Effects of Albedo on the MIR Emissivity Spectra of Silicates for Lunar Comparison.

We used laboratory analysis to investigate the effect of mineral albedo, as defined at 750 nm, on the midinfrared emissivity spectra of silicates under lunar environment conditions. Optical darkening has long been recognized as an effect of space weathering on the visible‐to‐near‐infrared spectra of the Moon. However, space weathering has not been as thoroughly investigated in the mid‐infrared. Because mid‐infrared spectra are strongly influenced by the anisothermality of the lunar surface environment, it is likely that any darkening effects of space weathering would also change the thermal gradient in heavily space weathered lunar regolith. To isolate this variable, we added nanophase carbon to particulate samples of forsterite, augite, and anorthite to achieve a range of albedo samples and measured their midinfrared spectra under lunar environment conditions within the Planetary and Asteroid Regolith Spectroscopy Environment Chamber at Stony Brook University. We observe a shift in the Christiansen Feature maximum to longer wavelengths and decreasing spectral contrast with decreasing albedo. These shifts are well correlated with the observation of space weathering effects on the Diviner Lunar Radiometer Experiment compositional data, and point to the need for further investigation into the effects of space weathering on the midinfrared spectra of airless bodies. Plain Language Summary: Space weathering is a major process on the Moon that matures lunar soils over time. In this work, we try to isolate one of the effects of space weathering, darkening, to determine its effects on our interpretation of midinfrared emissivity spectra. We do so by adding nano‐scale carbon particles to three silicate minerals and examine how the spectral features change as the sample gets darker under both ambient and simulated lunar environment conditions. We observe a decrease in overall spectral contrast and a shift in the Christiansen Feature (CF) position to longer wavelengths with increasing carbon content. This correlation between the darkening sample and CF value is similarly observed in the remote sensing data from Diviner Lunar Radiometer Experiment and Kaguya Multiband Imager instruments, demonstrating that it is an important factor to consider to accurately interpret composition from mid‐infrared data of space weathered soils on airless bodies. Key Points: Space weathering affects midinfrared data from the Moon largely by altering regolith albedoAlbedo affects the position of the Christiansen feature (CF) of minerals in the midinfrared under ambient and simulated lunar environment conditionsCorrelation between albedo and CF is shown in remote sensing data and laboratory experiments [ABSTRACT FROM AUTHOR]