Thermophysical properties of lunar regolith revealed by thermal-infrared observations of Lunar Reconnaissance Orbiter (LRO) Diviner radiometer

The thermophysical properties of lunar regolith are crucial for the scientific and engineering issues in future lunar missions. In this work, we evaluate the thermophysical properties of lunar regolith between 75 • N and 75 • S from the bolometric temperature dataset of Diviner radiometer by treating the radius of lunar regolith grains as a proxy. By the ground-truth median/average grain radius and Diviner data at Apollo, Luna and Chang'E landing sites, we re-calibrate the reference rolling force for a grain radius of 47.5 m as 0.8 ± 0.1 × 10 −7 N. On the global scale, the estimated grain radius values are fairly uniform, focus mostly between 40 and 60 m and show an average value of ∼ 52.7 m. Some regions of Oceanus Procellarum, Mare Imbrium and Mare Frigoris show abnormally large grain radius 80-100 m, which are associated with the late high-Ti volcanism during 2.3-1.2 Ga within Procellarum KREEP Terrane (PKT). Mare Humorum is dated to be as old as 3.9 Ga, but still shows large grain radius values of ∼ 100 m that are far greater than those in other contemporaneous mares. Such an anomaly may indicate a distinguished evolution for the local lunar regolith. For the surficial lunar regolith on the global scale, the contact component of thermal conductivity varies mostly within 0.0008-0.0010 W/(m•K), whereas the radiative component normalized to 250 K varies mostly within 0.002-0.004 W/(m•K). The thickness of topmost loosely packed layer is estimated as 0.02-0.04 m. Besides, the thickening of loosely packed layer is more likely to be a natural consequence of the change of packing style associated with the decrease of grain radius during the space weathering.