Scientists analyzing samples from the asteroid Bennu have identified the full set of nucleobases—key molecular components of DNA and RNA—alongside an array of life-essential minerals. This marks the first time all five nucleobases have been detected on an extraterrestrial body, reinforcing the idea that the fundamental building blocks of life may have formed beyond Earth.
The findings come from an extensive analysis of material collected by NASA’s OSIRIS-REx spacecraft, which successfully returned a sample from Bennu to Earth in October 2023. Two independent research teams, publishing their results in Nature Astronomy, found that this space rock contains a wealth of chemical compounds linked to the early formation of life on our planet.
A Celestial Time Capsule: Bennu’s 4.6-Billion-Year-Old Chemistry
Bennu, a carbon-rich asteroid, is a relic from the birth of the solar system, making it a valuable time capsule for scientists studying the origins of organic molecules. The sample’s composition reveals an abundance of carbon, sulfur, phosphorus, fluorine, and sodium—elements commonly associated with biological activity on Earth. Some minerals discovered on Bennu closely resemble those found in dried lake beds on our planet, yet they predate Earth’s earliest oceans by billions of years.
“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, a curator at the Smithsonian’s National Museum of Natural History and co-author of one of the studies.
A Cosmic Recipe for Life?
One of the most intriguing aspects of this discovery is the presence of sodium carbonate—a mineral typically found in evaporated lakes that once supported microbial life on Earth. Within these carbonate deposits, researchers identified 11 key minerals known to serve as precursors to organic compounds. These formations suggest that Bennu may have once harbored liquid water, a crucial ingredient for life.
A separate team of Japanese scientists further analyzed a different portion of the sample and confirmed the presence of all five nucleobases: adenine, guanine, cytosine, thymine, and uracil. These molecules, when combined with ribose and phosphate, form the backbone of DNA and RNA, the genetic code of all living organisms.
The discovery builds upon previous research from Japan’s Hayabusa2 mission, which retrieved a sample from asteroid Ryugu in 2023. While Ryugu contained uracil, it lacked the full set of nucleobases, making Bennu the first extraterrestrial body confirmed to contain all five.
Did Bennu Support the Origins of Life?
While the presence of life-essential molecules on Bennu is undeniable, whether these compounds had the right conditions to evolve into complex biological structures remains uncertain. Scientists speculate that similar briny environments may exist elsewhere in the solar system, including on Ceres and Saturn’s moon Enceladus, raising the possibility that life-friendly chemistry is more widespread than previously thought.
To explore this further, researchers plan to reexamine meteorites in their collection, searching for traces of the same minerals and organic molecules found on Bennu. If they discover similar compounds in other space rocks, it could support the hypothesis that life’s essential ingredients are not unique to Earth but rather part of a broader cosmic phenomenon.
Beyond Science: The Risk Factor of Bennu
Aside from its potential role in understanding life’s origins, Bennu has drawn attention for another reason—it is considered one of the most hazardous asteroids known to scientists. With a 1-in-2,700 chance of striking Earth in the year 2182, Bennu’s trajectory is closely monitored by space agencies. Understanding its composition and structure is critical not just for planetary defense but also for future asteroid resource exploration.
NASA’s OSIRIS-REx mission, which launched in 2016, spent two years orbiting Bennu before collecting its sample using an innovative nitrogen burst system designed to avoid surface contamination. After a seven-year journey covering 320 million kilometers (200 million miles), the spacecraft successfully delivered its cargo to Earth, where scientists are now unlocking its secrets.
Bennu’s sample provides compelling evidence that the chemical precursors to life may have originated in space and could have been delivered to Earth via asteroids. This groundbreaking research not only deepens our understanding of early planetary chemistry but also opens new doors in the search for life beyond our world.
