Scientists studying material from the asteroid Bennu have uncovered new clues about how some of life’s most basic ingredients may have formed long before Earth existed.
The findings suggest that amino acids—the molecules needed to build proteins—may have originated in extremely cold, radioactive environments in space, rather than only in warm, watery conditions as previously believed.
Amino acids were identified in samples collected from Bennu, a 4.6-billion-year-old asteroid, and delivered to Earth in 2023 by NASA’s OSIRIS-REx mission.
While scientists have known for years that amino acids exist in asteroids and meteorites, how they formed has remained an open question.
New research led by scientists at Penn State and published in the Proceedings of the National Academy of Sciences offers a surprising answer.
The team found evidence that some of Bennu’s amino acids likely formed in frozen ice exposed to radiation in the outer regions of the early solar system, rather than in liquid water.
“Our results really change how we think about where and how amino acids can form,” said study co-leader Allison Baczynski, an assistant research professor of geosciences at Penn State.
She explained that the findings show there are many possible chemical pathways for forming these molecules, even in harsh, icy environments.
The researchers focused on glycine, the simplest amino acid and one of the most basic building blocks of life. Glycine is important because it can form under many conditions and is often used as a marker of early chemical processes that may have led to life.
Its presence in asteroids supports the idea that key ingredients for life were created in space and later delivered to Earth.
To study Bennu’s glycine, the team analyzed a tiny amount of asteroid material—less than a teaspoon—using highly specialized instruments capable of measuring isotopes, small differences in atomic mass that act like chemical fingerprints.
These measurements revealed patterns that do not match the traditional model of amino acid formation, known as Strecker synthesis, which requires liquid water and moderate temperatures.
To better understand the results, the scientists compared Bennu’s amino acids with those found in the famous Murchison meteorite, which fell in Australia in 1969. Amino acids in Murchison appear to have formed in warmer, water-rich environments, possibly similar to early Earth. Bennu’s samples, however, showed very different isotopic signatures, suggesting the two space rocks formed in chemically distinct regions of the solar system.
The findings also raise new puzzles. Some amino acids exist in mirror-image forms, like left and right hands. In Bennu, two mirror versions of the same amino acid showed unexpectedly different chemical signatures, something scientists did not anticipate.
“These results give us more questions than answers,” Baczynski said. “But that’s exciting. It tells us that the chemistry behind life’s origins is more diverse than we imagined.”
As researchers continue to study Bennu and other meteorites, they hope to build a clearer picture of how life’s building blocks formed—and how common those processes might be throughout the universe.
