The identification of tryptophan on the asteroid Bennu It has become one of the most striking findings in recent astrobiology. For the first time, a complex essential amino acid, popularly known for being present in foods like turkey, appears convincingly in extraterrestrial material collected directly and in almost pristine conditions.
The result comes from the samples that the mission NASA's OSIRIS-REx It was brought back to Earth from Bennu, a small nearby asteroid considered a veritable time capsule of the early Solar System. The discovery not only expands the catalog of organic compounds detected outside our planet, but also reinforces the idea that The basic ingredients of life could be manufactured and travel through space long before the Earth was habitable.
What is Bennu and why is this asteroid of such interest to astrobiology?
Bennu is a carbon-rich asteroid about 500 meters in diameter It passes relatively close to Earth approximately every six years. All indications are that it is a fragment that broke off from a larger body originally located in the main asteroid belt, between Mars and Jupiter, which formed billions of years ago.
Its chemical composition preserves traces of the processes that acted in the early Solar System: remnants of ancient supernovae, hydrated minerals, salts and organic compounds that were modified over time by internal heat, the melted ice and solar radiation. For scientists, studying Bennu is like opening a window to the early chapters of chemical history of our cosmic neighborhood.
Furthermore, orbital data indicate that Bennu repeatedly approaches Earth's orbit And that, although the probability is low, there is a small possibility of impact at the end of the 22nd century. This interest in its trajectory adds to the scientific interest in its composition, which explains why it was chosen as the target of a mission as complex as OSIRIS-REx.
For Europe, and particularly for the Spanish scientific community, Bennu also represents an opportunity. Researchers from Institute of Astrophysics of the Canary Islands and European centers They participate in the analysis of similar organic compounds in star-forming regions, connecting what is seen in the laboratory with what is detected in interstellar space.
The OSIRIS-REx mission: how the Bennu samples were obtained
Probe OSIRIS-REx (an acronym for Origins, Spectral Interpretation, Resource Identification and Security) took off with a very specific objective: Touch the surface of Bennu, collect regolith, and bring it home.After several months of maneuvering around the asteroid, the spacecraft approached in October 2020 and, through a brief contact with its robotic arm, captured dust and rock fragments.
In total, the mission achieved 121,6 grams of materialA record amount for this type of project. The capsule with the sample landed on Earth in 2023, and from there, NASA began distributing small portions to research teams around the world, including European groups specializing in extraterrestrial organic chemistry.
A key part of this success lies in the way the sample has been preserved. The regolith did not pass through Earth's atmosphere like a meteoriteTherefore, it did not undergo the extreme heating or chemical alterations typical of space rocks falling to Earth. Nor was it exposed to Earth's air or water beyond extremely controlled protocols.
For astrobiology experts, this makes the Bennu samples pristine materialalmost free of contamination. This purity is key when trying to detect delicate molecules like tryptophan, which are easily destroyed in harsh conditions or mistaken for terrestrial contaminants.
In the specific case of the study where tryptophan was identified, the fraction analyzed was minuscule: only about 50 milligramsEven so, the sensitivity of the instruments has been sufficient to obtain clear chemical signals that there was something more there than the amino acids already known.
How tryptophan has been detected in Bennu material
The new scientific work, published in the journal Proceedings of the National Academy of Sciences (PNAS)He combined two complementary techniques to scrutinize the array of organic compounds present in various fragments of the asteroid. The goal was to construct as complete a picture as possible of Bennu's internal chemistry.
On one hand, it was applied flash pyrolysisThis method heats the material very rapidly, releasing gases and compounds that had been trapped in the rock. These molecules are then identified by their fingerprint in a chromatogram and mass spectra, something like a chemical ID.
On the other hand, techniques were used to wet chemistryThese techniques are designed to disassemble and slightly modify organic molecules in order to reconstruct their structure and configuration. This strategy is especially useful for distinguishing between different types of amino acids and for detecting compounds present in minute quantities.
By cross-referencing the results of both approaches, the team found a catalog of organic compounds consistent with previous studies of carbon-rich meteorites, but with a new detail: weak but consistent signals pointing to a fifteenth amino acid On Bennu, tryptophan. Until now, this amino acid had never been reliably reported in meteorites or other samples returned from space.
The researchers insist that, although the level of confidence is high, Further analysis is still required. with even stricter cleaning protocols to definitively rule out any trace of terrestrial contamination. But the consistency of the signals in different experiments and the purity of the samples lead many specialists to consider the finding very solid.
Why is tryptophan so important in this context?
Tryptophan is one of the 20 amino acids used by life on Earth to produce proteins, and belongs to the group known as essential amino acids, those that our body cannot synthesize and that, therefore, we must obtain through food.
