Shallow Regolith Structure and Obstructions Detected by Lunar Regolith Penetrating Radar at Chang'E-5 Drilling Site.

This work analyzes the observations from the Lunar Regolith Penetrating Radar (LRPR) onboard Chang'E-5 to reconstruct the subsurface structure of the regolith under the lander at the drilling site. This is the first stationary Ground-Penetrating Radar (GPR) array to operate on the Moon. Imaging results of pre-drilling and post-drilling measurements show that the thickness of local regolith is larger than 2 m. Within the LRPR's detection range, we do not find any continuous layer. Instead, irregular, high-density zones are identified in the regolith. Two of these zones are on the drilling trajectory at ~30 cm and ~70 cm, consistent with the recorded drilling process. We speculate a rock fragment from the deeper, high-density zone obstructed the drill, which led to an early termination of the drilling. Based on our interpretation of subsurface structure, we modeled the LRPR echoes using a finite-difference time-domain method. The same imaging algorithm was also applied to the simulation data. The modeled data verify our inference of the regolith structure under the lander. [ABSTRACT FROM AUTHOR]