A new analysis of samples from the asteroid Bennu, NASA's first asteroid sample captured in space and delivered to Earth, reveals that evaporated water left a briny broth where salts and minerals allowed the elemental ingredients of life to intermingle and create more complex structures. The discovery suggests that extraterrestrial brines provided a crucial setting for the development of organic compounds.
In a paper published on January 29 in the journal Nature, scientists at the Smithsonian's National Museum of Natural History describe a sequence of evaporated minerals that date back to the early formation of the solar system. The assortment of minerals includes compounds that have never been observed in other extraterrestrial samples.
According to Tim McCoy, the museum's curator of meteorites and co-lead author on the new paper, the findings indicate that the raw ingredients of life were combining in complex ways on Bennu's parent body. Bennu's parent asteroid, formed around 4.5 billion years ago, appears to have contained pockets of liquid water.
The new findings suggest that water evaporated, leaving behind brines resembling the salty crusts of dry lakebeds on Earth. NASA's OSIRIS-REx spacecraft collected samples from Bennu in 2020, marking the first U.S. mission to collect a sample from an asteroid's surface.
Upon returning to Earth, the capsule containing the samples touched down in the Utah desert, where scientists were ready to retrieve it. In total, OSIRIS-REx collected approximately 120 grams of material, which has been distributed to researchers worldwide for analysis.
Surprisingly, traces of water-bearing sodium carbonate compounds were found in the Bennu samples. These compounds, also known as soda ash or trona, have never been directly observed in other asteroids or meteorites. The findings suggest that similar brines may exist on other extraterrestrial bodies, including the dwarf planet Ceres and Saturn's moon Enceladus.
While the Bennu brines contain intriguing minerals, it remains uncertain if the local environment was suitable for crafting these ingredients into complex organic structures. McCoy noted that while the basic building blocks for life have been identified, the extent to which they could evolve remains unknown.
Two concurrent studies published on January 29 in the journal Nature Astronomy provide additional insights into Bennu's composition, including the discovery of amino acids and nucleobases that form RNA and DNA.
These studies represent significant progress in understanding the origins of life and the role of asteroids like Bennu in making Earth habitable.