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CREDIT NASA and the European Space Agency
Research papers from NASA’s OSIRIS-REx mission shed new light on the early solar system using the analysis of asteroid Bennu samples - some of which have been studied at London’s Natural History Museum.
Snapshot of the solar system’s beginnings
One of the papers is the first major study of the chemistry of Bennu, published today in Nature Astronomy, revealing that the sample is chemically primitive and contains a mixture of materials with diverse origins: the inner solar system, the outer solar system, and beyond.
The international team of scientists have uncovered a rich diversity of ancient materials in samples from the near-Earth asteroid Bennu, revealing a snapshot of the early solar system more pristine than any meteorite on Earth. The findings shed new light on the complex origins of Bennu’s parent body, and the raw ingredients that gave rise to the planets.
The OSIRIS-REx mission, which delivered over 120 grams of Bennu’s regolith to Earth in 2023, has now allowed researchers to trace the origin of those grains back over 4.5 billion years. The samples contain rare components known as presolar grains - stardust that condensed around dying stars before our Sun formed. Researchers also found organic matter from the outer solar system and the interstellar medium, and high-temperature materials that likely formed close to the Sun before drifting outwards.
“We were surprised to find higher abundances of this organic matter and minerals from the inner solar system in the Bennu sample compared to asteroid Ryugu and CI chondrites,” said Dr. Ann Nguyen, co-lead author of the paper at NASA’s Johnson Space Center.
“We’re looking at unique snapshot of the outer solar system at the birth of our Sun,” said Prof. Sara Russell, planetary scientist at the Natural History Museum, and co-author on the paper. “Some of these grains have survived billions of years of solar system evolution almost untouched and can tell us more about the environment in which planets were born.”
"Our goal was to unmask where in the solar system and from which starting ingredients Bennu’s parent asteroid formed," said Jessica Barnes, professor at the University of Arizona and co-lead author of the paper. "We find that the returned samples contain components of diverse origins that survived geological processing within the parent asteroid. Our data suggest that Bennu’s parent asteroid formed in the outer parts of the solar system, possibly beyond the orbit of Saturn."
Unlike meteorites, these returned samples were in a protective capsule when they passed through Earth's atmosphere, making them ideal for understanding planetary formation and decoding early planetary processes. The analysis reveals that Bennu’s parent asteroid was formed from a remarkably diverse mixture of materials from across the solar system brought together in a cold, outer region of the protoplanetary disk.
Ancient water held in Bennu
Meanwhile, a paper published in Nature Geosciences reveals a record of water-driven chemical reactions that began over 4.5 billion years ago, before Earth itself had fully formed.
The newly analysed particles of Bennu, studied here at the Museum in South Kensington, are dominated by hydrated minerals known as sheet silicates. These fine-grained structures preserve a history of alteration by liquid water at low temperatures (~25°C), similar to the conditions recorded by other primitive space rocks like asteroid Ryugu and rare Ivuna-type (CI) chondrite meteorites.
“Bennu’s samples give us a direct window into an ancient world,” said Dr. Ashley King, a planetary scientist at the Museum who has studied the return sample and co-authored the paper. “They’ve been untouched by Earth’s atmosphere and so offer a clearer look at the chemical reactions that shaped early asteroids.”
The team of researchers noted how different Bennu is from most meteorites that fall to Earth. Unlike typical carbonaceous chondrites that contain millimetre-sized spherules called chondrules, Bennu is instead rich in ultra-fine dust that likely formed in the outer solar system.
“Studying Bennu has given us the opportunity to investigate a novel type of space rock, and we are learning new things about it every day” said the NHM’s Prof. Sara Russell, one of the leaders of the study. “The lack of reaction with the Earth’s atmosphere has given us the opportunity to study the history of the asteroid, and the evolution of the minerals it contains, in incomparable detail. Such asteroids likely impacted Earth ever since it was born and can help us understand how we came to live on a habitable planet.”
Other features such as layered carbonates and iron-rich sulphides paint a complex picture of chemistry in action. Some of the minerals likely formed, dissolved, and reformed over time due to interactions with water.
“These samples are a cosmic time capsule,” said Dr King. “They help answer one of the biggest questions in planetary science, how did water and organic material reach the early Earth?”
With further analysis underway, researchers hope to refine their understanding of Bennu’s parent body, its relationship to other primitive asteroids, and how materials from the outer reaches of the solar system shaped the early planets.
ENDS
Images available here.
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