Scientists find the five building blocks of life on the asteroid Ryugu

BarcelonaAdenine, guanine, cytosine, thymine, and uracil are the five basic organic building blocks of life on Earth. They are considered the bricks of the genetic code, because the order in which they appear within DNA and RNA determines how genetic information is created, stored, and transmitted, and therefore how any living organism, including humans, functions. But their origin remains a mystery. One of the major scientific hypotheses is that these basic building blocks arrived on the early blue planet aboard carbon-rich meteorites from space. In 2023, the Japan Agency for Marine-Earth Science and Technology analyzed samples of dust and gas brought back from an asteroid, presumably formed shortly after the creation of the solar system, called Ryugu. Initially They found uracilThis suggested that the bases of human RNA could be of extraterrestrial origin. Now the same team has published a study in Nature Astronomy In which they argue that this theory is strengthened, since they have now found the five nucleobases (the name given to these basic molecules).

The Japanese Hayabusa 2 mission collected 5.4 grams of dust and gas samples during two landings on Ryugu, an asteroid just over 900 meters in diameter, and brought them back to Earth in December 2020. These are samples taken directly from the surface of a contaminated asteroid—unlike those collected from meteorites. This is the oldest material that humanity has had access to so far, and the researchers' goal was to identify whether they contained the five organic building blocks of life. Therefore, scientists from the Japan Agency for Marine-Earth Science and Technology analyzed the Ryugu samples more thoroughly—using chemical extraction techniques and mass spectrometry, a scientific technique used to identify and measure molecules by analyzing their mass—and compared them with the material. orbiting near Earth) and the Orgueil (fallen in France) and Murchison (Australia) meteorites.

Researchers detected all five canonical nitrogenous bases in the two Ryugu samples, confirming that the molecular requirements for life are not unique to Earth and can arise as natural products of chemical evolution throughout the solar system. Furthermore, scientists found significant differences in the relative abundances of these building blocks in the different samples. Specifically, Ryugu contains roughly comparable amounts of purine nucleobases (adenine and guanine) and pyrimidine nucleobases (cytosine, thymine, and uracil). In contrast, Murchison has a higher presence of purine nucleobases, while Bennu and Orgueil are richer in pyrimidine.

"Coherent" finding

According to the researchers, this shows that these molecules, essential for life, can form naturally in space and that the chemistry of asteroids can vary depending on the environment in which they formed, for example, the amount of ammonia present. "[The finding] demonstrates their widespread presence throughout the solar system and reinforces the hypothesis that carbon-rich asteroids contributed to the prebiotic chemical inventory of early Earth," the authors explain. According to the study, nucleobases are common in the solar system and likely arrived on Earth via asteroids and meteorites, contributing to the set of molecules that allowed life to develop. "These results are consistent with what we ourselves have observed on Ryugu and in carbonaceous chondrite meteorites, and are consistent with everything already studied in previous work. This consistency is very important in science," argues astrobiologist and professor of biochemistry at the University of Alcalá, César Menor.

In fact, the scientific community has long known that nucleobases do not need life to form and that they can appear on asteroids without biological activity. Hence, Menor emphasizes that the study's conclusions are not "surprising or new," but rather "consistent" with everything that was previously known and observed, he explains in statements to SMC.