Abstract
Temperature probes onboard the Chang’E-4 (CE-4) spacecraft provide the first in situ regolith temperature measurements from the far side of the Moon. We present these temperature measurements with a customized thermal model and reveal the particle size of the lunar regolith at the CE-4 landing site to be ∼15 μm on average over depth, which indicates an immature regolith below the surface. In addition, the conductive component of thermal conductivity is measured as ∼1.53 × 10–3 W m–1 K–1 on the surface and ∼8.48 × 10–3 W m–1 K–1 at 1-m depth. The average bulk density is ∼471 kg m–3 on the surface and ∼824 kg m–3 in the upper 30 cm of lunar regolith. These thermophysical properties provide important additional ‘ground truth’ at the lunar farside, which is critical for the future analysis and interpretation of global temperature observations.