China’s Yutu-2 rover has been spending intense time on the Moon for some time now. Transported to the far side of the Moon by the Chang’E-4 lander in January 2019, it traveled more on the lunar surface than any other rover, collecting various measurements. Now, for the first time, it has looked deeper than ever, 300 meters below the Moon’s surface, and has uncovered some interesting surprises.
The device called Lunar Penetrating Radar (LPR) has two channels that can reach different depths depending on the frequency used, and collects echoes by sending radio waves deep into the ground. Different materials produce different echoes. Low-frequency waves can penetrate deeper into the Moon, while higher-frequency waves reveal more details of the lunar surface soil, the materials just below the regolith.
The Yutu-2 crew used LPR to map the 40 meters near the surface in 2020, but the rover has now provided a more detailed look at the upper 300 meters of the Moon’s surface along its path. Five different layers of material were detected below a depth of 90 meters, and the thickness of each layer was highly variable, from 70 meters to 20 meters. In general, the deepest layers were also the thickest.
The team says this gives us information about past volcanism on the Moon. Our natural satellite was once a highly geologically active object with lava flowing from its surface. The Maria, the seas of the Moon, are considered large basalt plains created by volcanic activity, such as the Von Kármán crater in the South Pole-Aitken Basin, where Chang’E-4 landed.
The data seem consistent with a series of basalt eruptions that occurred billions of years ago. The team thinks that the decrease in thickness indicates that the rate of lava effusion decreases after each subsequent eruption. This is considered consistent with the general pattern of volcanism on the Moon. Volcanism seems to have become increasingly rare as our moon ages and cools.
Observations with high-frequency radar were mostly focused on the upper 40 meters. This part consisted mostly of rock debris and regolith, but several different layers emerged. In addition to all this, a buried crater was found among the rubble.
The study was published in JGR Planets.
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