Asteroid Bennu holds stardust older than the Sun, hinting at clues to our Solar System's birth

Asteroid Bennu Samples Reveal Ancient Dust Older Than the Sun (Image: NASA)

The story of our solar system is written in dust, and scientists say a small asteroid has preserved it for billions of years. Tiny grains collected from asteroid Bennu are now offering rare clues about the birth of stars and planets, long before the sun itself existed.

What did scientists find in Bennu’s samples?
NASA’s OSIRIS-REx spacecraft collected Bennu’s samples in 2020 during a swift touch-and-go. The material contains ancient stardust, interstellar organic matter, and minerals formed from melted ice inside Bennu’s parent body. Researchers say around 80% of the asteroid is made up of minerals created when dust reacted with water. These grains hold chemical signatures of dead stars and represent important records of cosmic history.

A scanning electron microscope shows a micrometeorite crater on a Bennu particle. Three new studies reveal the asteroid’s samples hold diverse materials, including some older than the sun. (Image: NASA/Zia Rahman)

How old is the dust inside Bennu?
The findings, published in Nature Astronomy and Nature Geoscience, confirm some grains are older than the sun. Scientists call them presolar grains, many smaller than a micrometre and traceable only through unusual chemical fingerprints. Pierre Haenecour of the University of Arizona, who analysed the samples, described Bennu as a “time capsule” holding remnants from the solar system’s earliest days. Some grains even survived the catastrophic collision that destroyed Bennu’s parent asteroid millions of years ago.

What does Bennu's surface tell us about asteroids?
The asteroid’s airless surface has been shaped by space weathering, including constant solar wind and micrometeorite strikes. According to Lindsay Keller from NASA’s Johnson Space Centre, Bennu’s top layer has been exposed to cosmic rays for up to seven million years. Tiny craters and melted rock splashes reveal how quickly these processes change asteroid surfaces. Comparison with samples from Japan’s Hayabusa2 mission to Ryugu suggests impacts may play a larger role than scientists once thought.

Why does this discovery matter?
Meteorites that fall to Earth can provide limited information, but they rarely preserve a full history. OSIRIS-REx, however, mapped Bennu for over a year before sampling, offering context impossible to gain otherwise. Jessica Barnes of the University of Arizona, who led one of the studies, said the results highlight why direct space samples are essential. The dust inside Bennu is more than debris; it is evidence of stars, collisions, and the long memory of the cosmos.