The small black fragments of the asteroid Ryugu recovered 300 million kilometers from Earth seem insignificant, but nevertheless conceal one of the building blocks necessary for the appearance of life. Japanese scientists have indeed discovered uracil, one of the components of RNA, in a sample of 10 milligrams of these fragments, according to their study published Tuesday in Nature.
The discovery lends credence to the theory, called panspermia, that life on Earth was “seeded” from space when asteroids crashed into the planet. This theory does not however exclude that 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, building blocks necessary for the appearance of life.
The study published on Tuesday looked at another of these bricks: the bases of RNA. If the DNA, with its double helix, carries the genetic information, the RNA, made up of a single ribbon, is a messenger allowing the implementation of the instructions contained in the 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 was not the result of terrestrial contamination.
“Because the meteorites landed on the surface of the Earth, where microorganisms are ubiquitous, this makes it all the more complicated to interpret the origin of molecules of such biological importance in the meteorites,” explained to AFP one of the authors of the study, Yasuhiro Oba, associate professor at the University of Hokkaido. The study of the Ryugu samples took place in several stages, after they were immersed in hot water, like “to brew tea or coffee”, Oba said. An acid solution was then used to extract the molecules which 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 is believed to have 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. Professor Oba hopes to be able to analyze other asteroid samples in the future, such as the one that the Osiris-REx probe must bring back from the asteroid Bennu, expected on Earth this year.
Another crucial mission will be the sending from Japan in 2024 of the MMX (Martian Moons eXploration) mission, which will attempt to collect samples from Phobos, one of the moons of Mars, with a return scheduled for 2029.
The small black fragments of the asteroid Ryugu recovered 300 million kilometers from Earth seem insignificant, but nevertheless conceal one of the building blocks necessary for the appearance of life. Japanese scientists have indeed discovered uracil, one of the components of RNA, in a sample of 10 milligrams of these fragments, according to their…