Life on Earth emerged from a sequence of chemical steps that remain only partially understood, and the uncertainty surrounding those steps continues to reshape how scientists think about the earliest stages of biology. A new study published in Nature Astronomy provides evidence that a key stage in this sequence can take place in the coldest and most inhospitable environments in the universe. Researchers working across teams in Denmark, the United Kingdom, and Hungary have demonstrated that peptide bonds, which are fundamental to the structure of proteins, can form in interstellar ice analogues exposed to ionizing radiation without any involvement of liquid water. This finding challenges traditional assumptions about the chemical conditions required for life’s precursors and expands the range of environments where biological building blocks may originate. The researchers focused on glycine, the simplest amino acid found in biology and a molecule that has been detected in meteorites and cometary samples returned by space missions. Although glycine has been proposed to form in cold interstellar environments through surface chemistry on dust grains, the subsequent steps needed to convert isolated amino acids into peptides have remained unexplored under conditions that resemble space. Peptides are chains of amino acids joined by peptide bonds. These bonds are essential for the formation of proteins, which in turn support structure, catalysis, replication, membrane formation, and virtually every core biochemical function. The essential role of peptides means that understanding how peptide bonds might arise in nature is a central question in research on the origins of life.
To probe this question, the team conducted laboratory experiments that recreated the physical environment of dense interstellar clouds, which are regions filled with microscopic dust grains coated in layers of frozen molecules. These clouds remain at extremely low temperatures, often around 20 Kelvin, and are exposed to various forms of energetic radiation from cosmic rays and stellar activity. The researchers deposited thin layers of glycine onto infrared transparent substrates cooled to twenty Kelvin. They then irradiated the samples using proton beams with energies that approximated both galactic cosmic rays and solar wind conditions. Throughout the irradiation process, they monitored the samples using infrared spectroscopy to track changes in molecular structures. The researchers found that irradiation triggered the formation of glycylglycine, the simplest dipeptide formed by linking two glycine molecules through a peptide bond. The formation of glycylglycine was confirmed by infrared absorption features corresponding to amide bonds and then validated using high resolution mass spectrometry after the samples were warmed and dissolved. Infrared spectra revealed the presence of amide bands known as amide one, two, and three. These modes arise from specific vibrational patterns in the peptide bond and are different from the vibrational behaviour of isolated glycine molecules. The detection of these bands in the residue left on the substrate indicated that ionizing radiation had converted some fraction of the glycine into peptide bonded structures. Mass spectrometry provided the final confirmation. When the irradiated samples were dissolved and introduced into an electrospray ionization mass spectrometer, molecules with mass to charge ratios consistent with glycylglycine appeared in all irradiated samples. The formation of glycylglycine under these conditions demonstrates that peptide bonds can form in deep space through energetic processes without the presence of liquid water or catalytic surfaces associated with traditional biochemical environments.
One of the striking aspects of this study is the observation that water itself was produced as a byproduct of peptide bond formation. When a peptide bond forms between two amino acids, a molecule of water is released. The researchers used isotopically labelled versions of glycine containing either hydrogen or deuterium to track the production of water during irradiation. Infrared spectroscopy identified clear signatures of H2O, HDO, and D2O that emerged during irradiation, while mass spectrometry during temperature programmed desorption confirmed their release as the samples were warmed. These results indicate that at least some of the water produced in the experiments formed directly as a consequence of peptide bond synthesis. This finding has implications for the interpretation of water in astrophysical environments. Water detected near organic rich ices may partially originate from organic reactions rather than from direct condensation or surface chemistry alone. The isotope tracing experiments also allowed the researchers to distinguish between different mechanisms of water formation. For partially deuterated glycine, water containing hydrogen and deuterium appeared only at higher radiation doses, indicating that some water formed through secondary reactions involving fragments such as carbon dioxide and carbon monoxide. In contrast, fully deuterated glycine produced deuterated water early in the irradiation process, which suggests that peptide bond formation occurred directly between deuterated molecules. By comparing the formation patterns of water isotopologues, the researchers concluded that both direct peptide synthesis and multi step oxidative processes contributed to water production, revealing a chemically rich sequence of reactions initiated by radiation.