From a chemical point of view, it is one of the more complex amino acidswith an aromatic ring that participates in key reactions and helps stabilize the structure of many proteins. Furthermore, it is a precursor to molecules such as Serotonin, related to mood and sleep, which has fueled the popular association between holiday turkey and drowsiness.
Finding tryptophan, even in trace amounts, suggests that the The chemistry that occurred in small bodies like Bennu was able to generate a very broad repertoire of amino acidsnot limited to the simplest ones. On Earth, these complex amino acids are fundamental for cell function and protein diversity.
Until this new result, investigations on Bennu had already confirmed the presence of 14 amino acids used by living organismsIn addition to the five nucleobases of DNA and RNA, the addition of tryptophan raises to 15 the number of protein-forming amino acids detected on the asteroid, which, from an astrobiological perspective, is a significant step.
Several specialists, including astrochemists at Goddard Space Flight Center And scientists from European institutions emphasize that this type of finding reinforces the hypothesis that The building blocks of life were generated naturally in many different spatial environmentsand not exclusively on the surface of our planet.
A chemically diverse asteroid: water, salts, and organic matter
Analysis of the samples has shown that Bennu is far from being a homogeneous object. The proportions of soluble and insoluble organic compounds change from one stone to another, indicating that the original body from which the asteroid emerged underwent different internal geological processes.
The data suggests that inside that parent body Liquid water circulated unevenlygenerating a heterogeneous aqueous alteration. In some areas, certain types of hydrated minerals and salts formed, while in others, more complex hydrocarbons, such as polycyclic aromatic hydrocarbons, predominated.
This mixture of salts, ammonia, minerals and organic matter It resembles what is observed in carbonaceous chondrites, a type of meteorite extensively studied in European laboratories. The difference is that the Bennu samples arrive without the scars of atmospheric entry, thus preserving fragile components that typically disappear in meteorites.
Researchers involved in the mission emphasize that the Bennu's parent body must have been a small, active geological world.with several liquid systems operating at different times and places, each driving its own chemistry. Bennu would have inherited and preserved part of that mosaic of environments.
If different regions of the same asteroid offer varied chemical microenvironmentsThe likelihood increases that increasingly complex molecules will assemble in some of them. For European astrobiology, this scenario fits well with the idea that small bodies in the Solar System were veritable chemical “laboratories” for hundreds of millions of years.
Left-handed and right-handed amino acids: what Bennu tells us about the chirality of life
One of the most curious aspects of the amino acids found in Bennu is that They appear in racemic mixturesThat is, with similar quantities of "left-handed" (L) and "right-handed" (D) versions. Although the chemical formula is the same, the spatial arrangement is a mirror image, something that has important consequences in biology.
On Earth, life uses almost exclusively the left-handed (L) version of amino acids to build proteins, an asymmetry that remains one of the classic enigmas of the origin of life. That the Bennu samples show a balanced mix of L and D suggests that This biological preference was not imposed from the beginning due to the chemistry of the Solar System.
Rather, everything points to the choice of a single “side” It occurred in later stages, perhaps on Earth itself, under very specific physical or environmental conditions. This type of clue is especially interesting for European groups modeling the origin of homocirality in prebiotic systems.
In any case, the presence of racemic mixtures on Bennu reinforces the idea that, before life appeared as we know it, The catalog of available molecules was much more neutral. From the point of view of chirality. The asymmetry, therefore, could be a consequence of local processes rather than a global property of the spatial environment.
For those wondering what implications this has for the search for life beyond Earth, the interpretation is clear: We cannot assume that other worlds will use exactly the same molecular “side”. that our biology, although they share the same basic types of organic molecules.
Asteroids as messengers: could life have arrived on Earth riding on the backs of Bennu and its relatives?
For decades, various research groups have been working with a suggestive hypothesis: that the asteroids and comets acted as transport vehicles of prebiotic compounds to the early Earth. The new results from Bennu lend further weight to that idea.
The fact that they were found on this asteroid amino acids, nucleobases, ammonia, and waterAll of this in an environment that preserves traces of ancient brines, fits well with the scenario of a "cosmic delivery" of key ingredients for the chemistry of life.
Previous research on other bodies, such as the asteroid Ryugu Samples from the Bennu meteorite—whose samples were returned by the Japanese space agency—and numerous carbonaceous meteorites being studied in laboratories in Europe and the United States had already shown the presence of various amino acids. Bennu, however, provides a richer and better-preserved repertoire.
