratio of Elenovka ors of asteroid parent bodies. These materials are similar from 2.8 to 5.4. This value is far outside the OC range, but to stony-iron meteorites and some achondrites (Gaffey falls within the olivine/orthopyroxene range for S-asteroids. 1993a, Hiroi et al. 1993a).The results suggest that quick melting and subsequent crystalliThus, the source of ordinary chondrites remains unclear. zation can enhance the spectral similarity between S-asteroids On the basis of some spectral resemblance between the and ordinary chondrites.

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