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A surprise in the sample from the asteroid: its structure contains the "original ingredients" of the solar system

The OSIRIS-Rex sample analysis team found that the asteroid dust was rich in carbon, nitrogen, organic compounds and magnesium sodium phosphate, suggesting special historical conditions

Microscope image of a dark brown particle, about a millimeter long, with a light phosphate membrane. On the right is a smaller fragment that broke off. Credit: From Lauretta & Connolly et al. (2024) Meteoritics & Planetary Science, doi:10.1111/maps.14227
Microscope image of a dark brown particle, about a millimeter long, with a light phosphate membrane. On the right is a smaller fragment that broke off. Credit: From Lauretta & Connolly et al. (2024) Meteoritics & Planetary Science, doi:10.1111/maps.14227

The OSIRIS-Rex sample analysis team found that Nunu contains the original components that formed the Solar System. The asteroid's dust is rich in carbon and nitrogen, as well as organic compounds, all of which are essential components of life as we know it. The sample also contains magnesium sodium phosphate, which surprised the research team because it was not seen in the remote sensing data the spacecraft collected in Benno. Its presence in the sample suggests that the asteroid may have split off from a small primitive ocean world that has long since disappeared.

The sample return chamber, collected from his son in October 2020, shortly after landing in Utah. Credit: NASA/Keegan Barber
The sample return chamber, collected from his son in October 2020, shortly after landing in Utah. Credit: NASA/Keegan Barber

Launched on September 8, 2016, OSIRIS-Rex began its journey to the near-Earth asteroid Banu to collect a sample of rocks and dust from the surface. It was the first American mission to collect a sample from an asteroid. The spacecraft brought the sample, which weighed 121.6 grams, to Israel on September 24, 2023.

"The possibility to finally delve into the sample that OSIRIS-Rex brought back from us after all these years is very exciting," said Dante Loretta, principal investigator of OSIRIS-Rex. "This breakthrough answers long-standing questions about the early solar system and also opens up new possibilities to study the formation of the Earth as a habitable planet. The insights described in our review article aroused more curiosity and we are eager to continue researching."

Microscope image of a dark brown particle, about a millimeter long, with a light phosphate membrane. On the right is a smaller fragment that broke off. Credit: From Lauretta & Connolly et al. (2024) Meteoritics & Planetary Science, doi:10.1111/maps.14227
Microscope image of a dark brown particle, about a millimeter long, with a light phosphate membrane. On the right is a smaller fragment that broke off. Credit: From Lauretta & Connolly et al. (2024) Meteoritics & Planetary Science, doi:10.1111/maps.14227

Analysis of the sample from its structure has revealed intriguing insights into the asteroid's composition. The sample, dominated by clay minerals and especially serpentine, reflects the type of rock found in the ridges in the middle of the Earth's oceans, where material from the mantle, the layer below the Earth's crust, meets the water.

This interaction between ocean water and materials from the mantle results in the formation of clay and a variety of minerals, including carbonates, iron oxides and iron sulfide. But the most unexpected discovery in the Benno sample is the presence of water-soluble phosphates, Loretta said. These compounds are components of biochemistry in all life forms known today on Earth.

A similar phosphate was found in a sample from the asteroid Ryogo brought back by Japan's Hayabusa2 mission in 2020. But the magnesium sodium phosphate found in the sample is notable for its lack of encapsulations, which are like small bubbles of other minerals trapped inside the rock, and its grain size, unprecedented in any meteorite sample, Loretta said.

Finding magnesium sodium phosphate in a sample from Bennu raises questions about the geochemical processes that brought these elements together, and provides important clues about Bennu's historical conditions.

"The presence and condition of the phosphates, along with other elements and compounds in Beno, suggest that there was water in the asteroid's past," Loretta said. "It is possible that his son was once part of a wetter world, but this hypothesis requires further research."

This mosaic of his son was created using observations by the OSIRIS-Rex spacecraft that was close to the asteroid for more than two years. Credit: NASA/Goddard/University of Arizona
This mosaic of his son was created using observations by the OSIRIS-Rex spacecraft that was close to the asteroid for more than two years. Credit: NASA/Goddard/University of Arizona

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