Regolith Properties in the Chang'E-5 Landing Region of the Moon: Results From Multi-Source Remote Sensing Observations

In December 2020, China's Chang'E-5 (CE-5) spacecraft successfully collected 1.731 kg samples from Oceanus Procellarum on the Moon's nearside, becoming the first lunar sample return mission since Luna 24 in 1976. These samples, collected from one of the youngest mare basalt units within the Procellarum KREEP Terrain, are critical to deciphering several fundamental questions of the Moon. In order to provide geologic context for interpreting the returned samples, we conducted a comprehensive analysis of regolith properties in the landing region using optical, topographic, multispectral, thermal, and radar observations. The CE-5 landing site is within a flat, young mare basalt unit with intermediate titanium. A ballistic sedimentation model suggests that similar to 98% of the surface regolith are local materials. The dielectric permittivity of the regolith is estimated to be 2.96 + i0.03 based on its composition and porosity. Morphologies of small fresh craters identified in high-resolution optical images show that regolith thickness varies from similar to 1.5 to similar to 8 m with a median value of similar to 5 m, implying a large mean regolith growth rate over the landing region. A comparison between radar image and Lunar Reconnaissance Orbiter Diviner surface rock abundance (RA) map indicates that subsurface rocks play a significant role in producing the observed radar backscatter. Further analysis of the radar echo suggests that subsurface RA is similar to 0.47%-0.88% if the effective size is 3 cm, which can explain the shallow sampling depth of the CE-5 drilling device. All these results provide valuable information for understanding the geological context and properties of the returned regolith samples.