Microscope image of a dark Bennu particle, about a millimeter long, with a crust of bright phosphate. On the right is a smaller fragment that broke off. Credit: From Lauretta & Connolly et al. (2024) Meteoritics and Planetary Science, doi:10.1111/maps.14227
NASA‘c OSIRIS-REX The mission returned a sample of asteroid Bennu, revealing that it contains key solar system materials and possible signs of a watery past. This discovery provides valuable insight into the conditions of the early solar system and the potential origin of life.
A deep dive into the rock and dust sample returned from the near-Earth asteroid Bennu by the OSIRIS-REx mission led by NASA’s University of Arizona revealed some long-awaited surprises.
Bennu contains the original ingredients that formed our solar system, the OSIRIS-REx sample analysis team found. The asteroid 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 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.
The sample return capsule of NASA’s OSIRIS-REx mission is seen shortly after landing in the desert on September 24, 2023 at the Department of Defense Test and Training Range in Utah. The sample was taken from asteroid Bennu in October 2020 by NASA’s OSIRIS-REx spacecraft. Credit: NASA/Keegan Barber
Travel and delivery of the Bennu sample
Launched on September 8, 2016, the Origins, Spectral Interpretation, Resource Identification and Security–Regolith Explorer spacecraft, called OSIRIS-REx, began its journey to the near-Earth asteroid Bennu to collect a sample of rocks and dust from the surface. OSIRIS-REx was the first US mission to sample an asteroid. The spacecraft delivered the sample weighing 4.3 ounces, or 121.6 grams, to Earth on September 24, 2023.
“Finally having the opportunity to dig into the OSIRIS-REx sample from Bennu after all these years is incredibly exciting,” said Dante Lauretta, OSIRIS-REx principal investigator and professor of planetary sciences at the University of Arizona Lunar and Planetary laboratory. “This breakthrough not only answers long-standing questions about the early solar system, but also opens new avenues for studying the formation of Earth as a habitable planet. The insights outlined in our review paper sparked further curiosity, stimulating our desire to explore further.”
Lauretta co-authored an article published in Meteoritics and Planetary Sciences which describes the nature of the asteroid sample. The paper also serves as an introduction to the Bennu sample catalog, an online resource where sample information is publicly available and where scientists can request sample material for their own research.
“The publication of the first paper led by Dr. Lauretta and Dr. Connolly describing the Bennu sample is an exciting milestone for the mission and for the Lunar and Planetary Laboratory,” said Mark Marley, director of the UArizona Lunar and Planetary Laboratory and head of the Department of Planetary Sciences. “Our faculty, scientists and students will continue to study the sample for years and decades to come.” For now, we can only imagine the stories of our planet’s origins and life on it yet to be told by the Bennu grains already in our laboratories.
A top-down view of one of the containers containing rocks and dust from asteroid Bennu, with a hardware scale marked in centimeters. Credit: NASA/Erika Blumenfeld and Joseph Ebersold
A ‘watery past’ for Bennu?
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 between ocean water and materials from Earth’s mantle results in the formation of clay and gives rise to a variety of minerals, including carbonates, iron oxides, and iron sulfides. But the most unexpected finding in the Bennu sample was the presence of water-soluble phosphates, Lauretta said. These compounds are components of the biochemistry for all known life on Earth today.
A similar phosphate was found in the Ryugu asteroid sample delivered by the Japan Aerospace Exploration Agency’s Hayabusa2 mission in 2020. But the magnesium-sodium phosphate found in the Bennu sample stands out for its lack of inclusions, which are like tiny bubbles of other minerals , trapped inside the rock and its grain size, unprecedented in any meteorite sample, Lauretta said.
The finding of magnesium-sodium phosphates in the Bennu sample raises questions about the geochemical processes that brought these elements together and provides valuable clues about Bennu’s historical conditions.
“The presence and state of the phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” Lauretta said. “Bennu could potentially have once been part of a wetter world. However, this hypothesis requires further investigation.
This Bennu mosaic was created using observations made by NASA’s OSIRIS-REx spacecraft, which was in close proximity to the asteroid for more than two years. Credit: NASA/Goddard/University of Arizona
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.
The asteroid’s composition offers a glimpse into the early days of our solar system, more than 4.5 billion years ago. The rocks have retained their original state, having neither melted nor solidified since their creation, confirming their pristine nature and ancient origins.
This artist’s concept shows the OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security – Regolith Explorer) spacecraft in contact with asteroid Bennu with the Touch-And-Go Sample Arm Mechanism, or TAGSAM. The mission successfully returned a sample of Bennu’s surface coating to Earth for study. Credit: NASA
Hints at the building blocks of life
The team also confirmed that the asteroid is rich in carbon and nitrogen. These elements are critical to understanding the environment from 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 normally burns up upon entering Earth’s atmosphere,” Lauretta said. “This material holds the key to unraveling the complex processes of solar system formation and the chemistry of prebiotics that could 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 the Bennu sample are expected in the next few years from the OSIRIS-Sample Analysis Team REx.
“The Bennu samples are tantalizingly beautiful alien rocks,” said the paper’s co-author, Harold Connelly, a sample mission scientist who led the sample analysis team, a professor at Rowan University in Glassboro, New Jersey, and a visiting researcher at the University of Arizona. “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.”
Reference: “Asteroid (101955) Bennu in the laboratory: Properties of the sample collected by OSIRIS-REx” by Dante S. Lauretta, Harold S. Connelly, Joseph E. Abersold, Connell 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, Pierce Koefoed, Melissa K. Kontogiannis, Loan Le, Robert J. McCoy, Timothy J. McCoy, Ralph E. Milliken, Jens Nyorka, Ann N. Nguyen, Maurizio Paiola, Anjani T. Pollitt, Kevin Reiter, Heather L. Roper, Sarah S. Russell, Andrew J. Ryan, Scott A. Sandford, Paul F. Scofield, Cody D. Schultz, Laura B. Seifert, Shogo Tachibana, Kathy L. Thomas-Keprta, Michelle S. Thompson, Valerie Tu, Filippo Tusberti, Kun Wang, Thomas J. Zega , CWV Wolner and , 26 June 2024 Meteoritics and Planetary Sciences.
DOI: 10.1111/maps.14227
