Ryugu is an asteroid that sometimes passes close to Earth
JAXA
All five of the main ingredients for DNA and RNA have been found in samples from the asteroid Ryugu. This strengthens the idea that asteroids may have brought the ingredients for the first living organisms to Earth long ago.
Japan’s Hayabusa 2 spacecraft visited Ryugu in 2018, where it shot two projectiles – one small and one large – into the surface of the asteroid and collected the resulting debris. It arrived back at Earth with the samples in 2020 and researchers have been analysing these in detail ever since.
Yasuhiro Oba at Hokkaido University in Japan and his colleagues examined two samples, one from the asteroid’s surface and one comprised of subsurface materials excavated by the projectiles. In both, the team found all five primary nucleobases, which are the compounds that make up the nucleic acids DNA and RNA when combined with sugars and phosphoric acid.
This isn’t the first time that nucleobases have been found in asteroid samples: they have been seen in meteorites, too, and in samples from the asteroid Bennu. The researchers did find different abundances of the various nucleobases among the various samples, though, which hints that these compounds might be useful for tracing asteroids and meteorites back to the parent bodies that they broke off from in the distant past, as well as understanding the evolution of those parent bodies over time.
The fact that nucleobases have been found in samples of asteroids like Bennu and now Ryugu speaks to the potential importance of asteroids in the history of life on Earth. “Their detection in Ryugu strongly supports their ubiquity in the solar system,” says Oba. If asteroids all over the solar system are full of the building blocks of DNA, they could have brought those to Earth billions of years ago and helped kick-start the development of life.
It is even possible that Ryugu and other asteroids have DNA and RNA on them, not just their components. “It is very likely that more complex organic molecules like nucleic acids are formed on asteroids,” says Oba. This could make asteroids even more important for the beginnings of life on Earth.
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