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 & Planetary Science, doi:10.1111/maps.14227
NASA‘S OSIRIS-REx mission returned a sample from asteroid Bennu, revealing that it contains important solar system materials and possible signs of a watery past. This discovery provides valuable insights into the conditions of the early solar system and the possible origins of life.
An in-depth analysis of the rock and dust sample brought back from the nearby asteroid Bennu by NASA’s University of Arizona-led OSIRIS-REx mission has revealed some long-awaited surprises.
Bennu contains the original ingredients that formed our solar system, the OSIRIS-REx Sample Analysis Team discovered. 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 came as 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.
NASA’s OSIRIS-REx sample return capsule is seen shortly after landing in the desert on Sept. 24, 2023, at the Department of Defense’s Utah Test and Training Range. The sample was collected from the asteroid Bennu in October 2020 by NASA’s OSIRIS-REx spacecraft. Credit: NASA/Keegan Barber
Travel and delivery of the Bennu sample
The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer spacecraft, called OSIRIS-REx, launched on September 8, 2016, and began its journey to the nearby asteroid Bennu to collect a sample of rocks and dust from its surface. OSIRIS-REx was the first U.S. mission to collect a sample from an asteroid. The spacecraft delivered the sample, weighing 4.3 ounces, or 121.6 grams, to Earth on September 24, 2023.
“Finally having the chance to dive into the OSIRIS-REx sample from Bennu after all these years is incredibly exciting,” said Dante Lauretta, principal investigator for OSIRIS-REx and Regents 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 investigating the formation of Earth as a habitable planet. The insights outlined in our review paper have sparked further curiosity and fueled our eagerness to investigate more deeply.”
Lauretta is co-lead author of a paper published in Meteoritics and planetary science describing the nature of the asteroid sample. The article also serves as an introduction to the Bennu Sample Catalog, an online resource where information about the sample is made public 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 chair of the Division 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 what stories have yet to be told about the origins of our planet and life on it through the Bennu grains already in our laboratories.”
An overhead view of one of the containers holding rocks and dust from asteroid Bennu, with hardware scale marked in centimeters. Credit: NASA/Erika Blumenfeld and Joseph Aebersold
A ‘watery past’ for Bennu?
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 between ocean water and materials from the Earth’s mantle results in clay formation and gives rise to a variety of minerals, including carbonates, iron oxides and iron sulfides. But the most unexpected discovery in the Bennu sample is 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 2020 in the asteroid Ryugu sample delivered by the Japanese space agency’s Hayabusa2 mission. But the magnesium sodium phosphate found in the Bennu sample is notable for its lack of inclusions, which resemble tiny bubbles of other minerals trapped in the rock, and for the size of its grains, which is unprecedented in a meteorite sample, Lauretta said.
The discovery of magnesium sodium phosphates in the Bennu sample raises questions about the geochemical processes that brought these elements together and provides valuable clues about historical conditions on Bennu.
“The presence and abundance of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” Lauretta said. “Bennu may once have been part of a wetter world. However, this hypothesis requires further investigation.”
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
From a young solar system
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.
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 remained in their original state, having neither melted nor re-solidified since they formed, confirming their pristine nature and ancient origins.
This artist’s concept shows the OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security – Regolith Explorer) spacecraft making contact with the 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
Tips for the building blocks of life
The team also confirmed that the asteroid is rich in carbon and nitrogen. These elements are key to understanding the environments from which Bennu’s materials originated 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.”
What’s next
In the coming months, dozens of other labs 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 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 the paper’s co-lead author, Harold Connolly, the mission sample scientist who leads the Sample Analysis Team, a professor at Rowan University in Glassboro, New Jersey, and a visiting scholar at the UArizona. “Every week, analysis by the OSIRIS-REx Sample Analysis Team is yielding new and sometimes surprising findings that are helping to provide important constraints on the origin and evolution of Earth-like planets.”
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