Japanese scientists have discovered uracil, one of the components of RNA, in a 10-milligram sample of these fragments, according to their study published Tuesday in Nature.

This discovery is grist to the mill of the theory, called panspermia, that life on Earth was "seeded" from space when asteroids crashed into the planet. This theory does not exclude the theory of the appearance of life on Earth from the primitive oceans, or even its atmosphere.

The study published in Nature is the latest to examine the 5.4 grams of fragments and dust recovered by the Japanese probe Hayabusa-2 on the asteroid Ryugu.

Launched from Earth in 2014, Hayabusa-2 returned to Earth orbit in 2020 to release a capsule containing the sample. The latter, divided between several international teams of researchers, has already delivered discoveries, such as the presence of amino acids, the building blocks necessary for the appearance of life.

The study published Tuesday looked at another of these bricks: the basics of RNA. If DNA, with its double helix, carries genetic information, RNA, consisting of a single ribbon, is a messenger allowing the implementation of the instructions contained in DNA.

A component "delivered" to Earth

RNA consists of four bases: adenine, guanine, cytosine and uracil. Scientists had found them in meteorites, fragments of asteroids, but could not be certain that this presence did not result from terrestrial contamination.

Asteroid Ryugu in a photo released on November 13, 2019 by the Japanese Space Agency (JAXA) © Handout / JAXA via Jiji Press / AFP / Archives

"As meteorites have landed on the Earth's surface, where microorganisms are ubiquitous, this makes it all the more complicated to interpret the origin of molecules of such biological importance in meteorites," Yasuhiro Oba, an associate professor at Hokkaido University, told AFP.

The study of Ryugu's samples took place in several stages, after they were immersed in hot water, as "to brew tea or coffee," Oba said. An acidic solution was then used to extract the molecules that were analyzed using ultra-sensitive instruments, and to identify uracil.

The discovery offers "strong evidence that one of the components of RNA was delivered to Earth even before life emerged," via a Ryugu-like asteroid that crashed into our planet, according to Oba. Who "assumes" that such a deposit "played a role in prebiotic evolution and possibly the appearance of life" on Earth.

The other RNA components were not identified in the Ryugu samples, although the researcher does not rule out their presence but at levels too low to be detectable.

Oba hopes to be able to analyze other asteroid samples in the future, such as the one that the Osiris-REx probe is expected to bring back from asteroid Bennu, expected on Earth this year.

Another crucial mission will be the sending from Japan in 2024 of the MMX mission (Martian Moons eXploration), which will attempt to collect samples from Phobos, one of Mars' moons, with a return scheduled for 2029.

© 2023 AFP