Researchers have discovered an unexpectedly large number of presolar grains—dust from stellar explosions that predate our solar system—in samples of the near-Earth asteroid (101955) Bennu collected by NASA's OSIRIS-Rex spacecraft.
Characteristics of presolar grains of spinel-hibonite from the asteroid Bennu. Image credit: Nguyen etc.., two: 10.1038/s41550-025-02688-3.
“Presolar stardust grains are found in trace amounts in meteorites, interplanetary dust particles, Antarctic meteorites, samples of comet 81 P/Wild2 returned by NASA's Stardust mission, and samples of the carbonaceous asteroid Ryugu returned by JAXA's Hayabusa2 mission,” said Dr. Anne Nguyen of NASA Space Center. named after Johnson and her colleagues.
“Their highly anomalous isotopic composition is the result of nucleosynthetic reactions in evolved red giant stars, supernovae and novae.”
“The mineralogy and chemistry of presolar grains can be used to constrain condensation conditions and study the consequences of secondary alteration, as these grains are subject to alteration or destruction in space, in the solar nebula, and within planetesimals.”
In the study, the scientists analyzed presolar grains found in two different rock types in the Bennu samples.
The samples contained six times more grains than any other astromaterial studied, suggesting that the asteroid's parent body formed in a region of the protoplanetary disk enriched in dust from dying stars.
The study also shows that while Bennu's parent asteroid was extensively altered by fluids, there are still pockets of less altered material in the samples that provide clues to its origins.
“These fragments retain higher levels of organic matter and presolar silicate grains, which are known to be easily destroyed by water changes in asteroids,” Dr Nguyen said.
“Their persistence in the Bennu samples was unexpected and shows that some material escaped changes in the parent body.”
“Our study reveals the diversity of presolar material that the parent planet accreted as it formed.”
A paper The study results were published on December 2 in the journal Nature Astronomy.
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AN Nguyen etc.. Abundance of supernova dust and heterogeneous water changes detected by stardust in two lithologies of asteroid Bennu. Nat Astronpublished online December 2, 2025; doi: 10.1038/s41550-025-02688-3
