For the first time since exploring the moon, scientists have been able to visualize what lies up to 300 meters below its dusty surface. The results, obtained by instruments on board China’s Yutu-2 rover, part of the Chang’e-4 mission, reveal more than a billion years of previously unknown lunar history.
Since landing on the far side of the moon in 2018 (which no one had done before), Yutu-2 has captured stunning panoramas of impact craters and collected mineral samples from the lunar mantle. And now, for the first time, the spacecraft has allowed scientists to visualize the layered structure that makes up the first 300 layers of the lunar surface. The results of this research have just been published in the Journal of Geophysical Research: Planets.
The Chinese rover is equipped with a technology called Lunar Penetrating Radar (LPR). According to Jianqing Feng, a researcher at the Institute of Planetary Sciences in Tucson, Arizona, and the paper’s first signatory, the device allows the robotic vehicle to send radio signals to the lunar surface. “Then,” Feng explains, “listen to the echoes as they come back.” Therefore, scientists can use these “echoes” (radio waves bouncing off underground structures) to create a map of the lunar surface. In 2020, scientists were already using Yutu-2’s LPR to map the first 40 meters below the surface but had not previously penetrated deeper. 40 meters, which, according to new data, consists of several layers of dust, dirt, and broken rock.
But there was so much more. Hidden among these materials, Feng said, was a crater that formed when a large object crashed into the moon. The researchers assume that the debris surrounding this formation was ejecta, i.e., debris from the impact. As scientists delved deeper, they discovered up to five different layers of lunar lava accumulated over billions of years.
According to the most widely held theory, the moon formed 4.510 million years ago, just after the solar system itself, when an object the size of Mars collided with Earth, detaching a large fragment of our planet. Later, the moon continued to be bombarded by objects from space for about 200 million years. Some of these impacts ripped open the lunar surface. Like Earth, the lunar mantle then contained pockets of magma, molten material that Feng says seeped through newly formed fissures in a series of violent volcanic eruptions.
New data from the Chang’e-4 mission shows that this process slowed down over time. Feng and his colleagues found that the layers of volcanic rock thinned the closer they got to the lunar surface. This suggests that modern eruptions flow less lava than older ones. “The moon, explains the researcher, – slowly cooled and lost steam in its last volcanic stage. His energy waned over time.”
Volcanic activity on the moon is thought to have stopped completely about a billion years ago (although scientists have uncovered much more recent evidence of isolated volcanic activity, as young as 100 million years old). Because of this, the moon is often considered “geologically dead.” However, according to Feng, there could still be magma at depth, many meters below the surface. Something that the rover Yutu-2, which has not yet finished its work, could reveal in the near future.
