When the OSIRIS-REx mission capsule landed in the Utah desert in September 2023, NASA knew it had a treasure on its hands. We are talking about a bit of black dust that was collected millions of kilometers from Earth and that was about to rewrite one of the most important chapters in science: the origin of life.
What we knew. Until now, the prevailing theory regarding the origin of life told us that to “cook” all the basic components of life, such as amino acids, heat and liquid water were needed to make a kind of hot chemical soup.
However, science has just flipped the script: the bricks of life are not only formed in heat, but can be born in the most extreme cold and under gamma radiation. And that completely changes our understanding of how we got here, and also of the possible presence of life in any corner of the Universe.
The importance of Bennu. It is undoubtedly the protagonist of this entire story, and it is nothing more than an asteroid about 500 meters in diameter that functions as a fossil from the primitive solar system. But the most interesting thing is that it is approximately 4.6 billion years old, the same age as the Earth, although, unlike our planet, its surface has not melted or been drastically altered by geological processes throughout its ‘life’.
And little by little we are learning more about this asteroid thanks to the samples brought back by OSIRIS-REx that had already confirmed in preliminary analyzes an unusual abundance of carbon, nitrogen, water and organic compounds. But what the team led by Penn State University has now found goes one step further.
The surprise. This same team, when analyzing the isotopic composition of the amino acids present, especially glycine, came across a chemical signature that did not fit with the classical theory of formation in hot water.
A radioactive freezer. Until now, we thought that amino acids in asteroids were formed primarily through aqueous alteration processes: ice melts from heat, liquid water interacts with rock, and voilàcomplex organic chemistry.
However, science now suggests that liquid water is not necessary for amino acids, an essential molecule of life, to form. Simply from simple ice they can arise without much problem. And there are many of these in the universe.
The catalyst. The other important factor in this formation was energy, which in this case came from gamma radiation emitted by radioactive elements that were abundant in the early solar system. And the energy could not come from thermal heat, since this process occurs in icy environments, long before the asteroid was compacted or heated enough to have liquid water.
This explains why we found amino acids both in asteroids that underwent a lot of water heating and in those that remained “drier” and colder. Life, it seems, is more stubborn than we thought and can begin to develop in the most hostile conditions of the vacuum of space.
An increasingly complex menu. But we are not just talking about simple molecules, since analyzes of Bennu samples have identified a variety of compounds. Among these is tryptophan, which is an essential amino acid, much more structurally complex, and vital for terrestrial life.
In addition, DNA and RNA components have been detected, as well as ammonia and amines, surpassing in richness many samples of famous meteorites such as Murchison.
Backlash to Panspermia. If amino acids can easily form in irradiated ice grains in the solar nebula—before the planets even formed—it means that these “ingredients” are spread throughout the solar system.
The fact that Bennu, a B-type carbonaceous asteroid, is packed with these compounds reinforces the idea that Earth didn’t have to produce all the components of life itself. A steady shower of asteroids and meteorites during the late intense bombardment may have “seeded” our planet with a prefabricated deep-space biological starter kit. That is why in the end looking at a grain of Bennu dust is looking at ourselves. Or, at least, to the chemical great-great-grandparents who made us here today.
Images | NASA Hubble Space Telescope
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