A new study reveals all five fundamental nucleobases – the molecular “letters” of life – have been detected in samples from the asteroid Ryugu. Asteroid particles offer a glimpse into the chemical ingredients that may have helped kindle life on Earth. The Ryugu samples were returned from space in 2020 by Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 mission.
In 2023, an international team reported they had found one of the nucleobases in these samples – uracil. Now, in a study published in Nature Astronomy, a team of Japanese scientists has confirmed all five nucleobases are present in this pristine asteroid material. This means these ingredients for life may have been widespread throughout the Solar System in its early years.
Nucleobases are nitrogen-containing organic molecules that form the “letters” of genetic information in DNA and RNA. The five main nucleobases are adenine and guanine (known as purines), as well as cytosine, thymine and uracil (known as pyrimidines). These molecules combine with sugars and phosphates to yield nucleotides – the building blocks of genetic material.
Without nucleobases, the genetic code that allows organisms to grow, reproduce and evolve would not exist. By studying purines and pyrimidines in Ryugu samples, scientists can reconstruct the chemical history of primitive asteroids. In turn, this gives us a better understanding of how the building blocks of life may have been formed and existed across the Solar System.
Hayabusa2 delivered a total of 5.4 grams of pristine asteroid material. Researchers have to use ultra-clean lab conditions to avoid contaminating it. They extracted organic molecules using water and hydrocholoric acid, and then purified them for further detection.
They found all five nucleobases in the two Ryugu samples they analysed, in roughly similar amounts. The new results align with previous findings on space rocks. The Murchison meteorite that fell in Australia in 1969, and the Orgueil meteorite in France, 1864, have previously yielded a rich variety of organic molecules, including nucleobases.
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