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The reflectance spectrum of Callisto from 0.2 to 4.1 ??m is modeled using a simultaneous intimate plus areal mixture solution of ice and dark material which satisfies absorption band depths and reflectance levels. The model uses the radiative transfer theory based on Hapke's (1981, J. Geophys. Res. 86, 3039-3054) work, optical constants of materials and includes effects of grain size and abundance of each material. The best-fitting models contain 20-45 wt% ice in the optical surface. The models indicate that the ice component of the surface is fairly large gained and that the ice cannot account for major spectral features beyond approximately 2.5 ??m. In this spectral region other hydrated minerals must dominate. A variety of reasonably well-fitting models were found and the amount of ice determined for these best fits was mathematically removed from the original Callisto spectrum. All of the spectra determined for the non-material were quite similar to each other and have absorption features that resemble hydrated silicates bearing both oxidation states of iron. Certain features in the Callisto non-ice spectrum can be duplicated by mixtures of Fe- and Mg-end member serpentines. Discrepancies indicate that other phases, possibly opaque minerals, are also required to match the entire spectrum. The unusual Fe-serpentines are commonly found in the matrices of primitive cabodnaceous chondrites, suggesting that other matrix phases may also be likely candidates for the Callisto non-ice material. ?? 1991.
Additional Publication Details
Modeling the reflectance spectrum of Callisto 0.25 to 4.1 ??m