All 5 genetic letters of DNA and RNA discovered in 4.5B-year-old asteroid

Researchers have detected all five canonical nucleobases - the molecular units used in DNA and RNA - in samples from asteroid Ryugu. Japan’s Hayabusa2 mission returned 5.4 grams of the asteroid’s material to Earth in 2020, and a Japanese team analyzed two samples under ultra-clean conditions to limit contamination. They extracted and purified organic molecules, finding adenine, guanine, cytosine, thymine and uracil in roughly similar amounts. Uracil had been reported in Ryugu samples earlier; the new analysis completes the set. Nucleobases combine with sugars and phosphates to form nucleotides, the building blocks of genetic material.

The finding adds to evidence that prebiotic organic chemistry was widespread in the early Solar System. All five bases have also been identified in samples from asteroid Bennu, while carbon-rich meteorites such as Murchison and Orgueil contain varied organic molecules, though rocks that fell to Earth may be contaminated. Comparisons show asteroid chemistry differs: Murchison is richer in purines, while Bennu and Orgueil have more pyrimidines, a balance that may depend on conditions such as ammonia abundance. Ryugu’s protected samples preserve a particularly clear record of ancient chemistry. The results support the possibility that asteroids formed life’s molecular ingredients and delivered some to early Earth, but they do not show that life itself existed in space or explain how life began.