In a study published in Science Advances, researchers described how the Lunar Penetrating Radar (LPR) on Chang'E-4’s Yutu-2 rover sent 500 MHz radio waves deep into the surface of the Moon, reaching a depth of 40 meters. This is more than three times the depth reached by previous mission Chang'E-3, helping to paint a much richer picture of the structure and layers that form the Moon’s subsurface.
"We found that the signal penetration at the Chang'E-4 site is much greater than that measured by the previous spacecraft, Chang'E-3, at its near-side landing site," said study author LI Chunlai, a research professor and deputy director-general of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).
"The subsurface at the Chang'E-4 landing site is much more transparent to radio waves, and this qualitative observation suggests a totally different geological context for the two landing sites."
The researchers combined the radar image with tomographic data and quantitative analysis of the subsurface. They concluded that it is essentially made up of highly porous granular materials embedding boulders of different sizes. According to the Chinese scientists, this is probably 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 sitting above a subsurface with varying layers.
"The results illustrate, in an unprecedented way, the spatial distribution of the different products that contribute to from the ejecta sequence and their geometrical characteristics," LI continued.
"This work shows the extensive use of the LPR could greatly improve our understanding of the history of lunar impact and volcanism and could shed new light on the comprehension of the geological evolution of the Moon's far side."