Introduction
The discovery of magnesium-sodium phosphate in NASA’s OSIRIS-REx sample from asteroid Bennu suggests the asteroid may have originated from an ancient, small, primitive ocean world. This finding was unexpected since the OSIRIS-REx spacecraft had not detected this mineral while at Bennu.
Though a similar phosphate was found in the Ryugu asteroid sample from JAXA’s Hayabusa2 mission in 2020, the magnesium-sodium phosphate in the Bennu sample is remarkable for its purity and the unprecedented size of its grains compared to any other meteorite sample.
Sample Collection and Analysis
Scientists eagerly anticipated the arrival of the 4.3-ounce (121.6-gram) pristine Bennu sample, collected by NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security — Regolith Explorer) mission, since it was delivered to Earth last fall. They hoped the material would reveal secrets of the solar system’s past and the prebiotic chemistry that might have led to the origin of life on Earth. An early analysis of the Bennu sample, published on June 26 in Meteoritics & Planetary Science, shows this excitement was justified.
Key Discoveries
Original Ingredients of the Solar System
The original elements that created our solar system are found in Bennu, according to the OSIRIS-REx Sample Analysis Team which are rich in carbon and nitrogen as well as organic compounds—all vital ingredients for life as we know it—the dust of the asteroid reflects Magnesium-sodium phosphate, which was absent from the remote sensing data gathered by the spacecraft at Bennu, points to the asteroid perhaps having come from a long-gone, small, primordial ocean world.
Phosphate Surprise
Study of the Bennu sample yielded fascinating new understanding of the composition of the asteroid. Mostly composed of clay minerals—especially serpentine—the sample looks like rocks found on Earth’s mid-ocean ridges, where mantle material meets water. Apart from producing clay, this interaction generates several minerals including carbonates, iron oxides, and iron sulfides. Still, the most surprising find is the existence of phosphates soluble in water. Comprising elements of biochemistry for all known life on Earth today, these molecules
Although a similar phosphate was discovered in the Ryugu sample from JAXA’s Hayabusa2 mission in 2020, the magnesium-sodium phosphate found in the Bennu sample is notable for its purity and unparalleled grain size relative to any other meteorite sample. The presence of magnesium-sodium phosphates in the Bennu sample begs problems regarding the geochemical processes concentrated in these elements and provides important hints about the historical conditions of Bennu..
Insights and Implications
“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-lead author of the paper and principal investigator for OSIRIS-REx at the University of Arizona, Tucson. “Bennu potentially could have once been part of a wetter world. However, this hypothesis requires further investigation.”
“OSIRIS-REx gave us exactly what we hoped: a large pristine asteroid sample rich in nitrogen and carbon from a formerly wet world,” said Jason Dworkin, co-author of the paper and the OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
From a Young Solar System
Despite its potential history with water, Bennu remains a chemically primitive asteroid, with elemental proportions closely resembling those of the Sun. “The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now,” said Lauretta. This composition offers a glimpse into the early days of our solar system, over 4.5 billion years ago. These rocks have retained their original state, having neither melted nor resolved since their inception, affirming their ancient origins.
Hints at Life’s Building Blocks
The team has confirmed the presence of substantial quantities of carbon and nitrogen in the asteroid. Gaining knowledge about the sources of Bennu’s materials and the chemical reactions that resulted in the creation of intricate molecules is crucial for understanding the specific conditions in which these processes took place. These factors likely influenced the emergence of life on Earth. “These findings underscore the importance of collecting and studying material from asteroids like Bennu — especially low-density material that would typically burn up upon entering Earth’s atmosphere,” Lauretta emphasized. “This material holds the key to unraveling the intricate processes of solar system formation and the prebiotic chemistry that could have contributed to life emerging on Earth.”
What’s Next
In the coming months, dozens more labs in the United States and around the world will receive portions of the Bennu sample from NASA’s Johnson Space Center in Houston. Many more scientific papers describing analyses of the Bennu sample are expected in the next few years from the OSIRIS-REx Sample Analysis Team.
“The Bennu samples are tantalizingly beautiful extraterrestrial rocks,” said Harold Connolly, co-lead author of the paper and OSIRIS-REx mission sample scientist at Rowan University in Glassboro, New Jersey. “Each week, analysis by the OSIRIS-REx Sample Analysis Team provides new and sometimes surprising findings that are helping place important constraints on the origin and evolution of Earth-like planets.”
Launched on Sept. 8, 2016, the OSIRIS-REx spacecraft traveled to near-Earth asteroid Bennu and collected a sample of rocks and dust from the surface. OSIRIS-REx, the first U.S. mission to collect a sample from an asteroid, delivered the sample to Earth on Sept. 24, 2023.
Conclusion
The identification of magnesium-sodium phosphate in the sample collected by the OSIRIS-REx spacecraft from the asteroid Bennu offers valuable knowledge about the asteroid’s history of water presence and the process of solar system formation. These discoveries not only deepen our comprehension of Bennu’s past but also provide potential insights into the genesis of life on Earth. As additional examinations progress, scientists expect further discoveries that have the potential to fundamentally alter our understanding of the early solar system and the chemical mechanisms that facilitated the emergence of life.
