Surprising discovery of phosphate in NASA’s OSIRIS-REx asteroid sample

Scientists have been eagerly awaiting the opportunity to excavate the intact 121.6-gram sample from asteroid Bennu collected by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security—Regolith Explorer) mission since its arrival on Earth last fall. They hope this material will hold secrets about the solar system’s past and the prebiotic chemistry that may have led to the origin of life on Earth.

A first analysis of the Bennu sample, published in Meteoritics and planetary sciencesdemonstrates that this enthusiasm was justified.

The OSIRIS-REx sample analysis team discovered that Bennu contains the original ingredients that formed our 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 sodium magnesium phosphate, which was a surprise to the research team because it was not detected in the remote sensing data collected by the spacecraft in Bennu. Its presence in the sample suggests that the asteroid may have split from a primitive, tiny, long-extinct ocean world.

A phosphate surprise

Analysis of the Bennu sample revealed intriguing information about the asteroid’s composition. Dominated by clay minerals, particularly serpentine, the sample reflects the type of rock found on Earth’s mid-ocean ridges, where materials from the mantle, the layer beneath the Earth’s crust, meet water.

This interaction not only results in the formation of clay; it also gives rise to a variety of minerals like carbonates, iron oxides and iron sulfides. But the most unexpected discovery is the presence of water-soluble phosphates. These compounds are components of the biochemistry of all known life on Earth today.

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

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

“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-senior author of the paper and principal investigator for OSIRIS-REx at the University of Arizona in Tucson. “Bennu could have been part of a wetter world, although this hypothesis requires further investigation.”

“OSIRIS-REx gave us exactly what we hoped 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 Goddard Space. Flight Center in Greenbelt, Maryland.

Of a young solar system

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

“The sample we returned currently constitutes the largest reservoir of unaltered asteroid material on Earth,” 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 retained their pristine state, having neither melted nor resolidified since their creation, thus affirming their ancient origins.

Clues to the Building Blocks of Life

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

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

And after

Dozens of additional laboratories across the United States and around the world 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 analyzes of the sample from Bennu are expected in the coming years. OSIRIS-REx sample analysis team.

“The Bennu samples are tantalizingly beautiful extraterrestrial rocks,” said Harold Connolly, co-senior author of the paper and sample scientist for the OSIRIS-REx mission at Rowan University in Glassboro, New Jersey. “Each week, the analysis performed by the OSIRIS-REx sample analysis team provides new, 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.