Ice and minerals on Callisto - A reassessment of the reflectance spectra

The results of a comparison of laboratory spectral reflectance measurements of particulate mixtures of both hydrated silicates and palagonite with water ice, on the one hand, with two previously unpublished reflectance spectra of Callisto, yield direct support for the hypothesis that the measured reflectance of Callisto includes a substantial nonice component. Hapke's (1981) equations are used in a theoretical model for thorough analysis of telescopic data; a comparison of the calculation results thus obtained with measured reflectance data for Callisto indicate that three-component, ice/magnetite/serpentine mixtures are a better match for telescopic data than two-component ice mixtures.