How life began on Earth remains one of science’s biggest mysteries, but many researchers agree on one major idea: life likely emerged through chemical evolution, where simple chemicals gradually formed more complex molecules over time. Another closely related theory suggests that asteroids and comets may have helped kick-start that process by delivering organic molecules to early Earth. If true, it would mean some of the key building blocks of genetics can form naturally in space—and arrive here ready to participate in life-forming chemistry.
A strong candidate for that cosmic delivery system is the asteroid 162173 Ryugu. Ryugu is known as a carbonaceous asteroid, meaning it is rich in carbon and contains water-bearing minerals along with diverse organic compounds. Scientists describe it as a primitive object—essentially a time capsule from the early solar system. Its unusual spinning-top shape has also drawn attention, and researchers think it may have formed from the debris of a much larger asteroid that broke apart long ago.
To find out what Ryugu is really made of, Japan launched the Hayabusa2 mission in 2014. The spacecraft travelled to Ryugu, collected material directly from the asteroid, and successfully returned those samples to Earth for detailed laboratory analysis. Earlier work on the samples revealed the presence of uracil, one of the nucleobases used in RNA—an exciting result because nucleobases are central components of genetic material.
Now, a newer study has taken the investigation further by searching for all of the nucleobases used in DNA and RNA within the Ryugu samples. Finding a broader set of these genetic building blocks strengthens the case that the chemistry needed for life’s foundational molecules can occur beyond Earth.
What makes the results even more compelling is that similar nucleobase findings have also been reported from another well-studied asteroid, 101955 Bennu. Seeing comparable chemical ingredients across multiple asteroids suggests these molecules may not be rare anomalies. Instead, they could be relatively common in carbon-rich bodies throughout the solar system—raising the possibility that early Earth may have received repeated deliveries of life-relevant organic material over long periods of time.
Researchers also identified ammonia in the Ryugu sample analysis, adding another important piece to the puzzle. Ammonia is a key nitrogen-bearing compound that can participate in chemical reactions leading to amino acids and other biomolecules. Its presence supports the broader idea that asteroids can carry a surprisingly rich chemistry, including ingredients strongly associated with prebiotic processes.
It’s important to be clear about what this discovery does—and does not—mean. The presence of DNA and RNA nucleobases in asteroid samples is not evidence that life began in space. Rather, it supports a more subtle but powerful conclusion: the ingredients for life can form in space naturally, and asteroids may have helped deliver those ingredients to Earth, potentially giving chemical evolution a valuable head start.
