The small black fragments from the asteroid Ryugu, recovered 300 million kilometers from Earth, appear insignificant, but they still hide one of the building blocks necessary for life to arise. Japanese scientists have indeed detected uracil, one of the components of RNA, in a 10 milligram sample of these fragments, according to their study published in Nature on Tuesday.
The discovery lends credence to the theory, dubbed panspermia, that life on Earth was “seeded” from space when asteroids impacted the planet. However, this theory does not rule out the appearance of life on Earth from the primordial oceans or even their 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.
Hayabusa-2 was launched from Earth in 2014 and returned to Earth orbit in 2020 to release a capsule containing the sample. The latter, divided among several international research teams, has already yielded discoveries such as the presence of amino acids, building blocks necessary for the emergence of life.
The study, published on Tuesday, looked at another of these building blocks: the bases of RNA. When the DNA, with its double helix, carries the genetic information, the single-stranded RNA is a messenger that enables the instructions contained in the DNA to be carried out.
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 sure that this presence was not the result of terrestrial contamination.
“Because the meteorites landed on the Earth’s surface, where microorganisms are ubiquitous, it is all the more complicated to interpret the origin of molecules of such biological importance in the meteorites,” one of the study’s authors told AFP. Yasuhiro Oba, Associate Professor at the University of Hokkaido. Examination of the Ryugu samples took place in several stages, after they were immersed in hot water, like “for brewing tea or coffee,” Oba said. An acid solution was then used to extract the molecules, which were analyzed with highly sensitive instruments to identify uracil. The discovery provides “strong evidence that one of the components of RNA was brought to Earth before life arose” via a Ryugu-like asteroid thought to have crashed onto our planet, according to Oba. Who “assumes” that such a deposit “played a role in prebiotic evolution and possibly the origin 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 in too small amounts to be detectable. Professor Oba hopes to be able to analyze more asteroid samples in the future, such as the one the Osiris-REx probe must bring back from asteroid Bennu, which is expected to return to Earth this year.
Another crucial mission will be the deployment of the MMX (Martian Moons eXploration) mission from Japan in 2024, which will attempt to collect samples from Phobos, one of Mars’ moons, with a return planned for 2029.
The small black fragments from the asteroid Ryugu, recovered 300 million kilometers from Earth, appear insignificant, but they still hide one of the building blocks necessary for life to arise. In fact, Japanese scientists discovered uracil, one of the components of RNA, in a 10 milligram sample of these fragments.