Samples returned by JAXA’s Hayabusa-2 mission from the C-type asteroid (162173) Ryugu contain all five canonical nucleobases — purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil) — pointing to a cosmic origin for some of life’s fundamental chemistry.
Hayabusa-2 image of the asteroid Ryugu as seen from a distance of 3.7 miles. A particularly large crater is visible near the center of the image. Image credit: JAXA / University of Tokyo / Kochi University / Rikkyo University / Nagoya University / Chiba Institute of Technology / Meiji University / University of Aizu / AIST.
Nucleobases are essential components of DNA and RNA, the molecules that underpin life on Earth.
Finding them in uncontaminated extraterrestrial material allows scientists to explore how these compounds can form without biological processes, and how they may be transported across the Solar System.
Earlier analyses of samples from the asteroid Ryugu detected the nucleobase uracil. By contrast, studies of meteorites and material from the near-Earth asteroid Bennu revealed a broader diversity of nucleobases.
“To accurately assess the nucleobases in extraterrestrial materials, it is essential to analyze samples minimally altered by terrestrial processes,” said Dr. Toshiki Koga from Japan Agency for Marine-Earth Science and Technology and colleagues.
“In this context, pristine asteroid samples — those not exposed to Earth’s atmosphere — hold high scientific value.”
A carbonate-rich grain in the sample of material from the near-Earth asteroid Ryugu. Image credit: Pilorget et al., doi: 10.1038/s41550-021-01549-z.
In the new study, the authors analyzed two Ryugu samples collected by the Hayabusa-2 mission.
They detected all five canonical nucleobases — adenine, guanine, cytosine, thymine, and uracil — in both samples.
They compared the results with those obtained from the Murchison and Orgueil meteorites and with the returned samples from the asteroid Bennu.
They found significant differences in the relative abundances of the nucleobases.
More specifically, Ryugu contains roughly comparable amounts of purine and pyrimidine nucleobases, while Murchison has more purine nucleobases while samples from Bennu and Orgeuil are richer in pyrimidine nucleobases.
These results reflect the different chemical, environmental, and evolutionary histories of their respective parent bodies.
The detection of these nucleobases in asteroid and meteorite materials, despite their chemical differences, implies that they are widespread throughout the Solar System.
The findings also suggest that carbonaceous asteroids may have contributed to the chemical inventory of the early Earth.
“An analysis of pristine nucleobase distributions and their isotopic compositions in other carbonaceous meteorites would offer critical insights into the origins of these compounds and the astrochemical processes involving nitrogen-containing molecules,” the researchers said.
“The universal detection of all five canonical nucleobases in samples from the carbonaceous asteroids Ryugu and Bennu highlights the potential contribution of these exogenous molecules to the organic inventory that supported prebiotic molecular evolution and ultimately enabled the emergence of RNA and DNA on the early Earth.”
The study appears this week in the journal Nature Astronomy.
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T. Koga et al. A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu. Nat Astron, published online March 16, 2026; doi: 10.1038/s41550-026-02791-z
