On September 24, 2023, NASA’s OSIRIS-REx spacecraft dropped a capsule to Earth containing pristine carbonaceous regolith collected from the near-Earth asteroid Bennu. These samples were obtained after the probe made an impressive seven-year round trip through the solar system and back.
Since these pieces of space rock arrived (approximately 120 grams of sample, to be precise), scientists have eagerly awaited an analysis of the specimens that could tell us what molecules are inside Bennu. They hoped to find clues about the history of our solar system, since Bennu must have been present when our cosmic neighborhood was coming together, and prebiotic molecules that could provide information about the origin of life on Earth. It’s possible, many experts have speculated, that these samples could contain seeds of other essential ingredients, like water, that could have contributed to Earth’s habitability if they also ended up on our planet.
“The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now,” said Dante Lauretta, co-lead author of the paper and OSIRIS-REx principal investigator at the University of Arizona in Tucson, in a statement. declaration.
Although initial studies did indicate that the OSIRIS-REx samples displayed evidence of carbon and waterPerhaps even more notable is the team’s recent and unexpected discovery of magnesium-sodium phosphate. This is an ionic compound composed of the magnesium cation (Mg2+) and the phosphate anion (PO43-).
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On Earth, magnesium-sodium phosphate can be found in certain minerals and geological formations, as well as in living organisms, where it is present in various biochemical processes and is a component of bones and teeth. According to a NASA press release, however, its presence on Bennu surprised the research team because it was not seen in remote sensing data from the OSIRIS-REx spacecraft prior to sample collection. The team says its presence “suggests that the asteroid may have broken off from a tiny, primitive, long-vanished oceanic world.”
“The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” Lauretta said. “Bennu potentially could have been part of a wetter world. Although this hypothesis requires further investigation.”
The OSIRIS-REx spacecraft obtained a sample of Bennu’s regolith on October 20, 2020 using its Touch-and-Go Sample Acquisition Mechanism (TAGSAM), which comprises a specialized sampling head situated on an articulated arm. Bennu is a small B-type asteroid, which are relatively uncommon carbonaceous asteroids. “[Bennu] was selected as the mission target in part because telescopic observations indicated a primitive carbonaceous composition and water-bearing minerals,” the team stated in their paper.
The sample was collected at a site nicknamed Nightingale, situated in the Hokioi crater, an impact feature in Bennu’s northern hemisphere about 20 meters (66 feet) in diameter.
Further analysis of the samples revealed that the predominant component of the regolith sample is magnesium-containing phyllosilicates, mainly serpentine and smectite – rock types typically found at Earth’s mid-ocean ridges. A comparison of these serpentinites with their terrestrial counterparts provides possible insights into Bennu’s geological past. “Offering clues about the aqueous environment from which they originated,” the team wrote.
Although Bennu’s surface may have been altered by water over time, it still preserves some of the ancient features that scientists believe were present during the early days of the solar system. Bennu’s surface materials still contain some original features of the cloud of gas and dust from which the planets of our solar system 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.
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“These discoveries underscore the importance of collecting and studying material from asteroids like Bennu – especially low-density material that would normally burn up upon entering Earth’s atmosphere,” said Lauretta. “This material holds the key to unlocking the intricate processes of solar system formation and the prebiotic chemistry that could have contributed to the emergence of life on Earth.”
In addition to the important scientific discoveries made during this mission, it highlights the importance of returning samples to uncover the geological and geochemical intricacies of asteroids like Bennu, and their implications for the formation and evolution of the solar system.
“The data we present here are just the tip of the iceberg: there is likely more about the sample we don’t know than we know,” the scientists concluded.
