Asteroid Bennu isotopes link it to Ryugu and rare CI meteorites
- Isotope measurements of pristine asteroid Bennu match rare CI carbonaceous chondrites and asteroid Ryugu, pointing to a formation zone just beyond the ancient water-ice line rather than the...
- NASA's OSIRIS-REx mission delivered roughly 120 grams of asteroid Bennu material to Earth in September 2023.
- Isotopes are alternate versions of the same element containing different numbers of neutrons.
Isotope measurements of pristine asteroid Bennu match rare CI carbonaceous chondrites and asteroid Ryugu, pointing to a formation zone just beyond the ancient water-ice line rather than the distant comet-forming region. Researchers at ETH Zurich analyzed titanium, chromium, and iron isotopes in samples returned by NASA’s OSIRIS-REx mission to determine where the primitive material originated in the early Solar System.
Isotopic Analysis Links Bennu to Ryugu and Rare Meteorites
NASA’s OSIRIS-REx mission delivered roughly 120 grams of asteroid Bennu material to Earth in September 2023. Researchers at ETH Zurich received a portion of these samples for detailed laboratory analysis. The team measured several isotopes of titanium, iron, and chromium across five Bennu sample portions that represented different particle types and sample masses.
Reading the Elemental Fingerprints of the Early Solar System
Isotopes are alternate versions of the same element containing different numbers of neutrons. Their relative abundances serve as distinct fingerprints because different regions of the early Solar System inherited unique mixtures of ancient stellar material. By comparing these signatures, scientists can trace relationships that are not visible through appearance alone.
The titanium and iron isotope compositions proved remarkably consistent among the analyzed Bennu samples. Chromium showed slightly more variability, which researchers linked to later alteration by liquid water inside Bennu’s parent body. Despite those minor differences, Bennu overlaps strongly with asteroid Ryugu and rare CI meteorites, indicating all three bodies incorporated a similar reservoir of early Solar System material.
A Chemical Hybrid That Defies Traditional Categorization
That close chemical relationship places Bennu in a distinct family that differs from most known meteorites and asteroids. While primitive meteorites traditionally fall into noncarbonaceous inner Solar System groups and carbonaceous outer Solar System groups, Bennu complicates that division. Its iron isotope compositions overlap more closely with inner Solar System material than many other carbonaceous meteorites do.
Bennu is a hybrid: the material does not clearly match either the inner or the outer Solar System,
Jupiter and the Water-Ice Line in the Protoplanetary Disk
The hybrid chemical signature led researchers to reevaluate older models that placed the parent bodies of Bennu-like asteroids far out in the remote comet-forming region. Instead, the study published in Science Advances points to a formation zone just outside the young Solar System’s water-ice line. This transition zone allowed fine dust from both inner and outer regions to meet and mix.
The new data suggest that early Jupiter played a central role by acting as a size-selective filter. The giant planet likely trapped larger particles while allowing smaller dust grains and fragments to drift across its orbit, eventually incorporating into the material that formed Bennu.