Some experts have described these smaller bodies as a “delivery service” of molecules that bombarded the Earth's surface during its first few hundred million years. During that time, large quantities of organic compounds were able to accumulate in oceans, ponds, and rocky surfaces, facilitating increasingly complex reactions.
From the perspective of European research, this view has clear implications for the study of exoplanets and young planetary systems: if The natural chemistry of space routinely produces the same building blocks used by life on Earth.It is reasonable to consider that similar processes might be occurring in other parts of the galaxy.
Connections with observations in interstellar clouds and star-forming regions
The discovery of tryptophan on Bennu is linked to work being carried out in Europe in the field of infrared and millimeter-wave astronomy. Teams from Institute of Astrophysics of the Canary Islands and other institutions They have identified tryptophan signatures in star-forming regions, such as the Perseus molecular complex.
In the area known as IC348For example, emission lines consistent with this amino acid have been detected in space telescope data, suggesting that Complex molecules are already forming in clouds of gas and dust long before mature planetary systems emerge.
That the same type of molecule appears in both distant interstellar environments The presence of amino acids on a near-Earth asteroid like Bennu supports the idea of a chemically prolific universe. An exceptional environment wouldn't be necessary for essential amino acids to appear; the conditions that occur naturally in molecular clouds and bodies rich in ice and carbon would suffice.
For the European scientific community, these results are an incentive to search for other amino acids and prebiotic compounds in different regions of the Milky Way. The more examples that accumulate, the harder it will be to argue that Earth is a chemical anomaly.
Combining laboratory analysis of Bennu samples With astronomical observations from telescopes located in the Canary Islands, Chile, or space, it offers an integrated view: from the interstellar cloud to the habitable planet, passing through asteroids that function as intermediate stages.
The role of Europe and Spain in the research of Bennu and prebiotic compounds
Although the OSIRIS-REx mission is led by NASA, European participation in the analysis The significance of the samples and their astrophysical context is considerable. Institutes in France, Germany, Italy, the United Kingdom, and Spain are collaborating on the study of minerals, organic compounds, and spectral signatures associated with the compounds detected on the asteroid.
In Spain, centers like the Institute of Astrophysics of the Canary Islands Universities with astrochemistry and planetary geoscience groups are closely following these results, building on their previous experience in the study of meteorites and regolith analoguesAlthough most of the material from Bennu is analyzed in the United States, the resulting data is shared internationally.
Furthermore, Europe is promoting its own exploration and sample return missions, such as the future Japanese-European mission MMX to the moons of Mars or ESA's plans to bring Martian material back to Earth in collaboration with NASA. The experience gained with Bennu will serve as a guide for designing protocols for collecting and preserving fragile compounds.
For European citizens, these advances are not just headlines about an exotic asteroid: they fuel research in chemistry, physics and biology which then translate into new analytical techniques, improvements in instrumentation and training of specialists in cutting-edge fields.
In the educational and outreach context, the story of tryptophan on Bennu offers a concrete and relatable example to explain How the origin of life is being investigated from Europe, with teams working side by side with colleagues from other continents on a topic that, deep down, challenges us all: where we come from and what place we occupy in the cosmos.
What remains to be discovered about Bennu and tryptophan
Despite the eye-catching headline, the researchers themselves insist on maintaining a degree of caution. The next step will be independently confirm the presence of tryptophan through new analyses of other fractions of the sample, using even more demanding methods in terms of contaminant control.
Furthermore, there is an ongoing effort to to better map the internal diversity of Bennu: relate in detail which minerals, salts and types of organic matter appear together and what clues they give about the physical conditions (temperature, pressure, presence of water) in which they were formed.
Scientists also compare these results with what has been observed in other bodies, such as Ryugu and certain meteorites, to see if the “menu” of amino acids and nucleobases found on Bennu is exceptional or represents a norm among carbon-rich asteroids.
Much of the material returned by OSIRIS-REx will be preserved long-term in specialized facilities, pending analysis techniques that do not yet existThe experience with lunar samples from the Apollo missions, which decades later continue to yield surprises thanks to new tools, suggests that Bennu will continue to provide data for many years to come.
Although we don't yet have all the answers, the picture that is emerging is that of a universe capable of producing and dispersing everywhere the chemical ingredients of lifeleaving the planets with the task of organizing those ingredients into increasingly complex biological systems.
What the dark rocks What Bennu has to offer is that the boundary between the “inanimate” chemistry of space and the biochemistry The structure that sustains living things is less clear than we thought; with tryptophan and other amino acids traveling on asteroids, Earth must have received an abundant supply of molecular building blocksAnd that early provision may have made all the difference on the long road that led from simple organic compounds to the diversity of life we know today.
