The Chang'E-4 mission (CE-4) landed on the eastern floor of the Van Kármán crater, near the Moon's south pole, on Jan. 3, 2019. It deployed its Yutu-2 rover, which uses Lunar Penetrating Radar (LPR) to investigate the underground it roams and found that the subsurface at the CE-4 landing site is much more transparent to radio waves.

Due to that, radio signals reached a depth of 40 meters using a 500 MHz frequency - more than three times the depth previously reached by CE-3. This data allowed the researchers to develop an approximate image of the subsurface stratigraphy. 

The researchers combined the radar image with tomographic data and quantitative analysis of the subsurface. They concluded that the subsurface is essentially made by highly porous granular materials embedding boulders of different sizes. The content is likely the result of a turbulent early galaxy, when meteors and other space debris frequently struck the Moon. The impact site would eject material to other areas, creating a cratered surface atop a subsurface with varying layers.


Subsurface stratigraphy seen by Yutu-2 radar on the far side of the moon. Image: CLEP/CRAS/NAOC

The results of the radar data collected by the LPR during the first 2 days of lunar operation provide the first electromagnetic image of the far side subsurface structure and the first 'ground truth' of the stratigraphic architecture of an ejecta deposit.