A micrograph of a dark Bennu particle, about a millimeter long, with a crust of bright phosphate. A smaller fragment that has broken off is visible on the right. Credit: From Lauretta & Connolly et al. (2024) Meteoritics and planetary sciencedoi:10.1111/maps.14227
Analysis of a sample from the asteroid Bennu has revealed essential components of life and hints of a watery past, providing insight into the origins of the solar system and prebiotic chemistry.
- Early analysis of the asteroid Bennu sample collected by NASA‘S OSIRIS-REx mission has revealed dust rich in carbon, nitrogen and organic compounds, all essential components for life as we know it. The sample, dominated by clay minerals, particularly serpentine, reflects the type of rocks found at mid-ocean ridges on Earth.
- The magnesium-sodium phosphate found in the sample suggests that the asteroid may have split off from an ancient, small, primitive ocean world. The phosphate was a surprise to the team, as the mineral had not been detected by the OSIRIS-REx spacecraft at Bennu.
- While a similar phosphate was found in the asteroid Ryugu sample collected by JAXADuring the Japanese space agency’s Hayabusa2 mission in 2020, the magnesium-sodium phosphate found in the Bennu sample stood out for its purity (that is, the absence of other materials in the mineral) and the size of its grains, unprecedented in a meteorite sample.
This mosaic of Bennu was created using observations from NASA’s OSIRIS-REx spacecraft, which spent more than two years near the asteroid. Credit: NASA/Goddard/University of Arizona
Discoveries about the composition of asteroid Bennu
Scientists have been eagerly awaiting the chance to dig into the 4.3-ounce (121.6-gram) pristine asteroid Bennu sample collected by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer) mission since it arrived on Earth last fall. They hoped the material would hold secrets about the solar system’s past and the prebiotic chemistry that may have led to the origins of life on Earth. An early analysis of the Bennu sample, published recently in Meteoritics and planetary scienceshows that this 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 magnesium-sodium phosphate, which was a surprise to the research team because it was not seen in the remote sensing data collected by the spacecraft on Bennu. Its presence in the sample suggests that the asteroid may have split off from a long-vanished, small, primitive ocean world.
A view of eight sample trays containing the final material from the asteroid Bennu. The dust and rocks were poured into the trays from the top plate of the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) header. 51.2 grams were collected from this pour, bringing the final mass of the asteroid sample to 121.6 grams. Credit: NASA/Erika Blumenfeld & Joseph Aebersold
Analysis of the Bennu sample yielded intriguing insights into the asteroid’s composition. The sample is dominated by clay minerals, particularly serpentine, and reflects the type of rock found at Earth’s mid-ocean ridges, where material from the mantle, the layer beneath the Earth’s crust, encounters water.
This interaction not only results in the formation of clay; it also results in the formation of various minerals such as 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 for all known life on Earth today.
While a similar phosphate was found in the asteroid Ryugu sample delivered in 2020 by JAXA’s (Japan Aerospace Exploration Agency) Hayabusa2 mission, 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 the size of its grains, unprecedented in a meteorite sample.
A small portion of the asteroid Bennu sample brought back by NASA’s OSIRIS-REx mission, shown in microscope images. The top left panel shows a dark Bennu particle, about a millimeter long, with an outer crust of bright phosphate. The other three panels show progressively zoomed-in views of a fragment of the particle that split away along a bright phosphate vein, captured by a scanning electron microscope. Credit: From Lauretta & Connolly et al. (2024) Meteoritics and planetary sciencedoi:10.1111/maps.14227
The discovery of magnesium-sodium phosphates in the Bennu sample raises questions about the geochemical processes that concentrated these elements and provides valuable clues about historical conditions on Bennu.
“The presence and status of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” said Dante Lauretta, co-lead author of the paper and principal investigator for OSIRIS-REx at the University of Arizona, Tucson. “Bennu could once have been part of a wetter world. However, this hypothesis requires further investigation.”
