© Javier Miranda/Unsplash
320 million kilometers from our planet, the asteroid Bennu keeps in its breast the secrets of the first moments of our solar system. NASA's OSIRIS-REx mission has just uncovered some of them, thanks to the analysis of samples brought back to Earth in September 2023. The results of these have been published in two papers ;: one in the journal Nature Astronomyand the other in Nature.
Bénou and its 525 meters in diameter is in reality a real natural laboratory of prebiotic chemistry (the study of chemical reactions that could have led to the formation of the first living molecules), in which the fundamental ingredients of life are indeed present. For NASA, it is a resounding success.
The salts of Benu: evidence of primitive aqueous activity
The NASA scientists who recovered these 120 g of dust collected on Benu managed to identify, using electron microscopes, two particularly important minerals. The first, halite, the mineralogical name for rock salt, which is mainly composed of sodium chloride (NaCl). It is the same salt that we use daily in our kitchens.
The second element is sylvite, a mineral composed of potassium chloride (KCl), mainly used in the production of fertilizers because of its richness in potassium, an essential element for plant growth.
These salts, extremely rare in meteorites – they are found in only three specimens out of several hundred thousand – are valuable indicators. Indeed, their presence is evidence that Bennu likely experienced interactions with liquid water in the past.
Since water is an essential ingredient for life as we know it, its presence, even in the past, suggests that this asteroid may have once been a favorable environment for prebiotic chemistry. That is, the chemistry that may have led to the emergence of life.
The researchers also discovered other precious minerals, telling us about Bennu's history and the chemical processes that took place there. Sodium carbonates, similar to those that form in terrestrial salt lakes, phosphates, compounds essential for energy storage in biological systems, and sulfates/fluorides, which, on Earth, play a role in many geochemical processes.
This mineralogical assemblage indicates that Bennu's parent body; itself a fragment of a larger celestial body; underwent a period of aqueous activity, during which salt solutions evaporated, leaving behind these characteristic deposits.
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200% Deposit Bonus up to €3,000 180% First Deposit Bonus up to $20,000A primitive soup rich in living molecules
In addition to these rare salts, Bénou has been found to be particularly rich in organic compounds, complex molecules containing carbon, which are also essential to life and many chemical processes. Among them, we can cite 14 of the 20 amino acids used by terrestrial life. These are the building blocks of proteins, molecules that are fundamental to life. The discovery of these organic molecules shows that the basic elements of life can therefore form in space and be present on celestial bodies such as asteroids.
Another discovery: all five nucleobases that make up RNA and DNA. If we imagine that these are like long brick walls that contain all the information needed to build and operate a living being. Nucleobases are the bricks that make up these walls. Finding them on the surface of Bennu thus means that the molecules that carry the genetic information of all living beings, also exist outside of Earth.
A third compound contained in the sample: ammonia (NH3). An important source of nitrogen, it is also an essential element for life. Nitrogen is a building block of amino acids, proteins, and nucleotide bases (the building blocks of DNA and RNA).
The presence of these organic molecules thus suggests that similar processes may have occurred on other celestial bodies, thus increasing the possibility that life exists elsewhere in the Universe.
These very encouraging results will shed new light on research on other celestial bodies, including Enceladus, a satellite of the great Saturn, and Ceres, a dwarf planet in the asteroid belt. Both worlds harbor brine oceans (bodies of extremely salty water) beneath their icy surfaces, in conditions potentially analogous to those that existed on Bennu's parent body.
For the moment, investigations continue, and the scientists' work will focus on the precise dating of the fragmentation of Bennu's parent body and on the traces of impacts recorded in the mineral composition of the samples. If no trace of life has been directly detected, this does not mean that the search is in vain. These analyses demonstrate that the chemical conditions necessary for the formation of living molecules already existed at the earliest moments of the solar system, more than 4.568 billion years ago. The other theory reinforced by these recent discoveries: life could have an extraterrestrial origin (panspermia). Asteroids or comets, such as Bennu, may have brought these organic molecules to Earth billions of years ago, contributing to the emergence of the first living organisms.
- Asteroid Bennu contains rare salts and organic compounds suggesting ancient aqueous activity that supported prebiotic chemistry.
- Samples revealed amino acids, nucleobases, and ammonia, key building blocks for life, that are present outside Earth.
- These findings reinforce the idea that celestial bodies like Bennu may have seeded the foundations of life on Earth and elsewhere in the Universe.
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