When China's Chang'e-6 probe returned to Earth in June 2024, it carried a cargo of unprecedented scientific value: the first-ever samples collected from the far side of the Moon. Now, a research team led by Beihang University has unveiled the first high-throughput, non-destructive characterization of these precious materials, revealing that the "soil" on the lunar far side possesses unique physical properties which are vital for future lunar bases.
The study combines high-resolution X-ray micro-computed tomography (Micro-CT) with advanced deep learning algorithms to virtually reconstruct over 349,000 individual lunar soil particles. The findings suggest that the far-side regolith is significantly more irregular in shape than its near-side counterparts, leading to higher shear strength.
"Understanding the physical and mechanical properties of lunar regolith is the prerequisite for any engineering activity on the Moon," said Siqi Zhou, an associate professor at the School of Transportation Science and Engineering at Beihang University and a co-corresponding author of the study. "However, since these samples are too precious for traditional destructive testing, we developed a 'Digital Twin' approach to simulate their behavior without crushing a single grain."
The "Digital Twin" of Moon Soil
To analyze the samples without damaging them, the team employed a semi-supervised deep learning framework. This AI-driven approach processed terabytes of CT scan data to digitally extract 3D models of the particles, overcoming the challenges of separating thousands of tiny, tightly packed grains (Fig. 1).
The analysis revealed a striking difference: Chang'e-6 particles are much more "rugged" and irregular than samples from the Apollo missions or the Chang'e-5 near-side mission. "We found a lower sphericity—about 0.74—in the far-side samples compared to the near side," explained Feng Li, co-corresponding author of the study. "Unlike the smoother grains often found on Earth, these particles are angular and sharp. This morphology is likely a result of the unique impact history and space weathering environment of the South Pole-Aitken basin."
A Stronger Foundation for Future Bases
Does this irregularity matter? According to the study's Discrete Element Method (DEM) simulations, it matters significantly. The "spiky" shape of the particles creates a strong "geometric interlocking" effect—like how irregular gravel holds together better than smooth marbles.
The simulation results showed an internal friction angle of 47.96° and a cohesion of 1.08 kPa, values that exceed those typically estimated for near-side soil by the Surveyor and Apollo missions. "This means the ground on the lunar far side might be 'stiffer' and provide better bearing capacity than we previously thought," said Zhou. "This is positive news for the construction of the International Lunar Research Station (ILRS), as it suggests a more stable foundation. However, it also poses new challenges for drilling and rover mobility systems, which may encounter higher resistance from this interlocking soil."
The study establishes a critical benchmark for the geotechnical properties of the lunar far side, providing essential data for engineers designing the next generation of lunar rovers, landing pads, and habitats.
Sources: https://spj.science.org/doi/10.34133/research.1064
