Scientists have discovered that a sample of the Ryugu asteroid collected by the Japanese spacecraft Hayabusa 2 contains the nucleobases adenine, guanine, cytosine, thymine and uracil, the building blocks of DNA and RNA on which all life is based.
Because asteroids like Ryugu formed 4.6 billion years ago when the planets were born around the infant sun, and have remained relatively untouched since then, the discovery sheds new light on the chemical conditions that existed at the dawn of the solar system.
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The Japan Aerospace Exploration Agency (JAXA) Hayabusa 2 mission collected samples from asteroid Ryugu between 2018 and 2019. The spacecraft returned these samples to Earth on December 5, 2020.
Carbonaceous asteroids like the spinneret-shaped Ryugu contain what is effectively a “fossil record” of pristine material from the earliest era of the solar system, which is why scientists are so keen to get them back here to Earth for close-up study.
The study of the two samples returned to Earth has previously shown that Ryugu once had liquid water flowing over the surface, strengthening the theory that these space rocks may have supplied water to the surface of our planet.
This team, led by JAXA biogeochemist Toshiki Koga, analyzed two Ryugu samples returned by Hayabusa 2, and found adenine, guanine, cytosine, thymine and uracil. The results were compared with findings obtained when researchers studied samples returned from the asteroid Bennu, and with examinations of the Murchison and Orgueil meteorites, collected from Australia in 1969 and France in 1864, respectively. The team discovered significant differences in the concentration of nucleobases.
Ryugu contains roughly comparable amounts of the nucleobases, adenine and guanine (known as purines), with cytosine, thymine and uracil (pyrimidines). However, Murchison is richer in purine nucleobases, while Orgeuil samples from Bennu are richer in pyrimidine nucleobases.
These differences may reflect the different evolutionary histories and environmental birthplaces of Ryugu, Bennu, and the parents of the Murchison and Orgeuil samples. The research further emphasizes the role that asteroids likely played in building the chemical diversity that allowed life to arise on Earth.
Perhaps the most important result of this study is the implication that the building blocks of DNA and RNA are widely dispersed throughout the solar system.
The team’s research was published in the journal Natural astronomy.
