Chang'e-6 Samples Yield First Physical Evidence of CI Chondrite Impacts

Analysis of samples returned by China's Chang'e-6 mission in June 2024 has resulted in the identification of seven microscopic dust grains originating from Ivuna-type carbonaceous chondrites, known as CI chondrites. This finding, detailed in a study published in October 2025 in the Proceedings of the National Academy of Sciences, provides the first direct physical evidence that these volatile-rich meteorites bombarded the Moon billions of years ago.

Scientists at the Chinese Academy of Sciences (CAS), led by Jintuan Wang and Zhiming Chen, examined over 5,000 returned lunar fragments, focusing on pieces containing olivine. Using electron microscopy, spectroscopy, and mass spectrometry, the team confirmed the seven grains' chemical composition did not match native lunar or terrestrial material. Isotopic analyses, including iron-manganese ratios and oxygen and silicon isotopic signatures, classified the grains definitively as CI chondrites.

This classification is scientifically significant because CI chondrites are the most volatile- and water-rich of all meteorites, sometimes containing up to 20% water by mass in hydrated minerals. The preservation of these grains—formed from impact ejecta flash-heated above 1,600 Kelvin and rapidly quenched in the lunar vacuum—suggests the Moon is a superior archive for these primordial materials compared to Earth, where their extreme fragility causes them to pulverize during atmospheric entry.

The Chang'e-6 landing site, the Apollo Basin situated within the vast South Pole-Aitken (SPA) Basin on the Moon's far side, was selected for its potential to harbor ancient debris. The CAS team concludes that these impacts were fundamental in seeding the early Earth-Moon system with water and organic compounds, supporting the theory that CI chondrites were crucial vectors during bombardment epochs like the Late Heavy Bombardment, which occurred between 4.1 and 3.8 billion years ago.

Furthermore, the chemical signatures of the recovered grains closely resemble the composition of asteroids Ryugu and Bennu, which were studied by Japan's Hayabusa2 and NASA's OSIRIS-REx missions, respectively. Preliminary statistical analysis by the CAS team suggests that CI chondrites may constitute up to 30% of the Moon's total meteorite collection, a figure substantially higher than their terrestrial representation of less than one percent. The successful retrieval of these fragile relics, part of the 1,935.3 grams of regolith returned in 2024, validates the scientific value of far-side lunar samples for reconstructing the Solar System's initial chemical inventory.