The OSIRIS-REx Sample Analysis Team discovered that Bennu contains the primordial components that formed our solar system. The asteroid's dust is abundant in carbon and nitrogen, along with organic compounds, all vital for life. The sample also includes magnesium-sodium phosphate, an unexpected find, as it wasn't detected in the spacecraft's remote sensing data from Bennu. Its presence hints that the asteroid might have originated from a small, ancient, primitive ocean world.
A Phosphate Surprise
Analysis of the Bennu sample revealed fascinating insights into its composition. Predominantly composed of clay minerals, especially serpentine, the sample resembles rock types found at mid-ocean ridges on Earth, where mantle material encounters water.
This interaction not only forms clay but also produces minerals like carbonates, iron oxides, and iron sulfides. However, the most surprising discovery is the presence of water-soluble phosphates. These compounds are crucial in the biochemistry of all known life on Earth.
While a similar phosphate was identified in the asteroid Ryugu sample delivered by JAXA's Hayabusa2 mission in 2020, the magnesium-sodium phosphate in the Bennu sample is notable for its purity and the unprecedented size of its grains in any meteorite sample.
The discovery of magnesium-sodium phosphates in the Bennu sample raises questions about the geochemical processes that concentrated these elements and offers valuable clues about Bennu's historical conditions.
"The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid," said Dante Lauretta, co-lead author of the paper and principal investigator for OSIRIS-REx at the University of Arizona, Tucson. "Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation."
"OSIRIS-REx gave us exactly what we hoped: a large pristine asteroid sample rich in nitrogen and carbon from a formerly wet world," said Jason Dworkin, a co-author on the paper and the OSIRIS-REx project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
From a Young Solar System
Despite its possible history with water, Bennu remains a chemically primitive asteroid, with elemental proportions closely resembling those of the Sun.
"The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now," said Lauretta.
This composition offers a glimpse into the early days of our solar system, over 4.5 billion years ago. These rocks have retained their original state, having neither melted nor resolidified since their formation, affirming their ancient origins.
Hints at Life's Building Blocks
The team confirmed the asteroid is rich in carbon and nitrogen. These elements are crucial in understanding the environments where Bennu's materials originated and the chemical processes that transformed simple elements into complex molecules, potentially laying the groundwork for life on Earth.
"These findings underscore the importance of collecting and studying material from asteroids like Bennu - especially low-density material that would typically burn up upon entering Earth's atmosphere," said Lauretta. "This material holds the key to unraveling the intricate processes of solar system formation and the prebiotic chemistry that could have contributed to life emerging on Earth."
What's Next
Dozens more labs in the United States and worldwide will receive portions of the Bennu sample from NASA's Johnson Space Center in Houston in the coming months, and many more scientific papers describing analyses of the Bennu sample are expected in the next few years from the OSIRIS-REx Sample Analysis Team.
"The Bennu samples are tantalizingly beautiful extraterrestrial rocks," said Harold Connolly, co-lead author on the paper and OSIRIS-REx mission sample scientist at Rowan University in Glassboro, New Jersey. "Each week, analysis by the OSIRIS-REx Sample Analysis Team provides new and sometimes surprising findings that are helping place important constraints on the origin and evolution of Earth-like planets."
Launched on Sept. 8, 2016, the OSIRIS-REx spacecraft traveled to near-Earth asteroid Bennu and collected a sample of rocks and dust from the surface. OSIRIS-REx, the first U.S. mission to collect a sample from an asteroid, delivered the sample to Earth on Sept. 24, 2023.
Research Report:Asteroid (101955) Bennu in the laboratory: Properties of the sample collected by OSIRIS-REx
Related Links
OSIRIS-REx
Asteroid and Comet Mission News, Science and Technology
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