Hiroshi Naraoka

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>

Abstract JAXA's Hayabusa2 sample return mission visited the volatile‐rich carbonaceous (C‐type) asteroid (162173) Ryugu with the aim of ground‐truthing remote observations, returning a pristine sample from a C‐type asteroid, and strengthening links between asteroids and the meteorite collection. Here, we have conducted a systematic study of coarse (&gt;10 μm) sulfide grains in Ryugu particles C0025‐01 and C0103‐02, the CI chondrites Orgueil and Ivuna, and the CY chondrites Y‐86029 (Stage III, heated to 500–750°C) and Y‐86720 (Stage IV, &gt;750°C), using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Sulfides are sensitive tracers of secondary alteration conditions, and we find that Ryugu and the CI chondrites share a distinct sulfide assemblage that includes the iron sulfides pyrrhotite and pentlandite, and the copper sulfide cubanite, that equilibrated during periods of low temperature (~25°C) aqueous alteration. Sulfides in the CY chondrites are compositionally distinct from Ryugu and the CI chondrites as a result of post‐hydration heating. However, the occurrence of Cu‐rich sulfides in Ryugu, the CIs, and the CYs suggests a genetic relationship between these samples.