When the Japanese Hayabusa2 probe dropped a small capsule in the Australian desert in December 2020, scientists knew that the few grams of dark dust it contained were worth their weight in gold. And it is no wonder, since they were intact pieces of the Ryugu asteroid, a space rock that six years later has reinforced one of the many theories of the origin of life: the building blocks of life arrived on Earth from space.
A genetic puzzle. It is not the first time that Ryugu gives us joy, since already in 2023 previous analyzes revealed the presence of uracil, which is one of the ‘letters’ that forms human RNA, and also vitamin B3. Now much more has been found.
A new study published in Nature Astronomy has confirmed the discovery of the ‘grail’ of prebiotic chemistry. Specifically, Ryugu’s samples contained the five canonical nucleobases that make up our genetic material, both DNA and RNA. We talk about adenine, guanine, cytosine, thymine and uracil. From all these letters, although it may seem too simple, both our DNA and that of other species in the ecosystem are formed.
How they have done it. It has been a team led by several Japanese institutions that has managed to identify the complete collection of genetic components using chromatography and mass spectrometry techniques. And, according to the study, these five nucleobases are found in surprisingly balanced proportions, something that differentiates Ryugu from other celestial bodies studied to date.
The genetic code. To understand the magnitude of the discovery, we must remember how our genetic code works and go back to high school. This is based on two types of molecules: purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil).
In previously analyzed meteorites (such as the famous Murchison) or even in samples from the asteroid Bennu, the proportions tended to be unbalanced, predominating one over the other. Ryugu, on the other hand, shows a balance that has led researchers to propose a new molecular indicator to understand how these nucleobases evolved non-biologically in deep space, based on the relationship between purines, pyrimidines and ammonia.
Pollution? It is the idea that may come to mind, since if we analyze a meteorite that has fallen to Earth, the logical thing could be that the rock became stained upon impact and dragged away part of living matter. But this is where the magic of the Hayabusa2 mission comes in: by collecting the sample directly from the asteroid in empty space and bringing it back in a sealed capsule, the possibility of contamination is ruled out.
Furthermore, the JAMSTEC scientific team has carried out extensive testing with isomers under hyper-controlled conditions, confirming that these nucleobases have an unequivocal extraterrestrial origin.
Its importance. This discovery does not confirm that there is life on the asteroid, but rather points to the asteroid being a carbon-rich “time capsule” that shows us the chemical inventory of our early solar system.
Billions of years ago, the Earth was an inhospitable place and the theory of panspermia suggests that carbonaceous asteroids like Ryugu acted as “cosmic taxis”, bombarding our young planet and depositing this molecular alphabet on it and providing it with the components from which life later emerged. But this is one of the many theories that are on the table to understand our most primitive origin.
Images | NASA Hubble Space Telescope
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