Low-temperatureand low atmospheric pressure infrared reflectance spectroscopy of Mars soil analog materials

Abstract

Infrared reflectance spectra of carefully selected Mars soil analog material have been measured under low atmospheric pressures and tempertures. Chemically altered montmorillonites containing ferrihydrite and hydrated ferric sulfate complexes are examinated, aswel as synthetic ferrihydrite and a palagonitic soil from Haleakala, Maui. Reflectance spectra of these analog materials exhibit subtle visible to near-infrared features, which are indicative of nanophase ferric oxides or oxyhydroxides and are similar to features observed in the spectra of the bright regions of Mars. Infrared reflectance spectra of these analgs include hydration features due to structural OH, bound H2O and adsorbed H2O. The spectral character of these hydration features is highly dependent on the sample environment and on the nature of the H2O/OH in the analogs. The behavior of the hydration featuresnear 1.9 muem, 2.2 muem, 2.7 muem, 3 muem, and 6 muem are reported in spectra measured under a Marslike atmospheric environment. In spectra of these analogs measured under dry Earth atmospheric conditions the 1.9-muem band depth is 8-17%; this band ismuch stronger under moist conditions. Under Marslike atmospheric conditions the 1.9-muem feature is broad and barely disverible (1-3% band depth) in spectra of the ferrihydrite and palagonitic soil samples. In comparale spectra of the ferric-sulfate-bearing montmorillonite the 1.9 muem feature is also broad, but stronger (6% band depth). In the low atmospheric pressureand temperature spectra of the ferrihydrite-bearing montmorillonite this feature is sharper than the other analogs and relatively stronger (6% band depth). Although the intensity of the 3-muemband is weaker in spectra of each of the analogs when measured under MArslike conditions, the 3- muem band remains a dominant feature and is especially broad in spectra of the ferrihydrite and palagonitic soil.