Studies Find Life’s Building Blocks in Bennu Asteroid Samples

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A large circular, metal container with samples of asteroid Bennu inside. A top-down view of the OSIRIS-REx Touch-and-Go-Sample-Acquisition-Mechanism head with the lid removed, revealing samples of asteroid Bennu inside. The sample material includes dust and rocks up to about 0.4 in (1 cm) in size.
NASA/Erika Blumenfeld & Joseph Aebersold

Two new studies out this week find that rock and dust samples retrieved by NASA from the asteroid Bennu in 2023 contain some of the building blocks for life on our planet—as well as evidence of underground pools of saltwater that might have served as the “broth” for these compounds to interact and combine.

The studies, published in Nature Astronomy and Nature, are the first in-depth analyses of the minerals and molecules on Bennu, a remnant of a larger celestial body that formed about 4.5 billion years ago. The findings indicate that asteroids like Bennu may have seeded early Earth with the raw ingredients that led to the emergence of life. 

“Scientists have long thought that the compounds that make life on Earth possible arrived in meteorites after originating on distant, ancient bodies, like the one from which Bennu descended,” said Museum Research Associate Harold C. Connolly Jr., who is also the mission sample scientist for OSIRIS-REx and a professor at Rowan University. “Linking the organic abundances to rocks that contain a suite of evaporite minerals, or salts, is a first and is a critical piece to the puzzle. This work is further confirmation that asteroids are the building blocks of planets, and they carry the building blocks of life.” 

Connolly oversees work of the sample analysis phrase of the OSIRIS-REx mission, which includes about 260 researchers from more than 40 institutions. 

The Nature Astronomy study, led by NASA, detected 14 of the 20 amino acids that life on Earth uses to make proteins—and all five nucleobases that life on Earth uses to store and transmit genetic instructions in more complex terrestrial biomolecules, such as DNA and RNA. These molecules have been found before in meteorites recovered on Earth, but the NASA mission sought out a pristine sample because meteorites degrade when they breach Earth’s atmosphere. 

A false-colored close-up on the Bennu asteroid sample depicting hydrated sodium carbonate needles in a brighter color beside pale clumps.
Researchers identified salt minerals in the Bennu samples that were deposited as a result of brine evaporation from the asteroid’s parent body. In particular, they found a number of sodium salts, such as the needles of hydrated sodium carbonate highlighted in purple in this false-colored image.
Rob Wardell/Tim McCoy/Smithsonian Institution; colorization: Heather Roper/University of Arizona

“The clues we’re looking for are so minuscule and so easily destroyed or altered from exposure to Earth’s environment,” said Danny Glavin, a senior sample scientist at NASA’s Goddard Space Flight Center and co-lead author of the Nature Astronomy paper. “That’s why some of these new discoveries would not be possible without a sample-return mission, meticulous contamination-control measures, and careful curation and storage of this precious material from Bennu.” 

The Nature study, led by scientists at Smithsonian’s National Museum of Natural History and the Natural History Museum in London, describes clues about the environment in which these molecules would have formed. Scientists identified traces of 11 minerals in the Bennu sample including calcite, halite, and sylvite. These minerals form when water containing dissolved salts evaporates over long periods of time, leaving behind the salts as solid crystals. 

Brines like this have been detected or suggested in other parts of the solar system, including on the dwarf planet Ceres and Saturn’s moon Enceladus.