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.

Automated summary

In this study, laboratory analysis was used to investigate the effect of mineral albedo on the midinfrared emissivity spectra of silicates under lunar environment conditions. The study found that darkening effects of space weathering would change the thermal gradient in heavily space weathered lunar regolith, as shown by the shifts in the Christiansen Feature maximum to longer wavelengths and decreasing spectral contrast with decreasing albedo. These findings suggest the need for further investigation into the effects of space weathering on the midinfrared spectra of airless bodies.