Spectral hydration features in nominally anhydrous minerals & implications for lunar remote sensing

Abstract

The contributions of external and internal hydration (OH and H2O) on the shape and strength of hydration related features at 3 and 6 μm for lunar relevant nominally anhydrous minerals were investigated under vacuum conditions. Understanding the effect of hydration on the reflectance spectra of lunar analog materials in the laboratory can provide insights into remote sensing observations of the lunar surface and the potential for 3 and/or 6 μm observations to determine the speciation of hydration on the Moon. We demonstrate changes in the shape and strength of the broad 3 μm absorption feature in olivine and anorthite that is associated with the removal of hydration under changing environmental conditions. The overlapping nature of OH and H2O related absorption features in the ∼3 μm region makes it difficult to uniquely determine the speciation of hydration. Despite evidence of H2O loss in the 3 μm region, we do not observe the fundamental bending mode of H2O at 6 μm, posing potential challenges for the detection H2O on the lunar surface and throughout our solar system.