Rock abundance and evolution of the shallow stratum on Chang'e-4 landing site unveiled by lunar penetrating radar data

• Published in: Earth and planetary science letters 2021-06, Vol.564, p.116912, Article 116912
• Main Authors: Zhang, Ling, Xu, Yi, Bugiolacchi, Roberto, Hu, Bin, Liu, Cai, Lai, Jialong, Zeng, Zhaofa, Huo, Zhijun
• Format: Article
• Language: English
• Subjects: Chang'e-4 mission; ejecta; lunar penetrating radar; regolith; shallow stratigraphic structure; Von Kármán crater
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2021.116912

•CE-4 LPR data of the first 450 m drive reveal a ∼40 m deep subsurface structure.•Four ejecta layers underlying the surface regolith are discontinuous.•The energy map of suggests the cause of inconsistencies to be a buried crater.•The rock distribution indicates a brief weathering period of each ejecta layer.•The local evolutionary history is constructed based on the revealed stratigraphy. The Yutu-2 rover, part of the Chang'e-4 (CE-4) mission to the lunar farside, has been exploring the Von Kármán crater (VK) within the South Pole-Aitken (SPA) gathering data on its geology. The Lunar Penetrating Radar's (LPR) 500 MHz antenna reveals the subsurface structure up to 40 m in depth, which helps to construct models on the evolution of the shallow stratum. This work presents the analysis and interpretation of the data collected during the first twenty lunar days, from January 2019 to July 2020. Below an 11±4-meter surface regolith layer, the radar image reveals well-defined reflectors that are interpreted as discrete depositional layers. These marked density boundaries could indicate a geologically brief time interval between each arrival, which prevented the materials to undergo a deeper homogenization through space weathering. To investigate further, we generated a subsurface rock distribution map using the correlation of dual-channel antennas data from the same channel. Clusters of rocks located at the bottom of each ejecta stratum are revealed, probably sorted by size due to the statistically less frequent occurrence of larger impact events admixing the deeper-seated materials. The bowl-shaped outline discovered in both rock and LPR energy distribution maps is interpreted to represent a 150±30 m wide and 10±5 m deep paleo-crater that was excavated within three thin ejecta layers. The CE-4 LPR reveals a complex geological history within the Von Kármán crater with no fewer than four impact events delivering meters thick ejecta at the CE-4 landing area following the end of the infilling phase.