Thermal Infrared Emission Spectroscopy of Salt Minerals Predicted for Mars

Thermal emissivity spectra (2000-400 cm^-1) of select carbonate, sulfate, phosphate, and chloride minerals are presented in this study. The suite of samples was chosen to most closely represent the chemistry of the salts predicted for Mars on the basis of the Viking lander data, theoretical and experimental studies, and analyses of the Shergottite-Nakhlite-Chassignite and ALH84001 meteorites. Midinfrared spectra are presented to demonstrate the variation in emissivity between evaporite mineral classes (e.g., carbonates versus sulfates) and within a mineral class (e.g., calcite versus dolomite). Additional emissivity spectra are presented of particle-size fractions for each of the four mineral classes to show the effects of increased energy scattering with decreased particle size. Understanding particle-size effects may be critical for interpreting the emission of Mars where particulate material is common. The unique appearance of the emissivity spectra will aid the identification of the salt minerals on Mars from the midinfrared vibrational data to be acquired by the Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft.