A study published September 23, 2026, found that iron and titanium isotope measurements from asteroid Bennu overlap with those from Ryugu and CI chondrites within analytical uncertainty. The authors combine those results with petrographic and chemical evidence to propose that Bennu’s parent body accreted just outside the young Solar System’s water-ice line and inside Jupiter’s orbit.
What the Bennu isotope study measured
The study reports nucleosynthetic isotope measurements of iron (Fe), titanium (Ti) and chromium (Cr) in five portions of Bennu material. Isotopes are forms of the same element with different numbers of neutrons; comparing their proportions can help trace relationships among planetary materials.
The Fe and Ti measurements were indistinguishable within analytical uncertainty across the analyzed portions, at sample amounts spanning roughly 20–1,300 milligrams. Results from analyses at ETH Zurich and Lawrence Livermore National Laboratory also overlapped within analytical uncertainty.
NASA records that the OSIRIS-REx mission delivered the Bennu sample to Earth on September 24, 2023.
How Bennu compares with Ryugu and CI chondrites
Bennu’s Fe and Ti isotope data overlap with measurements from Ryugu and CI chondrites, a group of carbon-rich meteorites. The overlap supports a shared material relationship; it does not mean Bennu, Ryugu and the meteorites came from the same body.
Chromium tells a more varied story. Its isotope measurements show small-scale differences among Bennu samples, which the study’s authors associate with aqueous alteration—changes caused by water interacting with material inside the parent body. The Fe and Ti results therefore should not be taken as a claim that every measured isotope is uniform at every scale.
A proposed setting just outside the water-ice line
The authors interpret the combined isotope, petrographic and chemical evidence as a link to a dust reservoir with affinities to both inner- and outer-Solar-System material. Their model places CI-like parent bodies just outside the water-ice line—the region in the early planetary disk beyond which water could freeze—and inside Jupiter’s orbit.
In that proposed scenario, Jupiter’s growth may have impeded larger particles, while fine dust mixed across disk regions and moved inward. The model places the accretion of these bodies about two million years after calcium-aluminum-rich inclusions formed. The water-ice-line setting is an inference from the evidence, not a directly observed location for Bennu’s parent body.
