Molecules key to the emergence of life have been discovered in the sample of an asteroid that was collected and brought back to Earth by a NASA spacecraft.
Samples of asteroid Bennu were delivered to Earth by OSIRIS-REx in October 2023, and scientists have been studying rock and dust from the cache ever since.
In the Bennu sample, they've found chemical ingredients that, on Earth, are the building blocks of life.
The scientists also found a history of saltwater that could have acted like a 'broth' for the important compounds to interact and combine.
While the results don't show evidence for life itself, they suggest the conditions necessary for life to emerge were widespread across the early Solar System.
This, say mission scientists, increases the likelihood that life could have emerged on other planets and moons.
OSIRIS-REx in a nutshell
Asteroids are primordial leftovers from the formation of the Solar System, so studying them can tell scientists what our early Solar System was like, including how it formed and evolved.
Space rocks often fall to Earth as meteorites, but they become contaminated as they make their journey through Earth's atmosphere, land on the ground and await discovery.
Sending a spacecraft to capture a pristine sample, then, is a good way to get a more pure sample in order to better study an asteroid's chemical makeup.
That's what the OSIRIS-REx mission achieved when it gathered samples from asteroid Bennu on 20 October 2020.
The capsule containing the sample touched down in a region of the US Department of Defense’s Utah Test and Training Range near Salt Lake City on 24 October 2023.
What the samples reveal
"NASA’s OSIRIS-REx mission already is rewriting the textbook on what we understand about the beginnings of our Solar System," says Nicky Fox, associate administrator, Science Mission Directorate at NASA Headquarters in Washington.
"Asteroids provide a time capsule into Earth's history, and Bennu’s samples are pivotal in our understanding of what ingredients in our Solar System existed before life started on Earth."
Two papers revealing the results were published in the journals Nature and Nature Astronomy on 29 January 2025.
The studies reveal the discovery of amino acids, 14 of the 20 that life on Earth uses to make proteins.
Also found within the Bennu samples were all five nucleobases that life on Earth uses to store and transmit genetic instructions in DNA and RNA.
And scientists also found high abundances of ammonia, which can react with formaldehyde (also detected in the samples) to form complex molecules like amino acids.
Amino acids form proteins, which fuel nearly every biological function, the team say.
Pristine sample
While the building blocks for life been found before in space rocks, the fact the Bennu sample is so pure provides strong evidence that bodies that formed far from the Sun could have played a key role in delivering the ingredients for life throughout the Solar System.
"The clues we’re looking for are so minuscule and so easily destroyed or altered from exposure to Earth’s environment," says Danny Glavin, senior sample scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and co-lead author of the Nature Astronomy paper.
"Some of these new discoveries would not be possible without a sample-return mission, meticulous contamination-control measures and careful curation and storage of this precious material from Bennu."
An environment for life
Tim McCoy, curator of meteorites at the Smithsonian’s National Museum of Natural History in Washington, and Sara Russell, cosmic mineralogist at the Natural History Museum in London, looked to discern the sort of environment formed by these molecules.
In the Nature paper, they reveal how they identified traces of 11 minerals in the Bennu sample, formed by water containing dissolved salts evaporating, leaving behind salts as solid crystals.
Such a complete set preserving an evaporation process that could have lasted thousands of years has never been found before.
The team say some minerals found in Bennu, like trona, were discovered for the first time in extraterrestrial samples.
"These papers really go hand in hand in trying to explain how life’s ingredients actually came together to make what we see on this aqueously altered asteroid," says McCoy.
"OSIRIS-REx has been a highly successful mission," says Jason Dworkin, OSIRIS-REx project scientist at NASA Goddard and co-lead author on the Nature Astronomy paper.
"Data from OSIRIS-REx adds major brushstrokes to a picture of a solar system teeming with the potential for life.
"Why we, so far, only see life on Earth and not elsewhere, that’s the truly tantalising question."
Read the Nature paper
Read the Nature Astronomy paper
