Asteroid Bennu offers fresh clues to solar system’s birth

Asteroid Bennu, the target of NASA’s OSIRIS-REx mission, contains fragments that predate the solar system along with material altered by water and space weathering, according to three newly published scientific papers.

The samples, delivered to Earth by the spacecraft in 2023, are providing researchers with the most detailed record yet of the asteroid’s history. Scientists report evidence of stardust from long-dead stars, organic compounds likely formed in interstellar space, and minerals that once interacted with liquid water.

The first study, published in Nature Astronomy, concludes that Bennu formed from the remains of a larger parent asteroid that broke apart after collisions in the asteroid belt. That body was made up of material from across the solar system and beyond, some of it dating back more than 4 billion years.

Researchers also found that minerals in Bennu’s parent asteroid reacted with water at low temperatures, according to a second study in Nature Geoscience. The water likely came from ice that melted as a result of heat from impacts or radioactive decay. Much of the material was transformed in this process, leaving minerals in which water is still locked.

A third paper in Nature Geoscience shows that Bennu’s surface has been reshaped by micrometeorite impacts and exposure to solar wind. These processes are known as space weathering and appear to be happening faster than expected.

Scientists say the findings underline the importance of sample return missions. Unlike meteorites that fall to Earth, Bennu’s pristine fragments have avoided contamination from the atmosphere, giving researchers a clearer picture of the building blocks that shaped the early solar system.