The first-ever samples collected from the far side of the Moon by China's Chang'e-6 mission have yielded a surprising and significant discovery: fragments of a rare, water-rich meteorite that offers new clues about how Earth may have acquired its water.
The Chang'e-6 Mission and Landing Site
In June 2024, the Chang'e-6 mission successfully returned to Earth with approximately 1,935.3 grams of lunar soil and rock, marking a historic first for a sample return mission from the Moon's far side—the hemisphere that perpetually faces away from Earth.
Landing Location: The probe landed in the Apollo Basin, which lies within the immense South Pole–Aitken (SPA) Basin. The SPA Basin is one of the largest and oldest impact craters in the solar system, making this region a prime target for finding ancient, preserved material.
Scientific Value: Scientists targeted this area to gather material potentially ejected from the Moon's deep interior by the colossal impact that formed the SPA basin. Furthermore, the Moon's lack of atmosphere and geological activity (like plate tectonics) means its surface acts as a pristine archive of the early Solar System's impact history, which has been largely erased on Earth.
Discovery of Water-Rich Meteorite Fragments
Upon analysis of the returned regolith (lunar soil), scientists from the Guangzhou Institute of Geochemistry (GIG) identified a handful of microscopic fragments that did not originate from the Moon itself.
Rare Fragments: These fragments were identified as relics of CI (carbonaceous-Ivuna) chondrites, a type of meteorite notable for being extremely rich in water (bound up in hydrated minerals) and organic compounds.
Outer Solar System Origin: CI chondrites are believed to have originated in the outer Solar System and are incredibly fragile and porous. On Earth, they are exceptionally rare, making up less than one percent of all collected meteorites, as they tend to break up or are chemically altered by our planet's atmosphere and water.
Preservation on the Moon: The Moon's bone-dry, airless environment provided the perfect conditions to preserve these fragile relics after their parent asteroid impacted the surface. Advanced analyses—including measuring key elemental ratios (e.g., iron, manganese, zinc) and, crucially, triple oxygen isotope ratios—confirmed their extraterrestrial, CI chondrite-like origin.
Implications for Earth's Water
The discovery of CI chondrite fragments on the far side of the Moon has major implications for a long-standing question in planetary science: Where did Earth get its water?
Volatile Delivery Hypothesis: The presence of these volatile-rich meteorites on the Moon's surface strongly supports the hypothesis that carbonaceous asteroids from the outer Solar System frequently migrated inward and bombarded the Earth-Moon system in the early history of the Solar System.
Water Carrier: CI chondrites are considered one of the most important candidates for the delivery of water and other essential volatile compounds (substances that are easily vaporized, like carbon dioxide and nitrogen) to the inner planets.
Challenging Assumptions: The apparent abundance of CI-like material in the Chang'e-6 samples (estimated to be as high as 30% of the non-lunar material) suggests that these water-carrying asteroids may have played a much larger role in seeding the early Earth and Moon with water than was previously estimated based solely on the rarity of CI chondrites on Earth.
The Chang'e-6 samples, by providing a preserved record from a uniquely ancient and undisturbed lunar region, offer direct physical evidence that will help scientists quantify the contribution of volatile-rich impactors to the water reservoirs of the inner Solar System.