奈良岡 浩

Abstract <p>Organic molecules delivered from extraterrestrial materials may have played a key role in supplying building blocks for life on Earth. Here we report the detection of all five canonical nucleobases—adenine, guanine, cytosine, thymine, and uracil—in samples returned from the C-type asteroid (162173) Ryugu by JAXA’s Hayabusa2 mission. The definitive identification of a complete set of nucleobases in carbonaceous asteroid samples—following detection in Bennu—strongly suggests that these essential components of DNA and RNA are widespread throughout the Solar System. Comparative analysis with Bennu and the Orgueil meteorite shows purine and pyrimidine abundances vary and correlate with ammonia concentrations, linking to physicochemical environments of their parent bodies and providing new insights into extraterrestrial nucleobase formation pathways. The identification of diverse nucleobases in asteroidal and meteoritic materials reinforces the hypothesis that carbonaceous asteroids contributed to the prebiotic chemical inventory of early Earth.</p>