Surprising asteroid sample reveals Bennu may have originated from an ocean world

By Ashley Strickland, CNN

(CNN) — An early analysis of a sample collected from the asteroid Bennu suggests that the space rock had an unexpectedly water-rich past — and it may have even splintered off from an ancient ocean world.

The NASA OSIRIS-REx mission scooped up the 4.3-ounce (121.6-gram) pristine sample from the near-Earth asteroid in 2020 and returned it to Earth last September.

Since then, scientists have been analyzing the asteroid’s rocks and dust to see what secrets they may contain about the asteroid’s composition and whether it could have delivered the elements for life to Earth. Asteroids also intrigue scientists because they are the leftover remnants from the formation of the solar system.

An initial review of some of the sample, shared in October, suggested that the asteroid contained a large amount of carbon.

During a new analysis of the sample, the team discovered that Bennu’s dust is rich in carbon, nitrogen and organic compounds, all of which helped form the solar system. These ingredients are also essential to life as we understand it and could help scientists better understand how Earth-like planets evolve.

A study detailing the findings appeared Wednesday in the journal Meteoritics & Planetary Science.

“OSIRIS-REx gave us exactly what we hoped: a large pristine asteroid sample rich in nitrogen and carbon from a formerly wet world,” said study coauthor Jason Dworkin, OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

The elements for life

The biggest surprise was finding magnesium-sodium phosphate within the sample, which remote sensing didn’t initially detect when OSIRIS-REx, or the Origins, Spectral Interpretation, Resource Identification, and Security — Regolith Explorer mission, was orbiting Bennu.

Magnesium-sodium phosphate is a compound that can be dissolved in water and serves as a component of biochemistry for life.

It’s possible that the asteroid may have broken away from a tiny, primitive ocean world that no longer exists in our solar system, the researchers said.

The asteroid’s sample largely consists of clay minerals, including serpentine, which makes the sample remarkably similar to rocks found at midocean ridges on Earth. These ridges are where material from the mantle, the layer beneath Earth’s surface crust, encounters water.

A similar phosphate was found in a sample from the asteroid Ryugu collected by the Japan Aerospace Exploration Agency’s Hayabusa2 mission and returned to Earth in December 2020. But the compound from the Bennu sample is purer and has larger grains.

“The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” said co-lead study author Dante Lauretta, principal investigator for OSIRIS-REx and regents professor at the University of Arizona, Tucson, in a statement. “Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation.”

Cosmic time capsules

The rocks collected from Bennu represent a time capsule from the early days of the solar system dating back more than 4.5 billion years.

“The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now,” Lauretta said.

Astronomers believe that space rocks such as asteroids and comets may have served as ancient messengers in our solar system.

“This means asteroids such as this may have played a key role in delivering water and the building blocks of life to Earth,” said study coauthor Nick Timms, OSIRIS-REx Sample Analysis team member and associate professor in Curtin University’s School of Earth and Planetary Sciences, in a statement.

If these smaller rocky bodies were carrying water, minerals and other elements and crashed into Earth as it was forming billions of years ago, they could have helped set the stage for life to begin on our planet.

“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,” Lauretta said. “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.”

The wealth of material collected from the asteroid means that more labs around the world will receive their own pieces of the sample to study.

“The Bennu samples are tantalizingly beautiful extraterrestrial rocks,” said co-lead study author Harold Connolly Jr., OSIRIS-REx mission sample scientist and chair of the department of geology at Rowan University’s School of Earth & Envrionment in Glassboro, New Jersey, in a statement. “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.”

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