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Dust brought back to Earth by China's Chang'e-6 mission contains rare meteorite relics that could change our understanding of sources of water and other life-essential ingredients in our solar system.

In June 2024, Chang'e-6 returned the first-ever samples from the far side of the moon, the hemisphere that faces away from our planet. Recent analysis of these lunar materials in the journal Proceedings of the National Academy of Sciences reveals that water-rich asteroids, previously considered rare, may have contributed far more material to early Earth and the moon than previously thought.

Although we have learned much about the history of the solar system from space rocks that have landed on Earth, there is a problem. The atmosphere acts like a shield and burns up the most fragile, water-rich meteorites, so our understanding is incomplete. The moon, however, has a very thin atmosphere, and so it is better at preserving past impacts.

Researchers sifted through two grams of moon dust to hunt for fragments of carbonaceous chondrites (CI chondrites) because they are known to be packed with ingredients essential for life, including water and organic compounds. These types of meteorites are extremely fragile and rarely survive Earth's atmosphere or impact. They're also thought to be rare on the moon, but scientists found seven microscopic relics in the Chang'e-6 samples.

They confirmed this by first measuring ratios of metals like iron, manganese and zinc in the fragments, which told them they were unlike any other rocks on the moon. Analysis of the texture and structure showed that the fragments formed when a large rock melted when it smacked into the lunar surface. Finally, the researchers used a sophisticated instrument called a SIMS (Secondary Ion Mass Spectrometer) to measure the triple oxygen isotope signature of the fragments. Their chemical fingerprint matched that of CI-like carbonaceous chondrites.

"The identification of CI-like materials in this study enables us to reassess chondrite proportions in the Earth–moon system, given Earth's chondrite collection biases," write the researchers in their paper.

The team's work proves that Earth's meteorite collection is heavily biased and does not reflect the true mix of space rocks that hit the inner solar system (Earth and the moon). Because the moon preserved these fragments, it suggests that more volatile-rich and water-containing asteroids hit our planet and our nearest neighbor than previously estimated. "Our findings establish CI-like chondrites as a key reservoir of exogenous material delivered to the lunar surface," the authors conclude.

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