Scientists have spent decades debating whether the chemical ingredients for life could have arrived on Earth from space. A new finding from one of the most closely studied asteroid samples ever collected moves that conversation forward.
Researchers analyzing material retrieved from the asteroid Ryugu have confirmed the presence of all five nucleobases — adenine, guanine, cytosine, thymine, and uracil — the molecular building blocks that form the genetic code of DNA and RNA. According to the report, this marks the first time all five have been identified together in a single asteroid sample.
The team was led by JAXA biogeochemist Toshiki Koga. They examined two samples returned to Earth by Japan Aerospace Exploration Agency‘s Hayabusa 2 spacecraft, which collected material from Ryugu between 2018 and 2019 before delivering it to Earth on Dec. 5, 2020.
What the Nucleobase Ratios Reveal
The detection alone is significant. But the study goes further, comparing Ryugu‘s nucleobase composition against samples from the asteroid Bennu and two meteorites — the Murchison meteorite, collected in Australia in 1969, and the Orgueil meteorite, recovered in France in 1864.
The differences are notable. Ryugu contains roughly balanced amounts of purine nucleobases (adenine and guanine) and pyrimidine nucleobases (cytosine, thymine, and uracil). The Murchison meteorite is richer in purines. Samples tied to Orgueil and Bennu, by contrast, skew toward pyrimidines. The study states these disparities likely reflect distinct evolutionary histories and environmental formation conditions for each body.
Because Ryugu is a carbonaceous asteroid — formed approximately 4.6 billion years ago alongside the planets — it holds relatively unspoiled material from the solar system’s earliest period. Previous analysis of the same samples had already shown evidence that liquid water once existed on the asteroid’s surface, a detail that reinforced theories about space rocks delivering water to early Earth.
Life’s Ingredients Without Life
The presence of nucleobases in asteroid material carries a specific implication: these molecules can form in the absence of living organisms. The finding supports the idea that the chemical diversity needed for life to emerge on Earth may have been seeded, at least in part, by asteroid impacts over billions of years.
It also points to something broader. If nucleobases exist in Ryugu, in Bennu, and in meteorites that fell to Earth over a century apart, the building blocks of genetic material appear to be widely distributed across the solar system — not a rare accident confined to one planet.
The research was published in the journal Nature Astronomy.
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