Impact craters reveal granular behavior of regoliths

The surface of the Moon and Mars are covered in loose, powdery debris called regolith that is subjected to micrometeorite impacts and space weathering. With interest in space exploration growing, understanding how these regoliths respond to impacts is increasingly important to future drilling and building projects.

Ishii et al. investigated the low-velocity impacts at a granular level of the lunar highland, lunar mare and Martian regoliths, which are all known to have different physical and mechanical properties from soils on Earth. Using simulated regoliths developed by other groups, the researchers dropped a spherical ball into containers to create small craters.

They studied the sink depth created by each impact with 3-D scans. Because of the regolith’s high static electricity, the researchers used X-ray micro-computed tomography techniques to ensure they got high-resolution images. The results showed the sink depths to be much greater in the lunar and Martian regoliths than those created in a terrestrial silica sand column.

“The results indicate that the lunar and Martian regolith surfaces are less resistant against the impact of spherical projectiles,” said author Arata Kioka. “From the results, our scaling laws further highlight the significant differences in geomechanical properties between the terrestrial sand and the lunar and Martian regolith.”

While the regolith was well simulated, the researchers were not able to investigate the same properties in different gravity environments of the Moon and Mars.

“Our future studies will focus on overcoming these challenges and conducting similar laboratory experiments to better understand the granular behavior of regolith,” Kioka said.

Source: “Low-velocity impact response of lunar and Martian regolith simulants: Implications for lunar and Martian surface explorations,” by Takuma Ishii, Arata Kioka, Jyh-Jaan Steven Huang, Yoshiki Tabuchi, and Yasuhiro Yamada, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0233884 .