Temperature‐Dependent Changes in the Normal Albedo of the Lunar Surface at 1,064 nm

Abstract

AbstractOver the extreme temperature variations experienced in a single lunar day (∆T ≈ 300 K), particular minerals common to the lunar surface show spectral changes at discrete near‐infrared wavelengths in laboratory settings (Roush & Singer, 1986, 1987, https://10.1111/10.1029/JB091iB10p10301, https://10.1111/10.1016/0019-1035(87)90026-1; Singer & Roush, 1985, https://10.1111/10.1029/JB090iB14p12434). Variations in temperature can cause variations in the size and shape of crystallographic sites, which control the position, shape, and depth of crystal field absorptions. At an observation wavelength of 1,064 nm, the Lunar Orbiter Laser Altimeter (LOLA) should be highly sensitive to temperature‐dependent changes of orthopyroxene. Here we analyze temperature‐dependent spectral changes of the lunar surface as measured from orbit by LOLA. We couple LOLA measurements of normal albedo with measurements of surface temperature from the Diviner Lunar Radiometer Experiment, analyzing the maria and highlands between ±50°. We provide the first evidence of temperature‐dependent spectral changes on the lunar surface from orbital observations, finding that the majority of the surface between ±50° demonstrates a small, yet measurable, negative change in 1,064‐nm albedo with temperature (−∆R/∆T). The measurable effect is on the order of a few percent change in reflectance per ~80 K, indicating that temperature changes do not have a large effect on measurements of albedo at the sensitivity of the LOLA instrument. Stronger −∆R/∆T values tend to be associated with regions with elevated orthopyroxene, and the maria typically have higher levels of orthopyroxene and stronger −∆R/∆T values than the highlands. Our results suggest that single‐wavelength lasers may be powerful tools for understanding the distribution of particular minerals on the lunar surface.