When the OSIRIS-REx probe brought samples to Earth in 2023 from the asteroid Bennu, a small rock measuring about 500 meters that orbits between Earth and Mars, few imagined that a handful of space dust could revolutionize our understanding of the origin of life. But a recent study, published in the Proceedings of the National Academy of Sciences, points out that They contain something much more valuable than primitive rock. There is an almost complete “chemical kit” of the necessary blocks for life.
Among the compounds detected are 14 of the 20 amino acids that we use on Earth to build proteins, as well as the five fundamental nucleobases of DNA/RNA (adenine, guanine, cytosine, thymine/uracil). Furthermore, the authors, led by Ángel Mojarro, identified traces of ammonia, salts compatible with ancient “brines” and a large amount of organic compounds rich in nitrogen.
But there is an even more interesting detail: when life on Earth began using amino acids, it did so almost exclusively with a chemical “hand,” a molecular configuration called left-handed. In Bennu, however, amino acids appear in an almost equal mix between “left” and “right” forms. This suggests that the chemical homogeneity of terrestrial life, the aforementioned preference for “one hand”, was not a prebiotic necessity, but something that life developed later, probably by evolutionary selection.
This set of findings (amino acids, nucleobases, salts, ammonia, complex organic matter) turns Bennu into what many call a “time capsule”: a testament to the chemistry of the early solar system, before the formation of planets, when the building blocks of life already existed in small, dusty bodies.
What does this discovery imply? The study gives several keys. The first of them is that the ingredients of life were not necessarily born on Earth: they could have come from space. If asteroids like Bennu bombarded Earth in its early days, they may have seeded amino acids, salts, organic compounds, and DNA/RNA precursors here.. This idea, known as “chemical panspermia” or “exogenous origin” of prebiotic molecules, is gaining strength.
It also allows us to assume that prebiotic chemical processes could occur in very small bodies, that is, planets, oceans or dense atmospheres are not needed to form complex organic blocks; All you need is water, salts, compounds rich in carbon and nitrogen, and suitable conditions. Bennu could have been part of a larger body with groundwater (“brine”), which favors prebiotic chemical reactions.
And finally, The discovery shows that life could be more common than we think: If asteroids and smaller bodies throughout the solar system (and perhaps other planetary systems) have similar chemistry, then the ingredients for life could be everywhere. That greatly expands the possibilities of extraterrestrial life.
However, it is worth remembering the essential thing: although Bennu has the ingredients, there is no evidence of life in it. The samples contain prebiotic compounds, but not cells, self-replicating structures or metabolic processes. The authors summarize it: “We know that the components for life were there, but not why life did not form on Bennu, nor why on Earth it did.”
What’s left to do? So far, only a fraction of the Bennu sample has been analyzed. Grams of regolith remain to be studied, and many analytical techniques have not yet been applied. Will there be more unknown amino acids? More complex molecules? Precursors for lipids, sugars, RNA-like structures? Besides, Scientists must investigate how these molecules originated: By purely chemical processes in the asteroid, by reaction in saline water, by radiation, by residual heat?
These types of questions are key to understanding not only if asteroids “seeded” life on Earth, but if they could do so on other worlds. In that sense, Bennu (and its chemical history) becomes a window into a distant past, and at the same time a beacon towards a possible future: one in which life is not a local rarity, but a natural consequence of the chemistry of the cosmos.