“The moon was slowly cooling down and running out of steam in its later volcanic stage. Its energy became weak over time.” These are the words of Jianqing Feng of the Planetary Science Institute and were quoted to Live Science. The words now ring with fresh insight as China’s Chang’e-4 mission lifts the veil on the far side of the moon and presents a geological history much richer than had previously been imagined.
In 2019, Chang’e-4 became the first spacecraft to accomplish the feat of a soft landing on the lunar far side, an area that is always out of Earth’s sight. Its Yutu-2 rover, armed with a sophisticated Lunar Penetrating Radar (LPR), ventured onto the pummeled floor of Von Kármán crater in the South Pole–Aitken (SPA) Basin, the largest impact structure on the moon. The main objective of the mission was to look below the surface, and the findings have been nothing but revolutionary.
The LPR system on Yutu-2 has two channels a 60 MHz antenna that can look as deep as over 300 meters, and a 500 MHz channel to look at the top 35 meters. By sending electromagnetic pulses into the ground and listening for their echoes, the LPR constructs a radargram a cross-sectional map of the underground. This technology, with its record-breaking 1–2 meter vertical resolution in the upper levels, has enabled scientists to differentiate between regolith, ejecta, and solidified lava flows with unprecedented accuracy, as outlined in Nature Communications.
The top 40 meters of the far side of the Moon, mapped by Chang’e-4, show a multifaceted stratigraphy of dust, soil, broken rock, and impact ejecta. But it’s what is below that really gets planetary scientists’ hearts racing. The LPR data revealed five different layers of ancient lunar lava, each representing an independent volcanic event. Those molten flows extended across the basin billions of years ago, slowly diminishing with each of the following eruptions. Thinning of these layers near the surface is evidence of the moon’s declining volcanic energy a cooling Earth burning off its internal heat.
The finding of a buried crater in these overlying layers is an added bonus. The formation, presumably produced by a giant impact, is encircled by a ring of ejecta debris scattered outward from the collision. The crater and ejecta are not just marks but are temporal indicators, useful for piecing together the timeline of cataclysmic events that sculpted the far side surface. As discussed in Interesting Engineering, the discovery of these features offers a glimpse into the early history of the moon’s violent past.
These results are not merely a list of ancient catastrophes. They contradict the prevailing assumption that the moon is “geologically dead.” Although most of the volcanic action is considered to have stopped between one billion and 100 million years ago, the existence of several, well-preserved layers of lava and the indication of deep magma reservoirs suggest the possibility that the interior of the moon can still harbor areas of heat and molten rock. “There could still be magma deep underneath the lunar surface,” Feng said to Live Science, with a world not so sleeping.
The history of these lava flows is inextricably bound up in the moon’s early history. The current consensus, bolstered by Chang’e-4 data as well as new isotopic research, is that the moon was created from debris left over when Earth collided with a Mars-sized object some 4.51 billion years ago. In the aftermath, the moon was shrouded in a worldwide magma ocean. When this ocean cooled and solidified, it separated into layers a process dated to have proceeded nearly to completion by 4.43 billion years ago, as indicated in a 2025 Proceedings of the National Academy of Sciences study. The remaining KREEP melt rich in potassium, rare earths, and phosphorus is an inorganic record of this early differentiation that persists in a chemical fingerprint, and whose distribution remains to be explored, particularly in the SPA Basin that Chang’e-4 targets.
Chang’e-4’s ground-penetrating radar data not only verify the existence of multiple, separate basalt units but also give a glimpse into their thickness, composition, and the order of volcanic and impact events. These radargrams are confirmed by in situ spectral and mineralogical data, which show differences in olivine and pyroxene abundance hints for the depth and origin of the magmas. The SPA Basin’s peculiar geology, characterized by an asymmetric nearside-to-farside distribution of volcanic deposits, could be associated with differences in crustal thickness and consequences of the SPA-forming impact itself.
The implications go beyond lunar science. LPR’s ability to discern such delicate details in the subsurface structure marks a new benchmark for planetary exploration. The same radar systems are being evaluated for use on missions to Mars, asteroids, and even icy moons, where subsurface layers could contain the keys to planetary evolution and habitability.
Chang’e-4’s continuing traverse of the far side continues to redefine our knowledge of the moon’s history. Every meter stepped, every radar pulse fired into the regolith, reveals new secrets about a world that, rather than being a frozen relic, is an active archive of solar system history. As Feng noted, “We are standing on the threshold of an era of groundbreaking lunar mapping,” a sentiment shared by the global community as they wait for new discoveries to be made from the shadowed side of Earth’s oldest friend.
