The metal container fell in the middle of the U.S. desert in Utah in September 2023. It came from outer space and its oval shape resembled what we imagine a UFO to look like; it was not an extraterrestrial object, but this kind of vessel designed by NASA engineers for the OSIRIS-REx space mission did carry inside material that is not from our planet: pristine rocks and dust collected from the surface of the asteroid Bennu in 2020 and brought to Earth.
Quickly, a team from NASA headed to the container to prevent the capsule containing the samples collected from Bennu from being contaminated or altered when exposed to our planet's climate. Inside was a true gem for science: 121.6 grams specifically brought from a celestial body in its natural environment.
We mention the exact figure because in a mission as complex and delicate as this one, every gram of extraterrestrial material matters. And the OSIRIS-REx spacecraft, which arrived at Bennu in 2018, was able to collect twice the amount that NASA had set for the mission. An achievement that has allowed scientific teams from various places around the world to obtain part of these samples and analyze them with the ultimate goal of understanding how the Solar System was formed and how the water and necessary elements for life arrived on our planet.
This Wednesday, the research of two teams that have analyzed in detail the chemical composition of Bennu is published simultaneously, offering new information about what the Solar System is made of.
Bennu has always intrigued researchers due to its proximity to Earth's orbit and its carbon-rich composition. They thought that this asteroid contained traces of water and organic molecules, and their hypothesis is that asteroids similar to Bennu could have brought all these materials to Earth during its formation stage.
After passing the samples through the most advanced instruments, scientists have had some surprises. The rocks and dust from this asteroid contain organic matter, including amino acids and all nucleobases, as well as abundant salts that formed in the early stages of the parent celestial body - from which Bennu originated.
The first of the studies, published in the journal Nature Astronomy and led by Daniel Glavin, describes the discovery of thousands of molecular organic components, including 14 of the 20 amino acids of proteins present in different types of living organisms on Earth. They have also detected another 19 non-protein amino acids that are rare or do not exist in known Earth biology, and the five nucleobases (adenine, guanine, cytosine, thymine, and uracil).
They have also seen that the asteroid is rich in nitrogen and compounds containing ammonia, which must have formed billions of years ago in cold and distant regions of our solar system. The organic matter is more complex than Earth's biology and suggests that its parent body may have come from the outer Solar System, where ammonia and volatile ices are stable. Some of the compounds found in this analysis have not been observed in meteorites that have fallen on Earth.
The other research is published in the journal Nature, and in it, Timothy McCoy and his colleagues from the Smithsonian National Museum of Natural History in Washington describe a variety of mineral salts found on the asteroid, including phosphates containing sodium and carbonates, sulfates, chlorides, and sodium-rich fluorides. This team believes that these salts could have formed during the evaporation of water pockets that must have existed in Bennu's parent body during the early stages of Solar System formation, about 4.5 billion years ago.
As the water evaporated, these minerals formed, including components that had not been observed in any other extraterrestrial body samples until now. Their hypothesis is that these extraterrestrial minerals would have formed in a similar way to how it happens in some supersaline lakes on Earth or in the subsurface oceans of the dwarf moons of the Solar System, such as Enceladus (a moon of Saturn) and in dwarf planets like Ceres.
Bennu's brine differs from Earth's brines in its composition. The asteroid samples are rich in phosphorus, which is abundant in meteorites and relatively scarce on Earth. On the contrary, they have little boron, very common in Earth's hypersaline lakes but extremely rare in meteorites.
The discovery suggests that extraterrestrial brines provided a crucial environment for the development of organic compounds.
"Thanks to Bennu, we know that the raw elements for life combined in very complex and truly interesting ways in the parent body of this asteroid," explains Tim McCoy, curator of meteorites at the Smithsonian Museum and co-leader of this research. "We have found something we did not expect, and that is the best reward for any kind of exploration," he points out.
The potential presence of water, combined with nucleobases, raises the question about the potential for the process that creates the basic components of life, a question that, according to the researchers, requires further investigation. Because although the authors believe that these extraterrestrial brines are crucial for the development of organic components by containing an intriguing set of minerals and elements, it is not clear if the environment was suitable for converting those ingredients into highly complex organic structures.
"The article is magnificent and one of the most comprehensive and innovative studies that, in my opinion, have been published to date on asteroids of this type," summarizes planetary geologist Jesús Martínez-Frías, an expert in Meteorites, Planetary Geology, and Astrobiology at the Spanish National Research Council (CSIC) and a member of the Astrobiology Commission of the International Astronomical Union (IAU).
Minerals from the Smithsonian National Museum of Natural History collection also found on the asteroid BennuGreg Polley/Smithsonian
For this planetary geologist, "the identification of a set of salts related to geological processes linked to the presence of water, along with all the identified organic compounds, represents a very important qualitative leap in understanding the complexity of interactions in the primitive Solar System between brines and original materials."
"With all that has been detected, we are just one step away from that enigmatic transition between all the fundamental ingredients (basic building blocks) for life to emerge. And we already find them in space," says Martínez-Frías, who considers that "the relationships between planetary geology, prebiotic chemistry, and astrobiology are becoming increasingly close."