Life on Earth may have origins from far, far away. Scientists have found a full set of life-building molecules in a nearly pristine asteroid sample, and the discovery suggests that the necessary ingredients to kick-start the evolution of life on Earth may have come from a celestial-body delivery. It also raises questions as to whether more complex molecules are present all over the solar system.
Back to basics
Asteroid Ryugu has all five of the primary nucleobases, according to a study published in the journal Nature Astronomy. The nucleobases — adenine, thymine, guanine, cytosine and uracil — are “compounds that make up the nucleic acids DNA and RNA when combined with sugars and phosphoric acid,” said New Scientist. They are the building blocks of the genetic code, and life as we know it could not exist without them. The bases are split into two categories: purines (adenine and guanine) and pyrimidines (thymine, cytosine and uracil).
Samples of asteroid Ryugu were collected by the Japanese Aerospace Agency’s (JAXA) Hayabusa2 mission. The samples were brought to Earth in December 2020. Asteroids like Ryugu “formed 4.6 billion years ago when the planets were being born around the infant sun,” said Space.com (a sister site of The Week). Since then, they have “remained relatively unspoiled.” Finding these nucleobases on the asteroid “hints that they can be formed without the presence of life and may offer clues into how these compounds could be transported across the solar system.”
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Ryugu is not the only asteroid with nucleobases. They were also found in samples from asteroid Bennu, which were brought to Earth in 2023, as well as in the Murchison meteorite collected from Australia in 1969 and the Orgueil meteorite collected from France in 1864.
However, the “precise mixture of molecules” varied “depending on the asteroid’s chemical environment and history,” Kliti Grice, a professor of organic and isotope geochemistry at Curtin University, said at The Conversation. Ryugu contained roughly equal amounts of purines and pyrimidines, while Murchison was richer in purine nucleobases. Orgeuil and Bennu were richer in pyrimidine nucleobases. Ammonia may be the reason for the different balances, as “samples from Ryugu, Bennu and the Orgueil meteorite that contained more ammonia all tended to have a lower ratio of purines to pyrimidines,” said Gizmodo.
Obscure origins
Discovering these components in these otherworldly sources gives more insight as to how life developed on Earth. The nucleobases in all four of the samples “suggest key components of genetic material may have formed in space and later delivered to the early Earth,” said Grice. The “story of life on our planet may be deeply connected to the chemistry of such ancient asteroids.”
Much is still unknown about these compounds’ origins. “Ammonia may have played an important role in shaping the composition of nucleobases in these materials,” Toshiki Koga, a postdoctoral researcher at the Japan Agency for Marine-Earth Science and Technology and study co-author, said to Gizmodo. “Because no known formation mechanism predicts such a correlation, it may indicate that previously unrecognized chemical pathways contributed to the formation of nucleobases in the early solar system.”
The detection of the bases in Ryugu also “strongly supports their ubiquity in the solar system,” Yasuhiro Oba, an astrophysical chemist at Hokkaido University in Japan and study co-author, said to New Scientist. Other asteroids may contain actual strands of DNA and RNA and not just the components. “It is very likely that more complex organic molecules like nucleic acids are formed on asteroids.”
