The Moon's farside shallow subsurface structure unveiled by Chang'E-4 Lunar Penetrating Radar

On 3 January 2019, China's Chang'E-4 (CE-4) successfully landed on the eastern floor of Von Kármán crater within the South Pole-Aitken Basin, becoming the first spacecraft in history with a controlled landing on the farside of the Moon. Here, we report the results of the subsurface observations made by the Lunar Penetrating Radar onboard the Yutu-2 rover during the first two lunar days. We found a signal penetration at the CE-4 landing site that is much greater than that measured by the CE-3 LPR. The CE-4 radargram and tomographic images provide clear information about the structure of the landing site subsurface, which is primarily made of low-loss, highly porous, granular materials with embedded boulders of different sizes; the radar data also indicate that the top of the mare basal layer should be deeper than 40 m. These results represent the first high resolution image of a lunar ejecta sequence ever produced and the first direct measurement of its thickness and internal architecture.