All 5 fundamental units of life's genetic code were just discovered in an asteroid sample
by Kliti Grice, The Conversation
edited by Gaby Clark, reviewed by Robert Egan
Discovery Overview
A new study reveals all five fundamental nucleobases—the molecular "letters" of life—have been detected in samples from the asteroid Ryugu.
Asteroid particles offer a glimpse into the chemical ingredients that may have helped kindle life on Earth. The Ryugu samples were returned from space in 2020 by Japan Aerospace Exploration Agency's (JAXA) Hayabusa2 mission.
In 2023, an international team reported they had found one of the nucleobases in these samples—uracil. Now, in a study published in Nature Astronomy today, a team of Japanese scientists has confirmed all five nucleobases are present in this pristine asteroid material.
Importance of Nucleobases
Nucleobases are nitrogen-containing organic molecules that form the "letters" of genetic information in DNA and RNA. The five main nucleobases are adenine and guanine (known as purines), as well as cytosine, thymine and uracil (known as pyrimidines).
These molecules combine with sugars and phosphates to yield nucleotides—the building blocks of genetic material. Without nucleobases, the genetic code that allows organisms to grow, reproduce and evolve would not exist.
By studying purines and pyrimidines in Ryugu samples, scientists can reconstruct the chemical history of primitive asteroids, thus gaining insights into how life's building blocks may have formed and existed across the solar system.
Significance of the Findings
Hayabusa2 delivered a total of 5.4 grams of pristine asteroid material. Researchers have to use ultra-clean lab conditions to avoid contaminating it. They extracted organic molecules using water and hydrochloric acid, and then purified them for further detection.
They found all five nucleobases in the two Ryugu samples they analyzed, in roughly similar amounts.
Comparison with Previous Findings
The new results align with previous findings on space rocks. The Murchison meteorite that fell in Australia in 1969, and the Orgueil meteorite in France, 1864, have previously yielded a rich variety of organic molecules, including nucleobases.
Of course, meteorites that land on Earth can be contaminated by their journey and landing. But pristine samples from NASA's mission to asteroid Bennu also yielded all five nucleobases in 2025.
Asteroids such as Ryugu and Bennu are remnants of the early solar system. They can preserve materials largely unchanged for about 4.5 billion years.
Interestingly, these asteroids show chemical differences. Murchison is enriched in purines, while Bennu and Orgueil contain more pyrimidines. It is believed this balance may be influenced by ammonia, a key molecule that can shape which nucleobases can form.
By examining Ryugu's samples and comparing them with meteorites like Murchison and Orgueil, researchers are tracing the cosmic journey of life's probable molecular ingredients.
Conclusion
The discoveries suggest that carbon-rich asteroids throughout the solar system may contain diverse prebiotic chemistry capable of supporting life. The precise mixture of molecules, such as between purines and pyrimidines, varies depending on the asteroid's chemical environment and history.
The comprehensive analysis of Ryugu samples reinforces the notion that some molecular ingredients necessary for life may have formed in space and were potentially transferred to early Earth, thereby intertwining the origin of life with the broader cosmic chemical history.
Acknowledgments and References
Toshiki Koga et al, A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu, Nature Astronomy (2026). DOI: 10.1038/s41550-026-02791-z
Journal information: Nature Astronomy
Key concepts
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