Early analysis of a sample of the asteroid Bennu returned by NASA’s OSIRIS-REx mission has revealed dust rich in carbon, nitrogen and organic compounds, all of which are essential components for life as we know it. The sample, dominated by clay minerals, particularly serpentine, reflects the type of rock found at mid-ocean ridges on Earth.
The sodium magnesium phosphate found in the sample hints that the asteroid may have broken away from an ancient, small, primitive ocean world. The phosphate was a surprise to the team because the mineral was not detected by the OSIRIS-REx spacecraft during its visit to Bennu.
While a similar phosphate was found in a sample of the asteroid Ryugu returned by the Hayabusa2 mission (JAXA) in 2020, the magnesium sodium phosphate found in the Bennu sample stands out for its purity (i.e. the absence of other materials making up the mineral) and its grain size, which is unprecedented for any meteorite sample.
Scientists have been eager to dig into a 4.3-ounce (121.6 grams) pristine sample of asteroid Bennu collected by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer) mission since it was returned to Earth last fall. They hoped the material would contain secrets about the solar system’s past and the prebiotic chemistry that may have led to life on Earth. An early analysis of the Bennu sample, published June 26 in Meteoritics & Planetary Science, suggests that excitement was justified.
The OSIRIS-REx sample analysis team found 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 for 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 at Bennu. Its presence in the sample suggests that the asteroid may have broken off from a long-lost, tiny, primitive ocean world.
Analysis of a sample of Bennu has revealed intriguing clues about the asteroid’s composition. The sample, which is dominated by clay minerals, particularly serpentine, reflects a type of rock found at mid-ocean ridges on Earth, where material from the mantle, the layer beneath the Earth’s crust, meets water.
This interaction does not simply produce clay; it also produces various minerals such as carbonates, iron oxides, and iron sulfides. But the most surprising 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 a sample of the asteroid Ryugu returned by the Hayabusa2 mission (JAXA) in 2020, the magnesium sodium phosphate found in the Bennu sample stands out for its purity (i.e. the absence of other materials in the mineral) and its grain size, which is unprecedented for any meteorite sample.
A tiny portion of a sample of asteroid Bennu returned by NASA’s OSIRIS-REx mission is shown in microscope images. The top left panel shows a dark particle of Bennu, about a millimeter long, with an outer crust of bright phosphate. The other three panels show progressively larger scanning electron microscope images of a fragment of the particle that has separated along a bright phosphate-containing vein. From Loretta and Connolly et al. (2024) Meteoritics and Planetary Science, doi:10.1111/maps.14227
The discovery of magnesium and sodium phosphates in the Bennu sample raises questions about the geochemical processes that concentrated these elements and provides valuable information about Bennu’s historical conditions.
“The presence and state of phosphates, as well as other elements and compounds, on Bennu suggests a watery past for the asteroid,” said Dante Lauretta, a co-author of the paper and principal investigator of OSIRIS-REx at the University of Arizona in Tucson. “Bennu could have potentially 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, a co-author of the paper and the OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Despite its possible history of interaction with water, Bennu remains a chemically primitive asteroid, with elemental proportions very similar to those of the Sun.
“The sample we returned is currently the largest reservoir of unaltered asteroid material on Earth,” Loretta 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 original state, without melting or re-solidifying since their formation, confirming their ancient origin.
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 formed and the chemical processes that transformed simple elements into complex molecules, potentially laying the foundation for life on Earth.
“These results highlight the importance of collecting and studying material from asteroids like Bennu — especially low-density material that would typically burn up upon entry into Earth’s atmosphere,” Loretta said. “This material holds the key to unraveling the complex processes that formed the solar system and the prebiotic chemistry that may have helped fuel the emergence of life on Earth.”
In the coming months, dozens more laboratories in the United States and around the world will receive portions of the Bennu sample from NASA’s Johnson Space Center in Houston, and more scientific papers describing the analysis of the Bennu sample are expected to appear in the next few years from the OSIRIS-REx sample analysis team.
“The Bennu samples are tantalizingly beautiful extraterrestrial rocks,” said Harold Connolly, a co-author of the paper and a project scientist for the OSIRIS-REx mission at Rowan University in Glassboro, New Jersey. “Every week, the OSIRIS-REx sample analysis team’s analysis yields new and sometimes surprising results that help establish 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 its surface. OSIRIS-REx, the first U.S. mission to collect a sample from an asteroid, returned the sample to Earth on September 24, 2023.
NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provided overall mission management, systems engineering, and safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona in Tucson is the principal investigator. The university leads the science team and plans the mission’s science observations and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft and provided mission control. Goddard and KinetX Aerospace provided navigation for the OSIRIS-REx spacecraft. NASA Johnson Space Center oversees OSIRIS-REx. International partnerships on the mission include the OSIRIS-REx laser altimeter from CSA and an asteroid sample science collaboration with JAXA’s Hayabusa2 mission. OSIRIS-REx is the third mission in NASA’s New Frontiers program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.