All five of the nucleobases that carry genetic information in DNA and RNA have been found in samples returned from the asteroid Ryugu, a team of Japanese scientists has reported in Nature Astronomy.
The finding was written up for a general readership by The Conversation, in an article republished by ScienceDaily. An international team had reported one of the five, uracil, in the same material in 2023.
Nucleobases are nitrogen-containing organic molecules. The five are adenine and guanine, known as purines, and cytosine, thymine and uracil, known as pyrimidines. Combined with sugars and phosphates they yield nucleotides, the building blocks of genetic material. Without nucleobases, the genetic code that allows organisms to grow, reproduce and evolve would not exist.
The samples were collected in space and brought to Earth in 2020 by the Japan Aerospace Exploration Agency's Hayabusa2 mission, which delivered 5.4 grams of pristine asteroid material in total. Researchers handle it in ultra-clean laboratory conditions to avoid contaminating it.
The team extracted organic molecules using water and hydrochloric acid, purified them for detection, and found all five nucleobases in the two Ryugu samples they analysed, in roughly similar amounts.
The result is consistent with earlier work on space rocks. The Murchison meteorite, which fell in Australia in 1969, and the Orgueil meteorite, which fell in France in 1864, have both yielded a rich variety of organic molecules including nucleobases, although meteorites that land on Earth can be contaminated by the journey and the landing. Pristine samples from NASA's mission to the asteroid Bennu also yielded all five in 2025.
Asteroids such as Ryugu and Bennu, and the parent body of the Orgueil meteorite, are remnants of the early Solar System and can preserve material largely unchanged for about 4.5 billion years. Their chemistry differs: Murchison is enriched in purines, while Bennu and Orgueil contain more pyrimidines, a balance thought to be influenced by ammonia.
Because the Ryugu material was collected directly in space and protected from terrestrial contamination, it offers one of the clearest available views of ancient Solar System chemistry, and suggests the molecular ingredients of life were already forming in space billions of years ago and may later have been delivered to the early Earth.
It is worth being precise about what has been established. Ryugu holds the complete set of letters used to write every genome on this planet, in roughly similar amounts, and has held them for about four and a half billion years.
In that time it has written nothing. This newspaper considers the omission the most striking result in the paper. The alphabet, it turns out, was never the bottleneck.
The comparison with Murchison and Orgueil sharpens the point rather than softening it. Those bodies are short of purines or short of pyrimidines and have equally little to show for themselves. Ryugu is the first object confirmed to have had every excuse removed and to have continued, without interruption, as a rock.
Our analysts have reviewed the chemistry and accept that arrangement, rather than inventory, is the difficulty. The Department of Unnecessary Research has nonetheless written to the authors to confirm the one point the paper leaves implicit: that a body in possession of the entire genetic alphabet, for four and a half billion years, has produced no sequence of any length, and is therefore the longest documented case of writer's block.