All key components that make up the genetic material of Earth's life forms have been identified in samples directly brought from the asteroid Ryugu by the Japanese probe Hayabusa2. The findings are expected to provide important clues to how the ingredients for life were formed and transported in the early solar system.
A research team led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) said it detected all five nucleobases that constitute deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) of Earth's life in samples from the asteroid Ryugu. The results were published in the international journal Nature Astronomy on the 17th.
Nucleobases are the basic components that make up DNA and RNA, which serve as the blueprint for life. If DNA and RNA are sentences, nucleobases are akin to the letters that compose those sentences. Scientists have long tracked whether nucleobases can form in space without life, and how they spread throughout the solar system.
The team analyzed two samples collected from Ryugu and confirmed that adenine (A), guanine (G), cytosine (C), and thymine (T), which constitute DNA, and uracil (U), which is found in RNA, were all present. Although uracil had been found in Ryugu in prior research, this time the full set of nucleobases was identified.
What makes this study particularly noteworthy is that the Ryugu samples are space materials recovered in a state with a very low possibility of contamination by Earth's environment.
Park Yunsu, senior researcher at the Galaxy Evolution Research Center of the Korea Astronomy and Space Science Institute (KASI), said, "Nucleobases have been found in carbonaceous meteorites, but many meteorites were stored for long periods after exposure to Earth's atmosphere, water, and microorganisms, making it difficult to completely rule out contamination by Earth's environment," adding, "It is significant that all five nucleobases were confirmed in asteroid Ryugu samples directly collected without exposure to Earth's environment."
The team also compared the results with the Murchison and Orgueil meteorites that fell to Earth, as well as samples of the asteroid Bennu brought back by a U.S. probe. They found a commonality in the presence of nucleobases, but the types that were more abundant differed markedly by celestial body.
Nucleobases are broadly divided into the purine family, including adenine and guanine, and the pyrimidine family of cytosine, thymine, and uracil. On Ryugu, purines and pyrimidines existed at similar levels, but the Murchison meteorite had more purines. The Bennu and Orgueil samples were richer in pyrimidines.
The researchers concluded that because each asteroid formed and evolved under different conditions, the types and amounts of nucleobases they contain also diverged. In other words, depending on which substances were present and how much they were exposed to water and heat, the types and ratios of nucleobases formed could vary.
However, the team did not interpret this as a trace of life. That is because, along with thymine used in the DNA of life, they also detected 6-methyluracil, which has a similar structure but is rarely used by living organisms. This suggests that Ryugu's nucleobases were not produced by organisms but may have formed through natural chemical reactions within the asteroid.
The team also explained that the study lends weight to the possibility that carbon-rich asteroids supplied the building blocks of life to early Earth. While it cannot be concluded that life itself came from space, the likelihood has increased that organic molecules necessary for life's emergence, such as nucleobases, were naturally produced in space and transported via asteroids or meteorites.
Park Changgeun, principal researcher at the Glaciology Research Division of the Korea Polar Research Institute (KOPRI), said, "Ryugu and Bennu samples are very similar in overall chemical composition, but when examined in detail, they are by no means homogeneous in parts. Therefore, in studies analyzing extremely small amounts of sample, there can be debate about how representative the results are of the entire asteroid," while adding, "I expect such studies will gradually help answer the fundamental question of whether the materials underpinning Earth's life came from outside Earth or formed within it."
References
Nature Astronomy (2026), DOI: https://doi.org/10.1038/s41550-026-02791-z