On September 24, 2023, NASA’s OSIRIS-REx spacecraft dropped a capsule on Earth containing pristine carbonaceous regolith collected from the near-Earth asteroid Bennu. These samples were obtained after the probe completed an impressive seven-year tour of the solar system and back.
Since these pieces of space rock arrived (about 120 grams of sample, to be precise), scientists have eagerly awaited an analysis of the specimens that could tell us which molecules are in Bennu. They hoped to find clues about the history of our solar system, since Bennu should have been present when our cosmic neighborhood converged, and prebiotic molecules that could provide insight into the origins of life on Earth. It’s possible, many experts speculated, that these samples could contain the seeds of other essential ingredients, such as water, that could have contributed to Earth’s habitability if they had also landed on our planet.
“The sample we returned is the largest reservoir of unaltered asteroid material on Earth today,” Dante Lauretta, co-lead author of the paper and principal investigator of OSIRIS-REx at the University of Arizona, Tucson, said in a study. rack.
While initial investigations indeed pointed to the OSIRIS-REx samples showed evidence of carbon and waterPerhaps even more remarkable is the team’s recent and unexpected discovery of magnesium sodium phosphate. This is an ionic compound consisting of the magnesium cation (Mg2+), the sodium cation (Na⁺) and the phosphate anion (PO43-).
Related: NASA’s OSIRIS-REx lands samples from asteroid Bennu on Earth after historic 6 billion kilometer journey
On Earth, magnesium sodium phosphate can be found in certain minerals and geological formations. However, according to a NASA press release, the probe’s presence on Bennu surprised the research team, as it was not seen in the OSIRIS-REx probe’s remote sensing data prior to sample collection. The team says its presence “indicates that the asteroid could have split off from a long-ago, small, primitive ocean world.”
“The presence and state of phosphates, along with other elements and compounds on Bennu, indicate a watery past for the asteroid,” Lauretta says. “Bennu could once have been part of a wetter world, although this hypothesis requires further research.”
The OSIRIS-REx spacecraft acquired a sample of Bennu’s regolith on October 20, 2020, using the Touch-and-Go Sample Acquisition Mechanism (TAGSAM), which consists of a specialized sample head located on an articulated arm. Bennu is a small B-type asteroid, relatively uncommon carbonaceous asteroids. “[Bennu] was chosen as a mission target in part because telescopic observations indicated a primitive, carbonaceous composition and hydrous minerals,” the team said in their paper.
The sample was collected at a site nicknamed Nightingale, located in the Hokioi Crater, an impact feature in Bennu’s northern hemisphere with a diameter of about 20 meters (66 feet).
Further analysis of the samples revealed that the predominant component of the regolith sample consists of magnesium-bearing phyllosilicates, mainly serpentine and smectite – rock types commonly found at Earth’s mid-ocean ridges. A comparison of these serpentinites with their terrestrial counterparts offers possible insights into Bennu’s geological past. “It provides clues about the aqueous environment from which they originated,” the team wrote.
Although Bennu’s surface has been altered by water over time, it still retains some of the ancient features that scientists believe were present in the early days of the solar system. Bennu’s surface materials still contain some of the original features of the cloud of gas and dust from which our solar system’s planets formed — known as the protoplanetary disk.
The team’s study also confirmed that the asteroid is rich in carbon, nitrogen and some organic compounds – all of which, in addition to magnesium phosphate, are essential components for life as we know it on Earth.
“These findings underscore the importance of collecting and studying material from asteroids like Bennu — especially low-density material that would normally burn up as it enters Earth’s atmosphere,” Lauretta says. “This material holds the key to unraveling the complicated processes of solar system formation and the prebiotic chemistry that could have contributed to the origins of life on Earth.”
In addition to the important scientific discoveries made during this mission, it also underlines the importance of returning samples for unraveling the geological and geochemical complexity of asteroids like Bennu and their implications for the formation and evolution of the Solar System.
“The data we have presented here is just the tip of the iceberg: there is likely more about the sample that we don’t know than we do know,” the scientists concluded.
The article about these results was published on June 26 in the journal Meteoritics & Planetary Science.
Editorial update 6/27: Magnesium phosphate, and not magnesium sodium phosphate, is present in living organisms. This article has been updated to reflect that.