Chang’E-4 rover spectra revealing micro-scale surface thermophysical properties of the Moon

Abstract

Lunar surface temperature variations provide key information about the thermophysical properties of the regolith. To date, temperatures have been measured using telescopes and orbiter instruments, providing information from mid-to long infrared (IR) wavelengths. Here we report on temperature measurements in the short wavelength IR at centimeter scales observed in situ by the Chang’E-4 rover. These local observations are an important complement to the existing large-scale data. We show that even at 2.4 µm, where reflected radiation dominates the spectrum, thermal information can be retrieved from the data. The observed thermal radiances and derived temperatures depend on the observation geometry, specifically the relative azimuth angle between Sun and detector. This indicates that surface roughness on sub-resolution (millimeter) scales causes a non-Lambertian radiation pattern of the emitted flux that is per definition independent of the observation angle. This behavior must be considered when deriving temperatures and thermal properties of lunar regolith.