A strikingly elevated concentration of presolar grains—cosmic dust originating from stellar explosions that occurred before our Solar System’s inception—has been identified within the specimens retrieved from the near-Earth asteroid (101955) Bennu by NASA’s OSIRIS-REx mission.
Characterization of a presolar spinel-hibonite grain from the asteroid Bennu. Image credit: Nguyen et al., doi: 10.1038/s41550-025-02688-3.
“These presolar stardust grains are typically found in minuscule quantities within meteorites, interplanetary dust particles, Antarctic meteorites, the samples procured from comet 81 P/Wild2 via NASA’s Stardust endeavor, and the samples from the carbonaceous asteroid Ryugu returned by JAXA’s Hayabusa-2 mission,” stated Dr. Ann Nguyen of NASA’s Johnson Space Center, along with her collaborators.
“Their profoundly atypical isotopic signatures stem from nucleosynthetic processes occurring within aging red giant stars, supernova events, and novae.”
“The mineralogical and chemical attributes of presolar grains can serve to establish the conditions under which they condensed and to investigate the impacts of subsequent alteration, given that these grains are prone to modification or disintegration in the vacuum of space, within the primordial Solar Nebula, and while embedded in planetesimals.”
In the course of this investigation, the scientific team meticulously examined presolar grains discovered in two distinct rock types present in the Bennu samples.
The analyzed samples contained an amount of these grains six times greater than that found in any other astromaterial previously subjected to study, indicating that the parent body of this asteroid coalesced in a region of the protoplanetary disk that was particularly rich in the particulate matter shed by deceased stars.
Furthermore, the research elucidates that despite the parent asteroid of Bennu having undergone significant alteration due to the action of fluids, certain reservoirs of less-modified materials persist within the samples, offering valuable insights into its formative history.
“These fragments still harbor a greater concentration of organic material and presolar silicate grains, which are known for their susceptibility to facile destruction through aqueous alteration within asteroids,” Dr. Nguyen remarked.
“Their enduring presence in the Bennu samples was an unexpected discovery and underscores that some constituents managed to evade alteration on the parent body.”
“Our findings reveal the considerable variety of presolar materials that the parent body incorporated during its formation process.”
A scientific publication detailing these discoveries was issued on December 2 in the esteemed journal Nature Astronomy.
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A.N. Nguyen et al. Abundant supernova dust and heterogeneous aqueous alteration revealed by stardust in two lithologies of asteroid Bennu. Nat Astron, published online December 2, 2025; doi: 10.1038/s41550-025-02688-3
