Chang’e-6 Moon Soil Reveals 500-Million-Year Cosmic-Ray Exposure History

Fragments of rock carried back from the Moon's far side by China's Chang'e-6 mission have yielded new clues about how the giant South Pole-Aitken basin shuffled material across the lunar surface. By measuring cosmogenic isotopes of samarium, hafnium, and chromium in the returned soil and individual rock clasts, researchers determined that the Chang'e-6 soil has an average cosmic-ray exposure age of roughly 500 million years, indicating when its constituent material was excavated at the sampling site. Most of the low-titanium basaltic clasts in the sample set showed prolonged exposure histories similar to the host soil, suggesting they were dug up in the same excavation event.

However, two basaltic clasts stood out: they were excavated more recently, meaning their material traveled to the sampling site through a different or later impact process. The team then turned to the KREEP-bearing clasts. These clasts fell into two distinct compositional groups, and their cosmic-ray exposure ages did not overlap, pointing to separate excavation histories rather than a single provenance event.

In other words, the KREEP materials at the Chang'e-6 site arrived through more than one route. By comparing the clast compositions with remote-sensing observations of the lunar surface, the researchers identified candidate source regions: the magnesium-rich pyroxene annulus surrounding the basin for one compositional group, and buried basalt plains known as cryptomare for the other. Ejecta transport within and beyond the South Pole-Aitken basin therefore appears to have delivered geochemically distinct material to the far-side sampling location from multiple destinations.

The broader significance lies in the distribution of KREEP material. The study, published in Nature Communications as an open-access article, is based on Chang'e-6 samples from the South Pole-Aitken basin, though the authors note that effects of impact and space weathering on the lunar farside remain only partially constrained.

Subject of Research: Cosmic-ray exposure ages and ejecta provenance of Chang'e-6 samples from the South Pole-Aitken basin

Article Title: Cosmogenic isotopic evidence from Chang’e-6 clasts for excavation history and ejecta provenance in the South Pole-Aitken basin

Article References: Zhou, M., Zhang, Y., Chen, J., Luo, R., Wang, Z., Zuo, Z., Chen, D., Chen, K., Liu, K., Shen, J., Liu, B., & Qin, L. (2026). Cosmogenic isotopic evidence from Chang’e-6 clasts for excavation history and ejecta provenance in the South Pole-Aitken basin. Nature Communications. https://doi.org/10.1038/s41467-026-78270-w

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78270-w

Keywords: Chang'e-6, Moon, South Pole-Aitken basin, cosmic-ray exposure, cosmogenic isotopes, KREEP, lunar far side, ejecta, cryptomare, impact excavation, space weathering, Nature Communications