Sample return: ground truth for meteoritics

Samples collected directly from known bodies test the links that meteoriticists have proposed for decades, and reveal what meteorites alone cannot.

Lunar samples

The six Apollo landings returned about 382 kilograms of lunar rock and soil between 1969 and 1972, and three Soviet Luna missions returned about 300 grams. These samples, with known locations, made it possible to recognise lunar meteorites in 1982.

China's Chang'e 5 returned about 1.7 kilograms in 2020 from a young volcanic region, and its basalts were dated to about 2.0 billion years, extending the record of lunar volcanism and recalibrating the crater-counting chronology used across the Solar System. In 2024, Chang'e 6 returned about 1.9 kilograms from the South Pole–Aitken basin on the far side, the first samples from that hemisphere.

Lunar meteorites complement these by sampling many unvisited regions, though without geological context. Together, the two sources have refined models of the lunar magma ocean and crustal evolution.

Itokawa and space weathering

JAXA's Hayabusa mission returned around 1,500 particles from the S-type near-Earth asteroid Itokawa in 2010, despite technical problems that reduced the sample to tiny grains.

Analyses showed mineral and oxygen isotope compositions matching LL chondrites, mostly equilibrated, confirming the long-suspected link between S-type asteroids and ordinary chondrites. The grains showed thin rims with nanophase iron produced by space weathering, explaining the spectral differences between asteroids and meteorites.

Cosmic-ray and solar wind data from the grains indicated that surface material on Itokawa is lost relatively quickly, over timescales of millions of years. This means small asteroids continuously shed material, consistent with a rubble-pile structure, which was also evident in images of Itokawa's boulders and smooth regions. The mission thus answered a question that had puzzled researchers for decades.

Ryugu and Bennu

Hayabusa2 returned about 5.4 grams from the carbonaceous asteroid Ryugu in December 2020. NASA's OSIRIS-REx returned about 121.6 grams from Bennu in September 2023.

Ryugu samples resemble CI chondrites in mineralogy, chemistry and isotopes, but are more pristine: they lack sulphates and ferrihydrite that formed in museum CI meteorites through reaction with terrestrial air and water. They have therefore become an improved reference for Solar System elemental abundances.

Bennu samples, studied from 2023 onwards, are rich in hydrated minerals, carbonates and magnetite, and contain unusual sodium-rich phosphates and evaporite minerals, including halite and sodium carbonates, implying brines on the parent body. Reports in 2025 described 14 of the 20 amino acids used in terrestrial proteins and all five nucleobases used in DNA and RNA.

Both bodies are CC rubble piles, probably fragments of larger water-rich parent bodies.

Comet dust and lessons learned

NASA's Stardust mission collected dust from comet 81P/Wild 2 in aerogel and returned it in 2006. Surprisingly, the comet contained high-temperature minerals, including a CAI-like particle and chondrule-like fragments, which formed close to the young Sun. This showed that material from the inner disc was transported to the region where comets formed.

Sample return missions have taught meteoriticists several lessons. Terrestrial alteration of meteorites, even of falls, is more significant than once thought for fragile carbonaceous chondrites. Space weathering is real and measurable. Small asteroids are often rubble piles. And meteorite collections are biased towards strong materials, as weak, porous asteroids may break up in the atmosphere.

Meteorites remain indispensable because they sample far more parent bodies than missions can visit, but returned samples now anchor their interpretation.

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