Astrobiology / Cosmochemistry
A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu
Scientists have confirmed all five DNA/RNA nucleobases in pristine asteroid Ryugu samples, strengthening the case that carbonaceous asteroids seeded early Earth with the building blocks of life.
Imagine DNA as a message written in a 4-letter alphabet. Those 'letters' are called nucleobases, and there are five of them: A, T, G, C, and U. Scientists collected tiny rock samples from an asteroid called Ryugu — a rock floating in space about 300 million kilometers from Earth — using a robotic spacecraft. When they looked very carefully at those rocks in a laboratory, they found ALL five of those biological 'letters' inside. Nobody put them there; they formed naturally in space through chemistry involving ice, water, and simple ingredients like ammonia. It's like finding all the pieces of an alphabet scattered across the cosmos, ready to be assembled into the language of life.
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All five canonical nucleobases (adenine, guanine, cytosine, thymine, and uracil) were detected in samples returned from asteroid Ryugu by JAXA's Hayabusa2 mission.
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Ryugu samples contain nearly equal amounts of purines and pyrimidines, in contrast to Murchison (enriched in purines) and Bennu/Orgueil (enriched in pyrimidines).
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Purine-to-pyrimidine ratios in Ryugu, Bennu, and Orgueil negatively correlate with ammonia content, suggesting a shared nucleobase formation pathway dependent on parent body physicochemical environment.
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The findings demonstrate the widespread presence of nucleobases throughout the Solar System and support the hypothesis that carbonaceous asteroids delivered prebiotic molecules to early Earth.
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Pristine asteroid samples from Hayabusa2 provide unambiguous evidence of abiotic nucleobase synthesis under interstellar ice and aqueous planetary conditions.
Organic molecules delivered from extraterrestrial materials may have played a key role in supplying building blocks for life on Earth. Here we report all five canonical nucleobases—purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil)—in samples returned from the C-type asteroid (162173) Ryugu by JAXA’s Hayabusa2 mission and compare the results with data from similar extraterrestrial material. Ryugu samples contain nearly equal amounts of purines and pyrimidines, whereas Murchison is enriched in purines and Bennu and Orgueil in pyrimidines. Samples from Ryugu, Bennu and Orgueil, which have a similar mineralogy and elemental composition, show purine-to-pyrimidine ratios negatively correlating with ammonia. These observations indicate that the nucleobases in these samples may have formed via a shared pathway depending on the physicochemical environment of the respective parent bodies. The detection of diverse nucleobases in asteroid and meteorite materials demonstrates their widespread presence throughout the Solar System and reinforces the hypothesis that carbonaceous asteroids contributed to the prebiotic chemical inventory of early Earth.