Layered Structures in the Upper Several Hundred Meters of the Moon Along the Chang'E-4 Rover's First 1,000-m Traverse

Abstract

We revealed the layered structure of the upper three hundred meters of the lunar surface in the South Pole-Aitken Basin by using the measurements from the Lunar Penetrating Radar (LPR) onboard the Chang'E-4 rover. The result shows that five large strata are identified by the LPR 60-MHz channel below the depth of 90 m, with thicknesses ranging from 20 m to larger than 70 m. We speculate that at least three strata are basalt flows, while the shallowest stratum is composed of multiple thin lava flows. The thickness of the strata decreases with the decreasing depth, suggesting a progressively smaller lava effusion rate over time. To evaluate the reliability of the result, a comparison was made between Chang'E-4, Chang'E-3, and ground test low-frequency data. The LPR 500-MHz channel unveiled the structure of weathered material in the top ∼40 m, revealing several layers as well as a buried paleo crater and its ejecta blanket in the regolith.