“OSIRIS-REx gave us exactly what we were hoping for: a large, pristine asteroid sample, rich in nitrogen and carbon, from a formerly wet world,” said Jason Dworkin, a co-author of the paper and an OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
NASA’s OSIRIS-REx spacecraft leaves the surface of asteroid Bennu after collecting a sample. Credit: NASA’s Goddard Space Flight Center/CI Lab/SVS
Despite the possible interaction with water, Bennu remains a chemically primitive asteroid, with elemental ratios very similar to those of the Sun.
“The sample we brought back is currently 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 remained in their pristine state, having neither melted nor re-solidified since their formation, confirming their ancient origins.
The team confirmed that the asteroid is rich in carbon and nitrogen. These elements are key to understanding the environments from which Bennu’s materials originate and the chemical processes that transform simple elements into complex molecules, potentially laying the foundation for life on Earth.
“These findings underscore the importance of collecting and studying material from asteroids like Bennu — particularly low-density material that normally burns up as it enters Earth’s atmosphere,” Lauretta said. “This material is key to unraveling the intricate processes that formed the solar system and the prebiotic chemistry that may have helped give rise to life on Earth.”
In the coming months, dozens of other laboratories in the United States and around the world will receive portions of the Bennu sample from NASA’s Johnson Space Center in Houston. In addition, many more scientific papers describing analyses of the Bennu sample are expected from the OSIRIS-REx Sample Analysis Team in the coming years.
“The Bennu samples are tantalizingly beautiful alien rocks,” said Harold Connolly, co-lead author of the paper and OSIRIS-REx mission sample scientist at Rowan University in Glassboro, New Jersey. “Every week, analysis by the OSIRIS-REx Sample Analysis Team is producing new and sometimes surprising findings that are helping to provide important constraints on the origin and evolution of Earth-like planets.”
The OSIRIS-REx spacecraft was launched on September 8, 2016, and traveled to the nearby asteroid Bennu, collecting 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.
Reference: “Asteroid (101955) Bennu in the Lab: Properties of the Sample Collected by OSIRIS-REx” by Dante S. Lauretta, Harold C. Connolly, Joseph E. Aebersold, Conel M. O’D. Alexander, Ronald-L. Ballouz, Jessica J. Barnes, Helena C. Bates, Carina A. Bennett, Laurinne Blanche, Erika H. Blumenfeld, Simon J. Clemett, George D. Cody, Daniella N. DellaGiustina, Jason P. Dworkin, Scott A. Eckley, Dionysis I. Foustoukos, Ian A. Franchi, Daniel P. Glavin, Richard C. Greenwood, Pierre Haenecour, Victoria E. Hamilton, Dolores H. Hill, Takahiro Hiroi, Kana Ishimaru, Fred Jourdan, Hannah H. Kaplan, Lindsay P. Keller, Ashley J. King, Piers Koefoed, Melissa K. Kontogiannis, Loan Le, Robert J. Macke, Timothy J. McCoy, Ralph E. Milliken, Jens Najorka, Ann N. Nguyen, Maurizio Pajola, Anjani T. Polit, Kevin Righter, Heather L. Roper, Sara S. Russell, Andrew J. Ryan, Scott A. Sandford, Paul F. Schofield, Cody D. Schultz, Laura B. Seifert, Shogo Tachibana, Kathie L. Thomas-Keprta, Michelle S. Thompson, Valerie Tu, Filippo Tusberti, Kun Wang, Thomas J. Zega, CWV Wolner and , June 26, 2024, Meteoritics and planetary science.
DOI: 10.1111/kaarten.14227
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, 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 flight operations. Goddard and KinetX Aerospace were responsible for OSIRIS-REx spacecraft navigation. Curation for OSIRIS-REx is at NASA Johnson. International partnerships for this mission include the Canadian Space Agency’s (CSA) OSIRIS-REx Laser Altimeter instrument and collaboration on asteroid sample science 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.