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Scientists eagerly awaited the opportunity to dig into the pristine 4.3-ounce (121.6-gram) asteroid Bennu sample collected by NASA’s OSIRIS-REx (Origin, Spectral Interpretation, Resource Identification and Security – Regolith Explorer) mission. since it was delivered to Earth last fall. They hope the material holds secrets from the solar system’s past and the prebiotic chemistry that may have led to the origin of life on Earth.

An early analysis of the Bennu sample published in Meteoritics and Planetary Sciencesshows that this excitement is justified.

The OSIRIS-REx sample analysis team found that Bennu contains the original ingredients that formed our solar system. The asteroid 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 contained magnesium sodium phosphate, which was a surprise to the research team as it was not seen in the remote sensing data collected by the Bennu spacecraft. Its presence in the sample suggests that the asteroid may have broken off from a long-extinct, small, primitive ocean world.

A phosphate surprise

Analysis of the Bennu sample has revealed intriguing insights into the asteroid’s composition. Dominated by clay minerals, particularly serpentine, the sample reflects the type of rock found at Earth’s mid-ocean ridges, where material from the mantle, the layer beneath the Earth’s crust, meets water.

This interaction not only results in the formation of clay; it also results in various minerals such as carbonates, iron oxides, and iron sulfides. But the most unexpected discovery was the presence of water-soluble phosphates. These compounds are components of the biochemistry for all known life on Earth today.

While a similar phosphate was found in the Ryugu asteroid sample delivered by JAXA’s (Japan Aerospace Exploration Agency) Hayabusa2 mission in 2020, the magnesium-sodium phosphate found in the Bennu sample stands out for its purity—that is, the absence of other materials in the mineral—and its grain size, unprecedented in any meteorite sample.

The finding of magnesium-sodium phosphates in the Bennu sample raises questions about the geochemical processes that concentrated these elements and provides valuable clues about the historical conditions of Bennu.

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

“OSIRIS-REx gave us exactly what we were hoping for: a large pristine asteroid sample rich in nitrogen and carbon from a once-wet world,” said Jason Dworkin, co-author of the paper and OSIRIS-REx project scientist at NASA’s Goddard Space Flight center in Greenbelt, Maryland.

From a young solar system

Despite its possible history of interaction with water, Bennu remains a chemically primitive asteroid, with rudimentary proportions closely resembling those of the Sun.

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

This composition offers a glimpse into the early days of our solar system, more than 4.5 billion years ago. These rocks have preserved their original state, having neither melted nor solidified since their creation, confirming their ancient origin.

Hints at the building blocks of life

The team confirmed that the asteroid is rich in carbon and nitrogen. These elements are critical to understanding the environment in which Bennu’s materials originated and the chemical processes that transform simple elements into complex molecules, potentially laying the foundations for life on Earth.

“These findings highlight the importance of collecting and studying material from asteroids like Bennu — especially low-density material that would normally burn up upon entering Earth’s atmosphere,” Lauretta said. “This material holds the key to unraveling the complex processes of solar system formation and the prebiotic chemistry that may have contributed to the emergence of life on Earth.”

What next

Dozens more laboratories in the United States and around the world will receive pieces of the Bennu sample from NASA’s Johnson Space Center in Houston in the coming months, and many more scientific papers describing analyzes of the Bennu sample are expected in the next few years by the Sample Analysis Team OSIRIS-REx.

“The Bennu samples are hauntingly beautiful alien rocks,” said Harold Connelly, co-author of the paper and OSIRIS-REx sample scientist at Rowan University in Glassboro, New Jersey. “Each week, analysis by the OSIRIS-REx sample analysis team provides new and sometimes surprising discoveries that help place important constraints on the origin and evolution of Earth-like planets.”

Launched on September 8, 2016, the OSIRIS-REx spacecraft traveled to the near-Earth asteroid Bennu and collected a sample of rocks and dust from the surface. OSIRIS-REx, the first US mission to collect a sample from an asteroid, delivered the sample to Earth on September 24, 2023.