What are the samples from Ryugu and Bennu?
They are pristine samples of two carbon-rich asteroids brought to Earth by spacecraft: about 5.4 grams from Ryugu by Japan's Hayabusa2 in 2020, and about 121.6 grams from Bennu by NASA's OSIRIS-REx in 2023.
Meteorites are wonderful, but they have been heated during their fall and exposed to air, water and life once on the ground. Carbon-rich meteorites are especially affected. To study truly untouched material, space agencies sent spacecraft to collect it directly from two small near-Earth asteroids, both dark, carbon-rich rubble piles less than a kilometre across.
Japan's Hayabusa2, launched in 2014, reached Ryugu in 2018. It collected samples twice in 2019, the second time near an artificial crater it made by firing a copper projectile into the surface. Its capsule landed in the Australian outback in December 2020 carrying about 5.4 grams of grains. NASA's OSIRIS-REx, launched in 2016, reached Bennu in 2018, grabbed surface material in October 2020, and dropped its capsule in the Utah desert on 24 September 2023. The sample, about 121.6 grams, is the largest ever returned from an asteroid. The spacecraft continues as OSIRIS-APEX, heading to the asteroid Apophis.
The findings have been remarkable. Ryugu's material closely resembles the rare CI chondrites such as Orgueil, the most chemically primitive meteorites, which are close to the Sun's own composition for non-volatile elements. Both asteroids contain clay minerals and carbonates formed when water flowed through their parent bodies. Ryugu samples contain amino acids and the nucleobase uracil. Bennu samples, analysed in studies published in 2025, contain 14 of the 20 amino acids used in proteins on Earth, all five nucleobases found in DNA and RNA, and salts left behind as salty water evaporated.
These are not signs of life, but they show that the chemical ingredients for life were widespread in the early Solar System and could have been delivered to the young Earth. Much of the material is being stored untouched for future scientists with better instruments.