Earlier moon missions, including the Apollo series, performed some geophysical studies of the moon but the Chinese Chang’e lander has revealed the moon inner surface in much more detail.
The probe’s Lunar Penetrating Radar (LPR) scan of the moon’s far side detected porous and granular material and boulders beneath the surface. That’s a different kind of rock to that found on the moon’s near side and probably stemmed from material thrown up by a large impact such as by asteroids.
China’s lander touched down just over a year ago on the moon’s far side where no one had ever been before. That involved communications challenges, with the China National Space Administration (CNSA) initially launching a satellite to relay signals from the lander to Earth and back.
The Chang’e 4 lander and its Yutu-2 rover followed, successfully touching down on the moon’s far side in the Von Kármán crater, producing data ever since.
The latest comes from the LPR experiments, published in a new study and revealing composition down to a depth around 24 metres.
This study, published in the scientific journal Science Advances, represents an analysis of the first two lunar days – a lunar day lasts about an Earth month.
The paper said the results represent much deeper penetration into the lunar surface than previous missions, revealing a layer of homogenous material around 12 metres with sporadic rocks.
From 12 to 24 metres, there was a layer of mostly evenly distributed rocks up to a metre in diameter followed by a layer of boulders mixed with finer material.
The study said that taken together, the radar imagery indicated these were ejecta deposits, rocks that settled onto the surface following various asteroid impacts, mixed with fine grains over time.
“This work shows that 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,” the study said.
Professor Bradley Thomson from the University of Tennessee, who reviewed the paper, said these were convincing and exciting, given the challenge of conducting experiments on the moon’s far side.
“One can detect buried interfaces or rocks, but it is not always clear what those layers are, e.g. layers of impact crater ejecta, lava flow layers etc. Here it appears that layering is related to impact processes, not volcanic layers,” he said.
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