Uracil, a building block of life, was found on the asteroid Ryugu.
Yasuhiro Oba and his colleagues discovered the precursor to life in samples taken from the asteroid and returned to Earth by the Japanese spacecraft Hayabusa2, the team reports March 21 to Nature Communication.
“The detection of uracil in the Ryugu sample is very important to clearly demonstrate that it is actually present in extraterrestrial environments,” says Oba, an astrochemist at Hokkaido University in Sapporo, Japan.
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Uracil had previously been detected in samples of meteorites, including a rare class called CI-chondrites, which are abundant in organic compounds. But these meteorites landed on Earth, leaving open the possibility that they were contaminated by humans or the Earth’s atmosphere. Because the Ryugu samples were collected in space, they are the the purest elements of the solar system that scientists have studied to date (SN: 09/06/22). This means the team could rule out the influence of terrestrial biology.
Oba’s team received only about 10 milligrams of Ryugu’s sample for analysis. As a result, the researchers weren’t confident they would be able to detect building blocks, even if they had previously been able to. detect uracil and other nucleobases in meteorites (SN: 4/26/22).
Nucleobases are biological building blocks that form the structure of RNA, which is essential for the creation of proteins in all living cells. A theory of the origin of life suggests that RNA preceded DNA and proteins and that ancient organisms relied on RNA for the chemical reactions associated with life (SN: 04/04/04).
The team used hot water to extract organic matter from the Ryugu samples, then acid to further break the chemical bonds and separate the uracil and other smaller molecules.
Laura Rodriguez, a prebiotic chemist at the Lunar and Planetary Institute in Houston, Texas, who was not involved in the study, says this method leaves open the possibility that uracil was separated from a longer chain of molecules in course of the process. “I think it would be interesting in future work to look at more complex molecules rather than just nucleobases,” Rodriguez says.
She says she has seen in her research that nucleobases can form bonds to create more complex structures, such as a possible nucleic acid precursor that can lead to the formation of RNA. “My question is, do these more complex structures also form in asteroids? »
Oba says his team plans to analyze samples from NASA’s OSIRIS-REX mission, which caught a bit of asteroid Bennu in 2020 and will send him back to Earth this fall (SN: 10/21/20).