Regolith Properties in the Chang'E‐5 Landing Region of the Moon: Results From Multi‐Source Remote Sensing Observations. Issue 7 (12th July 2021) - Jia, Bojun
Abstract: 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 ∼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 ∼1.5 to ∼8 m with a median value of ∼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 ∼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. Plain Language Summary: In December 2020, China's Chang'E‐5 (CE‐5) mission successfully returned 1.731 kg samples from the Moon. These new samples will be helpful to answer many fundamental questions about the Moon. We performed a comprehensive analysis of the regolith characteristics over the region where the samples were collected. Our results show that the landing site is within a flat, young mare basalt unit, and that most surface regolith are local materials and their composition is relatively homogeneous. The regolith thickness varies from 1.5 to over 8 m, indicating that the regolith growth rate is much higher. Analysis of radar data shows that there are subsurface rocks at the landing site, which can be explained by the fact that the landing site is atop of the continuous ejecta of a degraded crater. These rocks could be potential obstacles for subsurface sampling, and can help to explain the limited drilling depth of the CE‐5 core tube. Our results provide valuable information for understanding the returned samples by CE‐5 mission. Key Points: The Chang'E‐5 spacecraft landed on a flat, young mare plain with ∼98% of surface regolith consisting of local mare materials Over the landing region of 6 km across, the median regolith thickness is ∼5 m and the mean dielectric permittivity is 2.96 + i0.03 Radar observations suggest that fraction of subsurface rocks within the 5 m regolith depth is ∼0.47%–0.88% if effective size is assumed as 3 cm