The sample return capsule from NASA’s OSIRIS-REx mission shortly after touching down in the desert, Sunday, Sept. 24, 2023, in Utah. The sample sealed inside has surprised scientist who have only begun to analyze it. Credit: NASA/Keegan Barber
The parent of Bennu was deep in the solar system, held many of the building blocks of life, and likely contained salty brines below the surface.
On a clear September morning in 2023, a small capsule streaked through Earth’s atmosphere, parachuting down into the Utah desert. Burnished to a dull black from its fiery descent, the capsule contained a pristine sample of rock and dust that startled scientists—not just because there was so much of it, or that the capsule was so difficult to open, but also because it contained a surprising array of the building blocks of life.
NASA’s OSIRIS-REx spacecraft had traveled more than one billion miles over seven years to reach this moment, successfully delivering a pristine sample of Bennu, a rubble-pile asteroid. At 1,614 ft. in diameter, the carbon-rich asteroid is probably a shattered remnant from a much larger body that broke into pieces during a violent collision as much as 2 billion years ago.
Curation teams process the sample return capsule from NASA’s OSIRIS-REx mission in a cleanroom, Sunday, Sept. 24, 2023, at the Department of Defense’s Utah Test and Training Range. Credit: NASA/Keegan Barber
“The OSIRIS-REx team discovered that Bennu contains many precursor building blocks of life, along with the evidence that it comes from an ancient, wet world and contains materials that point to Bennu having traveled from the coldest regions of the solar system that are likely beyond Saturn’s orbit,” said Nicky Fox, Associate Administrator of NASA’s Science Mission Directorate, speaking at a recent NASA press conference.
“Their findings do not show evidence of life itself, but they do suggest that the conditions necessary for the emergence of life were likely widespread across the early solar system,” Fox said.
The event highlighted recent research papers published in the journals Nature and Nature Astronomy. In the Nature Astronomy paper, scientists found that the mission’s pristine samples, sealed in space and opened in a special clean room on Earth, were especially rich in volatiles, containing more carbon, nitrogen, and ammonia than has been observed in most meteorites. Isotopic analysis suggests that ammonia and other nitrogen-containing molecules originated in the extreme cold of a distant molecular cloud or outer protoplanetary disk.
The sample from Bennu includes 14 of the 20 amino acids used by life on Earth to make proteins, along with five nucleobases that form the genetic instructions in DNA and RNA. Additionally, the sample contains a high abundance of ammonia, a critical component in biological chemistry. Scientists also detected formaldehyde, which reacts with ammonia to form complex molecules such as amino acids.
In the Nature paper, a team found an array of salt minerals that point to the evaporation of an ancient brine. These diverse salts quickly degrade with exposure to Earth’s atmosphere, so NASA’s careful handling of the OSIRIS-REx sample was key to this discovery. It suggests that these salts formed through the evaporation of a late-stage brine that existed early in the history of Bennu’s parent body.
A top-down 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
Tim McCoy, curator of meteorites at the Smithsonian Institution and deputy mission sample scientist, explained that Bennu “…came from an ancestral asteroid of rock and ice that broke apart … early in the history of the solar system. That ice melted by the radioactive decay of elements, and the reaction of the water with the rock produced minerals like clays and sulfides, iron oxides and carbonate minerals that we’ve seen before in meteorites.”
“But there was a surprise,” McCoy said. “And that surprise was that we found a whole set of minerals that are really rich in sodium—carbonates and phosphates and sulfates, chlorides and fluorides.”
McCoy said that although these sodium minerals haven’t been seen in meteorites before, they are common in Earth’s deserts. “They’re actually reasonably well known where sodium-rich lakes [such as] Searles Lake in California, in the Mojave, through evaporation form these sodium rich brines, salt-rich layers. And as those evaporate, they become increasingly concentrated in things like sodium and chlorine and fluorine.”
In this video frame, Jason Dworkin holds up a vial that contains part of the sample from asteroid Bennu. Dworkin is the mission’s project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Credit: NASA/James Tralie
McCoy thinks it’s unlikely that Bennu’s ancestral asteroid had significant water on the surface. Rather that melting ice left a muddy exterior with interior pockets or veins of fluid. As the water evaporated or was drawn away from the pockets, these minerals were left behind. And when the asteroid broke apart 2 billion years ago, those pockets were in the material that became Bennu.
This discovery has broader implications. Because the asteroid doesn’t appear to be especially unique, it suggests that the elements that gave rise to life on Earth could have been widespread across the early solar system. The findings also support the theory that asteroids like Bennu could have played a role in seeding Earth with some of the chemical building blocks of life.
Similar minerals have been detected recently on the dwarf planet Ceres and Saturn’s moon Enceladus, where plumes of material containing sodium carbonate have been observed erupting from beneath the surface.
NASA will preserve 70 percent of the 121.6 g Bennu sample at the Johnson Space Center, where it will be available for scientists worldwide and for future generations. Lessons learned from the Apollo Moon missions have shown the value of long-term sample storage, as scientific techniques continue to evolve. A portion of the Bennu sample is being stored at -80 degrees Celsius (-110°F) to ensure its integrity for decades, or even centuries, to come.
“These samples provide a unique opportunity to explore prebiotic chemistry that occurred in the solar system before life emerged on Earth,” said Danny Glavin, a senior scientist at NASA’s Goddard Space Flight Center who is leading the Sample Organics Analysis Working Group on the mission.
To learn more about the OSIRIS-REx mission and the sample collected, click here.
