NASA’s Bennu Samples Reveal Clues to the Solar System’s Formation
Chemical analysis of samples from asteroid Bennu suggests that the ancient body formed near the young Solar System’s water-ice line, where dust from its inner and outer regions mixed about 4.5 billion years ago. NASA’s OSIRIS-REx mission delivered approximately 120 grams of material to Earth on September 23, 2023; researchers at ETH Zurich examined half a gram, comparing isotopes of iron, titanium and chromium.
The results, published in Science Advances, show that Bennu shares a distinctive isotopic fingerprint with asteroid Ryugu and rare, carbon-rich CI meteorites. Their chemistry differs markedly from that of other known asteroids, meteorite groups and planets, challenging the long-standing view that primitive asteroids such as Bennu formed farther out, near the region associated with comets.
The researchers propose that Jupiter, which began forming within roughly one million years of the Sun’s birth, acted as a barrier to larger particles while allowing fine dust to circulate and mix near the water-ice boundary. Ice helped particles stick together, while repeated evaporation and condensation may have concentrated water in the material that became Bennu. This scenario could explain both the asteroid’s water-bearing minerals and its Sun-like elemental composition. Because Bennu has undergone relatively little chemical alteration, its samples may preserve an unusually representative record of the ingredients from which the rocky planets formed, while also offering clues to the early distribution of water and organic compounds relevant to life.
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