Samples from asteroid Bennu, returned by NASA's OSIRIS-REx mission in 2023, contain amino acids that likely formed in frozen ice exposed to radiation, according to new research. Penn State scientists analyzed isotopes in the material, challenging traditional views of amino acid origins. The findings, published on February 9, highlight diverse pathways for life's building blocks in the early solar system.
NASA's OSIRIS-REx mission brought back samples from the 4.6 billion-year-old asteroid Bennu in 2023, confirming the presence of amino acids, molecules essential for building proteins and peptides in DNA and central to biological processes.
A study led by researchers at Penn State, published on February 9 in the Proceedings of the National Academy of Sciences, examined a teaspoon-sized portion of Bennu's material using specialized instruments to measure isotopes. The analysis focused on glycine, the simplest amino acid, which serves as a marker for prebiotic chemistry and supports the theory that space-delivered materials contributed to life's origins on Earth.
The isotopic signatures indicate that Bennu's glycine formed under cold, radioactive conditions in the outer regions of the young solar system, rather than through the previously assumed Strecker synthesis in warm liquid water involving hydrogen cyanide, ammonia, and aldehydes or ketones.
"Our results flip the script on how we have typically thought amino acids formed in asteroids," said Allison Baczynski, assistant research professor of geosciences at Penn State and co-lead author. "It now looks like there are many conditions where these building blocks of life can form, not just when there's warm liquid water."
Comparisons with amino acids from the Murchison meteorite, which fell in Australia in 1969 and formed in liquid water at moderate temperatures, revealed differences. "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," said Ophélie McIntosh, postdoctoral researcher in Penn State's Department of Geosciences and co-lead author.
The research also found that the two mirror-image forms of glutamic acid in Bennu's samples have differing nitrogen isotope values, raising new questions. "We have more questions now than answers," Baczynski added. Future analyses of other meteorites aim to explore further diversity in formation pathways.
Co-authors include Mila Matney, Christopher House, and Katherine Freeman from Penn State, along with researchers from NASA's Goddard Space Flight Center, Rowan University, the American Museum of Natural History, and the University of Arizona.