A groundbreaking discovery has revealed the presence of tryptophan, an essential amino acid, on the asteroid Bennu. This finding is part of the remarkable insights gained from NASA’s OSIRIS-REx mission, which successfully collected samples from Bennu in 2020 and returned them to Earth in September 2023. These samples have provided scientists with vital information about the building blocks of life and the early solar system.
The analysis of the Bennu samples indicates that tryptophan is among the 15 out of 20 amino acids essential for life. This discovery was confirmed by a study published on March 11, 2024, in the journal Proceedings of the National Academy of Sciences (PNAS). According to José Aponte, an astrochemist at NASA’s Goddard Space Flight Center and coauthor of the study, “Finding tryptophan in the Bennu asteroid is a significant development because it had never been observed in any meteorite or space sample before.”
Implications for Understanding Life’s Origins
The presence of tryptophan supports the theory that the ingredients for life may not have originated solely on Earth. Aponte explained, “Seeing it form naturally in space tells us that these ingredients were already being made out in the early Solar System. That would have made it easier for life to get started.” Prior to this finding, researchers had identified 14 of the 20 amino acids essential for life in Bennu samples, as well as all five nucleobases that compose DNA and RNA.
Bennu, which is approximately 500 meters wide, is believed to be a remnant from the early solar system, formed around 4.5 billion years ago. It has been orbiting close to Earth for approximately 1.75 million years. Current estimates suggest it could potentially collide with Earth in 2182, with a 0.037% chance of impact, potentially resulting in a “global winter.”
The elemental composition of Bennu, derived from ancient supernovae, showcases the complex processes that contribute to the formation of amino acids and other organic compounds. Angel Mojarro, a postdoctoral researcher and first author of the study, noted, “They’re like jigsaw pieces that are not yet assembled. What this is telling us is that many of the building blocks of life can be produced naturally within asteroids or comets.”
Future Research and the Importance of Sample Return Missions
Despite the promising results, further tests are necessary to confirm the presence of tryptophan in the analyzed sample, which weighed just 50 milligrams. George Cody, a staff scientist at the Carnegie Institution for Science, emphasized the significance of the pristine condition of the Bennu samples, stating, “I believe these molecules are legitimately derived from the Bennu asteroid.” The OSIRIS-REx mission has provided scientists with uncontaminated material, allowing for a clearer analysis of the asteroid’s chemical composition.
The findings also highlight the essential role of sample return missions in advancing our understanding of extraterrestrial materials. Sara Russell, a professor of planetary sciences at the Natural History Museum in London, remarked on the rarity of tryptophan in meteorite samples, suggesting that it may not survive the transition through Earth’s atmosphere.
This discovery of tryptophan adds to the growing body of evidence that asteroids can deliver critical life-sustaining compounds to planets. Kate Freeman, an Evan Pugh University Professor at Penn State University, noted that “Asteroids were the early Earth’s grocery delivery service, having provided a wealth of molecules to our prebiotic world.”
The insights gained from Bennu not only enhance our understanding of life’s origins but also emphasize the potential for further discoveries from ongoing research into asteroids and other celestial bodies. As scientists continue to analyze samples from Bennu and other sources, they are piecing together the complex puzzle of how life may have emerged in our universe.
