Asteroid Bennu Samples Reveal New Clues to the Origins of Life
In 2023, the OSIRIS-REx mission successfully returned samples from Bennu, a 4.6-billion-year-old asteroid, to Earth. Initial analysis of these pristine materials confirmed the presence of amino acids, the essential components required for building proteins and peptides found within DNA. This discovery validated long-held scientific hypotheses suggesting that the fundamental ingredients for life originated beyond our planet. However, the precise mechanisms behind their formation in the cosmos remained an open question.
Recent research, spearheaded by scientists at Penn State University, has shed new light on this enduring mystery. Published in the Proceedings of the National Academy of Sciences, the study proposes that some of these crucial molecules may have formed within icy, radioactive environments present during the Solar System’s earliest stages. This challenges conventional understanding regarding the conditions necessary for amino acid synthesis in early stellar environments.
Investigating the Isotopic Signatures of Life’s Building Blocks
The research team, comprised of experts from institutions including the Catholic University of America, the American Museum of Natural History, and NASA’s Goddard Space Flight Center, employed specialized instrumentation to analyze the asteroid dust. These custom-built tools allowed for precise measurements of subtle variations in isotopic ratios, providing critical data about the molecules’ origins. Allison Baczynski, assistant research professor of geosciences at Penn State, and Ophélie McIntosh, a postdoctoral researcher in the same department, jointly led the investigation.
Specifically, the team concentrated on glycine, the simplest amino acid, yet vital for numerous cellular processes. As Baczynski explained in a Penn State release, “Here at Penn State, we have modified instrumentation that allows us to make isotopic measurements on really low abundances of organic compounds like glycine.” She further emphasized that advancements in technology were crucial to this breakthrough, stating, “Without advances in technology and investment in specialized instrumentation, we would have never made this discovery.”
A Shift in Understanding Amino Acid Formation
Traditionally, the Strecker synthesis – a process involving hydrogen cyanide, ammonia, and aldehydes or ketones in liquid water – was considered the primary pathway for glycine formation. However, the new findings suggest that glycine within the Bennu sample may have originated differently. The data indicates a potential formation process occurring in ice exposed to radiation in the outer Solar System’s early history, rather than requiring liquid water.
Baczynski summarized the implications of this shift, stating, “Our results flip the script on how we have typically thought amino acids formed in asteroids. It now looks like there are many conditions where these building blocks of life can form, not just when there’s warm liquid water. Our analysis showed that there's much more diversity in the pathways and conditions in which these amino acids can be formed.”
Comparing Bennu to the Murchison Meteorite
To further contextualize their findings, the researchers compared the Bennu glycine signatures with those found in the Murchison meteorite, a well-studied space rock that fell in Australia in 1969. The analysis revealed distinct differences. The amino acids in Murchison appear to have formed through the Strecker synthesis, in warmer temperatures and with liquid water present – conditions potentially mirroring those on early Earth.
“One of the reasons why amino acids are so important is because we think that they played a big role in how life started on Earth,” noted McIntosh. “What’s a real surprise is that the amino acids in Bennu show a much different isotopic pattern than those in Murchison, and these results suggest that Bennu and Murchison’s parent bodies likely originated in chemically distinct regions of the solar system.” Furthermore, the team observed differing nitrogen values between the mirror-image forms of glutamic acid within the Bennu sample, a previously unexpected finding that warrants further investigation. Baczynski concluded, “We have more questions now than answers,” and expressed a desire to analyze a wider range of meteorites to explore the diversity of amino acid formation pathways.
