The latest research from Pennsylvania State University in the United States shows that trace dust samples from the asteroid "Bennu" are changing the scientific community's traditional understanding of how the basic components of life were formed in the universe. The research team confirmed the presence of a variety of amino acids in the approximately 4.6 billion-year-old asteroid rock. These samples were successfully collected and brought back to Earth by NASA's "OSIRIS-REx" probe in 2023, confirming that the basic raw materials for life are indeed widely present on extraterrestrial bodies. However, the chemical pathway through which these molecules are born in space has been an open question before.
New results published in the Proceedings of the National Academy of Sciences (PNAS) point out that some of the amino acids in the "Bennu" sample are not formed in the way that the scientific community has long assumed. Research shows that they were likely born in an extremely cold, radiant icy environment, rather than in an environment with warm liquid water. This conclusion means that the conditions for the formation of amino acids, the "building blocks" of life, are much looser and more diverse than previously imagined. There may be more seemingly harsh corners of the universe that still have the potential to breed raw materials for life.
Allison Baczynski, co-first author of the paper and assistant research professor in the Department of Earth Sciences at Penn State, said that this discovery "overturns our traditional view of how amino acids are produced on asteroids," showing that amino acids are not limited to the formation of warm, watery environments, but can be born in a variety of different pathways and conditions.
In order to uncover the secrets of the chemical composition of "Bennu" dust, the research team only used about "one teaspoon" of precious samples and relied on special instruments to conduct detailed analysis of the isotopic composition. These instruments measure minute differences in the atomic masses of elements, providing "fingerprints" that can trace the history of chemical reactions. The analysis focused on the simplest amino acid, glycine, a molecule consisting of only two carbon atoms that is regarded as an important marker for tracing the chemistry of prebiotic life.
Amino acids can be linked together to form proteins, and proteins are involved in almost every biological function, from building cell structures to catalyzing chemical reactions. Glycine has a simple structure and diverse production pathways, so if it is found on comets or asteroids, it will often strengthen the idea that some of the first chemical raw materials for life may have been synthesized in interstellar space long before the formation of planets, and transported to the surface of the young Earth through meteorites and dust.
In the past mainstream model, scientists generally believed that amino acids were mainly produced through the so-called "Strecker synthesis": hydrocyanic acid, ammonia, and aldehydes or ketones react in a liquid water environment to form amino acid molecules. However, the isotopic signature of Bennu's samples points to a completely different path. The researchers found that the isotope ratios of these glycines are not consistent with the classic water phase chemical pathway, and are more consistent with the results of complex reactions in low-temperature ice layers and under strong radiation, suggesting that they may have originated from the icy regions of the outer solar system in the early solar system.
Bachinski pointed out that Penn State University has specially modified the analytical instrument to enable it to measure isotopes in extremely low-abundance organic matter; without this technological breakthrough, this discovery may not have been achieved at all. Team members involved in the research include Earth Sciences Professor Christopher House, "Ivan Pugh University Professor" Katherine Freeman, postdoctoral researcher Ophélie McIntosh, and Earth Sciences doctoral student Mila Matney.
To further understand the uniqueness of the amino acids on Bennu, the researchers compared it with amino acids in the famous Melbourne County meteorite, the Murchison meteorite. The Murchison meteorite fell in Australia in 1969 and has been a "benchmark" sample for studying organic molecules in carbonaceous meteorites. The comparison shows that there are sharp differences between the two: the amino acid isotope signature in the Murchison meteorite shows that they are more likely to have formed in an environment with liquid water and relatively mild temperatures. Such conditions may exist on the meteorite parent body and are similar to the environment on the early Earth.
McIntosh points out that amino acids are crucial because science generally agrees that they played a central role in the origin of life on Earth. This study found that the isotope patterns of amino acids in the "Bennu" sample are completely different from those in the Murchison meteorite, indicating that their parent objects were likely born in regions of the solar system with vastly different chemical environments. This further strengthens the idea that there were a variety of different chemical "ecological niches" inside the early solar system, providing a diverse stage for the generation of raw materials for life.
The research also throws up new puzzles. Amino acid molecules usually exist in two "chiral" forms that are mirror images of each other, similar to the human left and right hands. It was thought that the two mirror image molecules would show isotopically similar characteristics. However, in this analysis, there was a significant difference in the nitrogen isotope composition of the left and right chiral forms of an amino acid called glutamic acid in the "Bennu" sample. Why do molecules that are chemically almost identical, mirror images only in spatial configuration, leave such different isotopic "signatures"? There is currently no answer to this question.
Scientists believe that understanding the reasons behind this difference may open a new window for us to understand the generation and evolution of life building blocks throughout the solar system. Bachinsky admitted that there are currently "more questions than answers" and the team plans to continue to analyze more meteorite samples from different sources to test whether their amino acids show differences similar to those of Murchison and "Bennu", or whether they will show more diverse formation pathways and environments.
This research was funded by multiple programs including NASA's New Frontiers Program (which funded the OSIRIS-REx mission), and was funded by related scientific research cooperation projects at NASA's Goddard Space Flight Center and the CRESST II Partnership Program. Collaborators also include scientists from NASA's Goddard Solar System Exploration Division, as well as researchers from Rowan University, the American Museum of Natural History, and the University of Arizona's Lunar and Planetary Laboratory, including OSIRIS-REx principal investigator Dante S. Lauretta.
Overall, what the "Bennu" dust samples reveal is a more "tolerant" universe than imagined: deep in the cold and radiation-filled space far away from the star, the building blocks of life can also be quietly formed. This understanding not only expands humankind's imagination of the possibility of extraterrestrial life, but also adds a new perspective to the fundamental question of "where do we come from?"