^1,2Yun Chen et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2025JE009293]
¹National Key Laboratory of Aerospace Mechanism, Harbin Institute of Technology, Harbin, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
Published by arrangement with John Wiley & Sons

Micrometeoroid impacts play a key role in space weathering during the evolution of lunar regolith. The micro-cratering morphology and material transformation of common lunar phases are effective ways to understand the interaction between the space environment and matter, but there are few systematic studies. Micro-analysis is conducted on the microcraters in the Chang’e-5 lunar soil to evaluate the microscale impact effects. Here, our study reveals the different morphological characteristics and internal microstructure of microcraters across five typical components (pyroxene, olivine, plagioclase, ilmenite, and glass). The impact effects include planar defects like dislocation slip, amorphization, and the formation of np-Fe0 and vesicles. Key parameters, including the microcrater depth to diameter ratio and microcrater diameter to impactor diameter ratio, are calculated to quantify microcrater morphology. The formation process of microcraters is reproduced with the smoothed-particle hydrodynamic method. The results suggest that the microcraters retain transient characteristics, likely from low-speed micrometeoroids or secondary impact events. These microscale impacts exhibit lower intensity compared to microcraters from Apollo samples, indicating weak space weathering processes on young basalt. The exploratory work tries to provide a comprehensive summary of low-speed impact-induced microcraters in lunar soil and outlines the theoretical frameworks for understanding microscale impact processes.

¹Takaharu Saito, ¹Kengo Iwamoto, ²Shigekazu Yoneda, ³Seung-Gu Lee, ¹Hiroshi Hidaka
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.11.013]
¹Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8601, Japan
²Department of Science and Engineering, National Museum of Nature and Science, Tsukuba 305-0005, Japan
³Geology and Space Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea
Copyright Elsevier

Neutron-capture reactions are fundamental processes driving isotopic variations among cosmic-ray-irradiated planetary materials. The energy spectra of neutrons interacting with these planetary materials provide insights into their cosmic-ray exposure conditions and enable quantitative estimates of neutron-induced isotopic shifts in elements of interest. In this study, we measured Yb and Hf isotopic compositions of Apollo15 deep drill core samples, which provide information on higher-energy neutrons compared with conventional neutron indicators of Sm, Gd, and Er. Furthermore, we developed a calculation method to reconstruct a neutron spectrum from isotopic shifts in Sm, Gd, Er, Yb and Hf. Applying the method to Apollo 15 samples revealed significant neutron spectrum variations in the lunar subsurface. The observed epithermal neutron spectrum variations likely reflect depth dependence of energy moderation processes of neutrons. A neutron spectrum at the lunar surface estimated from our data is enriched in lower-energy epithermal neutrons compared with those calculated from numerical calculations in previous studies. The depth-dependent spectrum variations observed in the Apollo 15 samples possibly affect correction calculations of neutron-capture effects for nuclides strongly influenced by epithermal neutrons, such as ¹⁷⁶Hf. This is important in the context of accurate interpretation of radiometric and isotopic studies of lunar samples, which often record significantly high neutron fluences due to long-time cosmic-ray exposure on the lunar surface.