Amino acids, the essential building blocks of life, were discovered in samples from asteroid Bennu, returned to Earth in 2023 by NASA’s OSIRIS-REx mission. Bennu formed 4.6 billion years ago, and scientists have long wondered how these protein-forming molecules originated in space. New research led by Penn State suggests they may have formed in extremely cold, radioactive ice early in the solar system’s history.

The study, published Feb. 9 in the Proceedings of the National Academy of Sciences, indicates that some asteroid Bennu amino acids formed differently than expected. Traditionally, scientists believed such molecules required warm liquid water. However, the new findings show they can also form in frozen environments exposed to radiation.

Researchers analyzed a tiny dust sample using specialized instruments to measure isotopes, focusing on glycine, the simplest amino acid. Glycine is especially important because it is common in prebiotic chemistry and helps form proteins responsible for nearly all biological functions.

Previously, glycine was thought to form mainly through Strecker synthesis, a reaction involving hydrogen cyanide, ammonia, and other compounds in liquid water. But Bennu’s glycine shows isotopic signatures suggesting it formed in cold ice rather than warm water.

To understand the difference, scientists compared Bennu’s amino acids with those from the Murchison meteorite, which fell in Australia in 1969. The Murchison samples showed evidence of formation in liquid water and moderate temperatures, conditions similar to early Earth. In contrast, Bennu’s amino acids likely formed in a chemically different region of the solar system.

The findings raise new questions. Amino acids exist in mirror-image forms, but Bennu’s versions show unexpected nitrogen differences between these forms. Scientists hope further studies of meteorites will reveal whether Bennu is unique or part of a wider pattern, helping explain how life’s building blocks formed and reached Earth. These discoveries suggest the origins of life’s ingredients were more complex and widespread than once believed. Future missions and improved instruments may provide clearer answers about this cosmic mystery today now and its earliest beginnings there too.