Scientists have identified tryptophan, an essential amino acid, within material collected from the asteroid Bennu. The finding comes from NASAs OSIRIS-REx mission, which gathered 121.6 grams of rocks and dust from the asteroid in 2020 and delivered the samples to Earth in 2023. Portions of this material have since been distributed to research teams for study.
Bennu is considered a valuable window into the early solar system. Earlier analyses of its samples revealed fourteen of the twenty amino acids used by life on Earth, along with all five biological nucleobases that form DNA and RNA. Similar discoveries were previously made in samples from asteroid Ryugu and in various meteorites, suggesting that asteroids could have supplied critical chemical ingredients to early Earth.
The new results add tryptophan to the list, raising the number of protein-forming amino acids found in Bennu to fifteen. Jos Aponte, an astrochemist at NASAs Goddard Space Flight Center and coauthor of a study published in PNAS, noted that tryptophans complexity makes its detection particularly significant. Its presence supports the idea that essential biochemical components formed naturally in space long before life emerged on Earth.
Bennu, named after an ancient Egyptian deity linked to creation and renewal, spans about one third of a mile in width. It likely originated from a larger parent asteroid and has been in Earths cosmic neighborhood for roughly 1.75 million years. Its material contains elements forged in ancient supernova explosions and shaped by heat, impacts, and solar radiation over billions of years. Researchers have also identified ammonia and a variety of minerals within the asteroid, providing many of the raw ingredients needed for prebiotic chemistry.
According to Angel Mojarro of NASAs Goddard Space Flight Center, lead author of the new study, these materials resemble scattered puzzle pieces that have not yet formed living systems. Detecting tryptophan broadens the set of amino acids known to form naturally in space and potentially reach Earth via asteroids or comets. Although further testing is required to confirm the result, experts believe the pristine nature of the Bennu samples makes contamination unlikely.
The OSIRIS-REx mission preserved the material without the chemical alteration that meteorites undergo when entering Earths atmosphere. This allowed scientists to examine fragile salts, minerals, and organic compounds that would not have survived a fiery descent. Researchers believe Bennus parent body once hosted multiple fluid-rich environments, each fostering its own chemical processes.
George Cody of the Carnegie Institution for Science, who was not involved in the study, said the findings strengthen the idea that the molecules essential to life may trace their origins to the earliest stages of the solar system. The late researcher Harold Morowitz once proposed that key biomolecules might be molecular remnants from that ancient era, and the discovery of tryptophan adds support to this concept.
Kate Freeman, a professor at Penn State University, noted that asteroids likely served as delivery systems for a wide range of organic compounds during Earths formative period. Sara Russell of the Natural History Museum in London added that sample return missions remain crucial for accessing uncontaminated materials, which cannot be fully replaced by meteorites alone. She emphasized that the absence of tryptophan in meteorites may be due to its destruction during atmospheric entry, making its detection in Bennu especially noteworthy.