The complex precursors to biological molecules can form spontaneously in interstellar space, according to a lab experiment that opens up new pathways for the origin of life in the universe.
In the presence of ionizing radiation, amino acids — the simplest units of proteins — couple together to form peptide bonds, the first step in the synthesis of more complex biological molecules such as enzymes and cell proteins, according to a new study.
The cocktail of life
Early life evolved from a complex cocktail of prebiotic molecules, including amino acids, basic sugars and RNA. But how these simple starter compounds first formed remains a mystery. One hypothesis proposes that some of these molecules may have originated in outer space and were later delivered to the early Earth through meteorite impacts, said Alfred Hopkinson, lead author of the study and a postdoctoral researcher in the Department of Physics and Astronomy at Aarhus University in Denmark.
Glycine, the simplest amino acid, is one example that has been detected in numerous comet and meteorite samples over the past 50 years, including dust samples taken from the asteroid Bennu during NASA’s recent OSIRIS-REx mission. More complex dipeptide units, which are formed when two amino acids bond by releasing water, have not been identified in these extraterrestrial bodies yet, but the intensely ionizing conditions of interstellar space gives rise to unusual chemistry and could theoretically promote the formation of these larger molecules.
“If amino acids could join in space and get to the next level of complexity [dipeptides], when that’s delivered to a planetary surface, there’s an even more positive starting point to form life,” Hopkinson told Live Science. “It’s a very exciting theory, and we wanted to see, what is the limit of complexity that these molecules could form in space?”
Remaking the universe in a lab
The team, led by Aarhus University astrophysicist Sergio Ioppolo, therefore sought to reproduce the conditions of outer space as closely as possible. Using the HUN-REN Atomki cyclotron facility in Hungary, they bombarded glycine-coated icy crystals with high-energy protons at 20 kelvins (minus 423.67 degrees Fahrenheit, or minus 253.15 degrees Celsius) and 10-9 millibar, in order to simulate the conditions of space as closely as possible. Then, using infrared spectroscopy and mass spectrometry — methods of identifying the types of bonds present and the products’ molecular mass, respectively — the researchers analyzed the products as they formed.
Crucially, though, they used a series of deuterium labels — heavier atoms of hydrogen that produce a different signal during spectroscopic analysis — to track exactly how the glycine molecules were interacting.
Their labeled experiment quickly confirmed their initial hypothesis: The glycine molecules reacted together in the presence of radiation to form a dipeptide called glycylglycine, thus proving that more complex compounds containing peptide bonds could spontaneously form in space.
More chemical surprises
But dipeptides weren’t the only complex organic molecule generated under these conditions. One surprisingly complex signal was tentatively identified as N-formylglycinamide, a subunit of one of the enzymes involved in the production of DNA building blocks and, therefore, another key player in origin-of-life chemistry.
“If you make such a vast array of different types of organic molecules, that could impact the origin of life in ways we hadn’t thought of,” Hopkinson said. “It’s interesting to speak to other researchers — say, RNA world people — and see how that might change their picture of the early Earth.”
Going forward, though, the team is investigating whether this same process occurs for other protein-forming amino acids in the interstellar medium, which would potentially open up the possibility of forming more diverse and complex peptides with contrasting chemical properties.
Hopkinson, A. T., Wilson, A. M., Pitfield, J., Muiña, A. T., Rácz, R., Mifsud, D. V., Herczku, P., Lakatos, G., Sulik, B., Juhász, Z., Biri, S., McCullough, R. W., Mason, N. J., Scavenius, C., Hornekær, L., & Ioppolo, S. (2026). An interstellar energetic and non-aqueous pathway to peptide formation. Nature Astronomy. https://doi.org/10.1038/s41550-025-02765-7