The experiments also identified additional complex organic molecules that extend beyond the mass range of glycine. Mass spectra showed numerous peaks up to mass to charge values near 300, indicating a broad array of newly synthesized compounds. Among these, the researchers tentatively identified N formylglycinamide, a molecule that is structurally related to intermediates used in modern metabolic pathways that support purine synthesis. The detection of such species suggests that irradiation can generate a diverse set of amide containing compounds in interstellar conditions. These compounds may play important roles in chemical evolution long before they reach planetary environments.
This study helps bridge an important gap between the formation of amino acids and the appearance of more complex molecules that can support the earliest stages of biochemistry. Previous research established that amino acids can appear in interstellar ices through surface reactions involving radicals and small atoms. Additional studies demonstrated that ultraviolet radiation and energetic particles can produce a variety of organic fragments including carbon monoxide, carbon dioxide, cyanide ions, and more complex carbon bearing species. What has remained difficult to demonstrate is whether these same processes can drive molecular assembly rather than only fragmentation. The new evidence that peptides can form under the same conditions that degrade amino acids indicates that interstellar radiation environments may promote both destruction and synthesis, with the balance depending on energy levels, molecular arrangement, temperature, and exposure duration.
Understanding how peptides form in space is important for several reasons. First, peptides offer catalytic functions. Laboratory studies show that short peptides can accelerate the synthesis of amino acid derivatives and even nucleobase related molecules under some conditions. This means that peptides arriving on a young planet could influence subsequent chemical evolution by lowering reaction barriers or stabilizing molecular structures. Second, peptides can form flexible or ordered structures that contribute to primitive compartment formation. Some peptides self assemble into bilayer or micelle like structures that resemble the compartmentalization functions of protocells. Third, peptides provide a potential link between prebiotic chemistry and the earliest metabolic networks. If peptide bonded molecules originated in interstellar environments, then some of the frameworks underlying early Earth chemistry might have been inherited rather than assembled from scratch on the planet.
The astrophysical implications of peptide synthesis in space are also significant. Dense molecular clouds span vast regions of the galaxy and represent the initial environments in which stars and planetary systems begin to form. If peptide formation occurs on icy grains within these clouds, then the resulting molecules can become embedded within the material that collapses to form protoplanetary disks. From there, they can be incorporated into asteroids, comets, and planetesimals. Comet samples already contain amino acids, suggesting that early Solar System bodies inherited at least some molecular complexity from interstellar chemistry. The addition of peptide bonded molecules to this inventory means that planets like Earth may receive not just simple organics but molecules that are already progressing along pathways associated with biological functionality.
One of the challenges in testing these ideas observationally is the difficulty of detecting glycine and peptides directly in the interstellar medium. Glycine has been tentatively reported in some astronomical observations but remains uncertain because its spectral signatures overlap with other molecules present in star forming regions. Even so, the consistency of laboratory data with the conditions expected in cold interstellar environments strengthens the argument that the building blocks of peptides exist long before planets form. As detection capabilities improve, astronomers may begin to observe molecules that carry amide bonds or related spectral features in dense cloud environments.
The study also highlights the importance of radiation in driving chemical evolution in space. While low temperature environments limit the mobility of molecules on ice surfaces, ionizing radiation can supply energy that breaks bonds, creates radicals, and drives new reactions. The data show that molecular processing is not uniform. Different energy ranges produce different chemical outcomes. Proton energies of ten kilo electronvolts, which resemble solar wind conditions, led to detectable peptide formation. Proton energies of one mega electronvolt, which approximate cosmic ray interactions, produced even more extensive chemical restructuring within the samples. This variety suggests that interstellar grains exposed to mixed radiation fields may undergo a wide range of chemical transformations over time. The cumulative exposure over millions of years could generate a diverse suite of biomolecular precursors even in regions far removed from warm or water rich environments.
