Analysis of Bennu samples points to the asteroid’s mixed origin — ScienceDaily
An isotopic analysis of samples from asteroid Bennu, delivered to Earth by NASA’s OSIRIS-REx mission, indicates that its material may have formed from mixed material from the inner and outer parts of the early Solar System. ScienceDaily reports on the study, published in the journal Science Advances.
The OSIRIS-REx capsule carrying approximately 120 grams of Bennu material landed in the Utah desert on September 23, 2023. The laboratory of ETH Zurich Professor of Isotope Geochemistry Maria Schönbächler received half a gram of material for analysis. Scientists studied isotopes of iron, titanium and chromium — the ratios of different forms of elements that can indicate the origin of material.
Similarity to Ryugu and CI meteorites
The researchers found that Bennu’s isotopic composition is similar to that of asteroid Ryugu and the rare group of primitive CI meteorites. This indicates that the source material of these objects may have originated from a common reservoir of ancient cosmic dust. At the same time, their chemical characteristics differ substantially from those of other known asteroids, meteorite groups and planets.
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It was previously believed that such primitive asteroids could have formed in the outer part of the Solar System, in regions where comets formed. The new analysis calls this assumption into question: the authors propose that material for Bennu, Ryugu and CI meteorites accumulated near the boundary where temperatures in the disk around the young Sun allowed water vapor to freeze.
The possible role of Jupiter
Under the proposed scenario, dust from the inner and outer regions of the disk mixed near this boundary, while water ice helped small particles stick together. Schönbächler called Bennu a “hybrid” because its material does not correspond unambiguously to either the inner or outer part of the Solar System.
The authors also suggest that Jupiter, which began forming during the first approximately million years after the Sun emerged, may have affected the movement of material in the protoplanetary disk. Its gravity may have restrained the movement of larger particles while allowing fine dust to bypass its orbit and mix. Further studies of samples from other asteroids are expected to determine whether such an isotopic signature is characteristic not only of Bennu and Ryugu.
