Recent findings from the Chang”e-6 mission, conducted by the China National Space Administration, have unveiled an astonishing discovery on the Moon”s far side. Researchers have identified traces of an unusual type of meteorite dust, specifically from a water-bearing class known as CI chondrites, which are rarely found intact on Earth due to their fragile nature.
CI chondrites are recognized as the most volatile and water-rich meteorites, containing significant amounts of hydrated minerals. Their composition is akin to that of other well-known space rocks, such as those from the asteroids Ryugu and Bennu. Due to their soft and porous structure, these meteorites typically disintegrate upon entering Earth”s atmosphere, making their survival rate exceedingly low. Consequently, CI chondrites constitute less than one percent of meteorites discovered on our planet.
The research team, led by geochemists Jintuan Wang and Zhiming Chen from the Chinese Academy of Sciences, meticulously examined over 5,000 fragments collected from a crater within the Apollo Basin, located in the expansive South Pole-Aitken Basin. This site was chosen for its potential abundance of ancient impact material.
Focusing on olivine, a mineral often found in volcanic rocks and meteorites, the scientists isolated several olivine-bearing fragments. Through advanced techniques such as scanning electron microscopy and secondary ion mass spectrometry, they identified seven fragments that chemically matched olivine from CI chondrites. These fragments exhibited porphyritic structures, indicating they originated from rapidly cooled impact melts.
The most surprising finding emerged from the chemical and isotopic analyses of these clasts. The iron-to-manganese ratios, along with measurements of nickel oxide and chromium oxide, revealed values inconsistent with both lunar and terrestrial origins. Instead, they aligned with characteristics expected from material within a CI chondrite asteroid that had impacted the Moon, melted, and preserved its chemistry for billions of years.
This discovery marks the first solid evidence that CI chondrites impacted the Moon during the early formation of the Solar System, providing insight into the Moon”s geological history. Intriguingly, the lunar environment may be more conducive to preserving such materials compared to Earth, with estimates suggesting that CI chondrites could represent up to thirty percent of the Moon”s meteorite collection.
For years, scientists have speculated that CI chondrites played a crucial role in delivering volatiles and water to the early Earth and Moon. The identification of these seven tiny grains of dust from the Moon”s far side lends credence to this hypothesis. Future lunar sample missions are anticipated to deepen our understanding of this phenomenon.
In their conclusion, the researchers noted, “Given the rarity of CI chondrites in Earth”s meteorite collection, our integrated methodology for identifying exogenous materials in lunar and potentially other returned samples offers a valuable tool for reassessing chondrite proportions in the inner Solar System.” The findings have been published in the Proceedings of the National Academy of Sciences.
