Linear mixture modeling of Europa's non-ice material based on cryogenic laboratory spectroscopy

Linear mixture modeling has been applied to Galileo Near Infrared Mapping Spectrometer (NIMS) spectra of Europa's dark, non-water-ice terrain using cryogenic laboratory spectra of hydrated compounds. Water ice alone could not account for the distorted and asymmetric spectral features attributed to water of hydration in the Europa spectrum. The modeling was conducted using cryogenic reference spectra of hexahydrite, epsomite, bloedite, sodium sulfide nonahydrate, mirabilite, magnesium sulfate dodecahydrate, sulfuric acid hydrate, and saturated brines of magnesium sulfate, sodium carbonate, and sodium sulfate. All were measured between 77 and 130K. The best model fit was attained using abundances of 14% hexahydrite, 11% bloedite, 12% mirabilite, and 62% sulfuric acid hydrate. Results indicate that sulfuric acid hydrate and hydrated sulfate salts, taken together, produce a better spectral match than either class of compound considered alone.