Thermal infrared emissivity measurements under a simulated lunar environment: Application to the Diviner Lunar Radiometer Experiment

Abstract

Here we present new laboratory spectral measurements of the major silicate minerals identified on the Moon (plagioclase solid series endmembers: albite and anorthite; clinopyroxene and orthopyroxene; and the olivine endmember forsterite) under lunar environmental conditions. We make the first characterization of thermal infrared spectral changes between ambient and lunar environment conditions over the 7 – 25 μm wavelength range for a fine-grained mineral suite and evaluate their application to lunar remote sensing data sets. The lunar environment introduces observable effects in thermal infrared emissivity spectra of fine grain minerals, which include: (1) a shift in the Christensen Feature (CF) position to shorter wavelengths, (2) an increase in the overall spectral contrast, and (3) decreases in the spectral contrast of the Reststrahlen Bands (RB) and Transparency Features (TF). Thus, our new measurements demonstrate the high sensitivity of minerals to environmental conditions under which they are measured and provide important constraints for interpreting new thermal infrared datasets of the Moon, including the Diviner Lunar Radiometer Experiment onboard NASA’s Lunar Reconnaissance Orbiter. Full resolution laboratory mineral spectra deconvolved to Diviner’s three spectral channels demonstrate that the spectral shape, CF position and band ratios can be used to distinguish between individual mineral groups and lunar lithologies. The integration of the thermal infrared CF position with near infrared spectral parameters allow us to make more robust mineralogical identifications and provide a framework for future integrations of data sets across two different wavelength regimes.