NASA’s asteroid Bennu samples reveal a 4.5-billion-year-old secret
Tiny samples from asteroid Bennu are rewriting scientists' understanding of how our Solar System formed. New evidence suggests that Bennu was born where material from the inner and outer Solar System mixed, with Jupiter playing a surprising role in shaping its formation.
Key points
- Analysis of samples returned from asteroid Bennu suggests its material formed near the Solar System's water-ice line from a mix of inner and outer region dust.
- Researchers say Jupiter's early growth may have acted as a barrier that let fine dust mix while blocking larger particles.
- Bennu's chemistry closely resembles that of asteroid Ryugu and rare CI meteorites, hinting at a shared ancient source.
A chemical analysis of material returned from asteroid Bennu is offering new clues about how the Solar System formed about 4.5 billion years ago. The research, published in Science Advances, challenges earlier ideas about where Bennu originated and suggests Jupiter played a major role in shaping the material that built it and other ancient objects.
NASA's OSIRIS-REx mission collected the samples and delivered them to Earth in a capsule that landed in the Utah desert on September 23, 2023, carrying roughly 120 grams of asteroid material. Maria Schönbächler, Professor of Isotope Geochemistry at ETH Zurich, received half a gram in her laboratory for study.
A shared chemical fingerprint
The ETH Zurich team measured isotopes of iron, titanium and chromium to identify Bennu's chemical signature. Iron and titanium were found to be distributed very evenly through the material, and the analysis showed a close chemical relationship between Bennu, the asteroid Ryugu and rare primitive meteorites known as CI meteorites.
The researchers propose that the material behind Bennu, Ryugu and CI meteorites accumulated near the water-ice line, a boundary where water vapor could freeze. There, dust from the inner and outer Solar System mixed, with water ice helping small particles stick together into larger bodies.
Bennu is a hybrid: the material does not clearly match either the inner or the outer Solar System
— Maria Schönbächler
Jupiter's role in mixing
Jupiter formed within about one million years of the Sun's birth, and as it gained mass its gravity reshaped material in the surrounding disk. The researchers suggest the growing planet acted as a barrier that blocked most larger particles while allowing fine dust to move around it and mix near the water-ice line.
This scenario could explain Bennu's water-bearing material and its chemical resemblance to the Sun. Schönbächler said Bennu's material does not clearly match either the inner or outer Solar System, and that it may offer a glimpse of the original mix of elements from which the terrestrial planets were built. She added that the team now wonders whether other asteroids share the same isotopic signature.
