Analysis of material collected from asteroid Bennu by NASA’s OSIRIS-REx mission is providing new insights into the formation of the Solar System approximately 4.5 billion years ago. The spacecraft successfully retrieved roughly 120 grams of asteroid material, which landed in Utah in 2023. Scientists at institutions worldwide, including ETH Zurich, received portions of the samples for detailed investigation. Research published in Science Advances has identified distinctive chemical patterns that shed light on where Bennu originated and how ancient celestial materials combined during the Solar System’s earliest period.
Researchers examining isotopes of iron, titanium, and chromium in the Bennu samples discovered that the asteroid shares remarkably similar chemical signatures with asteroid Ryugu and a rare group of meteorites known as CI meteorites. This isotopic fingerprint indicates that these objects formed from materials originating in the same ancient cosmic reservoir. The chemical composition of these three bodies differs substantially from other known asteroids, meteorite groups, and planets, providing a distinctive identifier of their shared heritage. The close relationship among these objects suggests they developed under comparable conditions during the Solar System’s infancy.
The findings challenge previous scientific assumptions about where primitive asteroids formed. Rather than originating in the distant outer Solar System as traditionally believed, evidence indicates that Bennu, Ryugu, and CI meteorite parent bodies accumulated near the water-ice line, a boundary region in the disk surrounding the young Sun where temperatures were cold enough for water vapor to freeze. At this location, materials traveling from both inner and outer Solar System regions could mix extensively, with water ice facilitating the binding of fine particles into larger bodies.
Jupiter appears to have played a significant role in enabling this mixing process. The gas giant formed rapidly, within approximately one million years of the Sun’s birth, and its growing gravitational influence began restructuring material distribution throughout the disk. Researchers propose that Jupiter essentially functioned as a barrier, preventing larger particles from crossing its orbital region while allowing finer dust to circulate around it. This fine dust from different disk regions could then intermingle near the water-ice boundary, ultimately forming the parent bodies from which Bennu and related objects developed.
The proposed formation mechanism could explain key characteristics of Bennu, including its abundance of water-bearing material and its chemical resemblance to the Sun’s elemental composition. The extensive mixing of fine dust particles near the water-ice line would have created material that retained a representative sample of early Solar System ingredients, while Jupiter’s influence on larger particle movement helped concentrate water in the forming asteroid.
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