These findings reshape how scientists think about abiogenesis by expanding the range of potential environments where meaningful chemistry can occur. Traditional models focus on water based settings such as hydrothermal vents, volcanic pools, or evaporating lagoons on early Earth. These environments allow solutes to interact, concentrate, and assemble into larger structures. However, the new results show that essential chemical steps do not always require liquid water. Instead, they can take place in solid ices subjected to radiation. This expands the possible timeline of prebiotic chemistry by initiating key reactions before planetary surfaces even exist. It also expands the possible spatial locations of early chemistry by including cold interstellar clouds where temperatures prevent liquid water altogether.
The presence of preformed peptides or amide rich molecules in the early Solar System would have influenced the chemical evolution of Earth once these compounds were delivered by meteorites and comets. Entry heating destroys some fraction of organic material, but many molecules survive, as evidenced by the organics still present in carbonaceous chondrites. Once deposited on the surface, peptides may have contributed to early catalytic functions or helped orchestrate additional polymerization. Some researchers suggest that autocatalytic behaviour in peptides can promote self amplification or stabilization of certain molecular structures. If peptides with such properties existed before Earth formed, they may have provided initial directionality to chemical evolution once favorable conditions allowed for further assembly.
The formation of peptides in cold space also raises questions about molecular survivability during transport through interstellar and interplanetary environments. Radiation can both produce and destroy peptides, so the net accumulation depends on exposure duration, shielding, and local chemical composition. Dust grains embedded within dense clouds receive some natural shielding, which might allow peptides to persist long enough to become incorporated into forming solar systems. As these grains collapse into disks and planetesimals, thermal cycling and aqueous alteration may further transform or preserve these molecules depending on the environment. Understanding these processes will require additional laboratory simulations that track peptide stability under varying temperature and radiation conditions.
The results of this study suggest that researchers should consider a broader range of starting materials when modeling early Earth chemistry. Instead of assuming a blank slate of simple molecules delivered to the young planet, researchers may soon need to incorporate a richer set of complex molecules that arrived through inherited extraterrestrial chemistry. This includes peptides, amides, water bearing organics, and other compounds identified in the experiments. The presence of such material could accelerate or redirect the pathways that eventually led to self replicating systems, compartment formation, and metabolism.
Future research will examine how far this type of chemistry can progress under interstellar conditions. The formation of a dipeptide is a fundamental milestone, but it is only an initial step in the broader spectrum of possible molecules. Radiation driven synthesis could potentially lead to longer peptide chains or cross linked structures if molecular mobility and orientation on ice surfaces permit additional bonding. Temperature fluctuations during star formation may also influence reaction yields by increasing diffusion or altering ice structures. By varying radiation intensities, temperatures, and chemical compositions, researchers aim to map the range of possible molecular outcomes in preplanetary environments.
The discovery that peptides can form in interstellar ice under radiation has important implications for our understanding of life’s origins. It suggests that the universe may naturally generate molecules that contribute to biological systems in a wider variety of environments than previously assumed. It also indicates that the initial steps toward biological complexity may occur earlier and more widely than models based solely on planetary chemistry would allow. As analytical techniques improve and astronomical observations become more sensitive, researchers may soon detect direct evidence of amide bearing molecules in space, further strengthening the case that life’s building blocks are widespread.
This study marks a major advance in prebiotic chemistry by demonstrating that peptide formation is not limited to liquid water environments. Instead, it can occur in the deep cold of interstellar space, driven purely by energetic interactions with radiation. The findings broaden the definition of environments where life’s precursors can form and provide a new foundation for theories about how life may begin on planets across the galaxy.
Source:
Hopkinson, A. T. et al. An interstellar energetic and non-aqueous pathway to peptide formation. Nature Astronomy, 2026.
Link: https://doi.org/10.1038/s41550-025-02765-7
