Asteroid Bennu not only held water at some point in its distant past but also contains briny residue that harbors some of the crucial building blocks for life, according to a team of scientists that studied samples of the space rock.
The brine contains compounds that have never been previously observed in asteroid samples, including compounds of sodium carbonate. The brine can also be distinguished from brine samples on Earth, as it is much richer in phosphorus—an element abundant on asteroids but uncommon on Earth. The team’s findings shake up the story of Bennu, whose rocky bits were valiantly collected by NASA in 2020, and hint at the ways life may have taken root from the chemical cocktail of the cosmos.
Two studies published today in Nature and Nature Astronomy reveal some of the first analyses done of the Bennu samples. The papers describe briny residue found in the samples, which differs from the composition of Earth’s brines, as well as protein-building amino acids and the five nucleobases that form the building blocks of RNA and DNA. In other words, the sample contains a wealth of material showing that critical ingredients for life as we know it exist on a space rock roughly the same age as Earth. The only thing missing, it would seem, were little green men.
The OSIRIS-REx mission scooped the samples from Bennu when the asteroid was about 200 million miles (322 million kilometers) from Earth. NASA successfully brought the samples to Earth’s surface and—after some difficulties—opened the canister containing the rocky bits.
The OSIRIS-REx team collected more than twice the amount of asteroid material they had initially hoped to gather (4.29 ounces, or 121.6 grams), meaning that scientists have plenty to work with as they seek to decipher the history of our solar system and the origins of life itself.
“We now know from Bennu that the raw ingredients of life were combining in really interesting and complex ways on Bennu’s parent body,” said Tim McCoy, the curator of meteorities at the Smithsonian’s National Museum of Natural History, and co-lead author on the Nature paper, in a Smithsonian release. “We have discovered that next step on a pathway to life.”
When asteroids enter Earth’s atmosphere, they undergo extreme conditions, and when they land, the space rocks are inevitably covered in Earth’s own chemical cocktail. Bennu’s samples are especially useful because the asteroid is not tainted by Earth’s chemistry, similar to the samples collected from asteroid Ryugu during the Hayabusa2 mission.
Bennu is actually a broken-off chunk of a larger asteroid that is about 4.5 billion years old—roughly the same age as our solar system. That asteroid probably contained pockets of liquid water, scientists believe, and the recent evidence of brine on Bennu seems to affirm that theory.
As the sodium-rich water on Bennu evaporated, it left behind crusty mineral residue. The water is long gone, but the briny crud—minerals rich in sodium, carbon, sulfur, phosphorus, chlorine, and fluorine—remain.
The scientists who scrutinized the samples suggest that brines like those found in the asteroid bits probably also exist on other bodies in our solar system, including Saturn’s moon Enceladus and the dwarf planet Ceres. Enceladus is an exciting venue for astrobiology—the search for extraterrestrial life—because it is thought to harbor a subsurface ocean of liquid water and has been caught spitting up other ingredients for life, including hydrogen cyanide and phosphorus.
In 2023, astrobiologists told Gizmodo just how significant the Bennu samples could be for understanding the building blocks of life and how water arrived on our primordial world. The new findings add promise and intrigue to that hype.
“This is the kind of finding you hope you’re going to make on a mission,” McCoy said. “We found something we didn’t expect, and that’s the best reward for any kind of exploration.”
The wealth of samples taken from Bennu—again, nearly double what scientists had planned for—will continue to provide valuable insights into the history of our solar system and the distribution of key ingredients for life within it. So far, the samples are delivering on the promise that made OSIRIS-REx such a compelling mission, and our understanding of the cosmos is all the better for it.
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