Universe Today
We associate complex chemistry with planets or other bodies, where energy and matter interact in dynamic associations. But as science advances, researchers are finding prebiotic chemistry in a wider variety of places, including in space itself. New research shows that some prebiotic chemicals, part of the recipe for life itself, can form in the cold vacuum of space.
Astrochemistry researchers at the University of Hawaii ran lab experiments mimicking the conditions in interstellar gas clouds. They wanted to determine if specific prebiotic molecules involved in metabolism could form in these cold clouds. They discovered that a complete set of complex carboxylic acids formed in the clouds in only a few million years.
The research, "Abiotic origin of the citric acid cycle intermediates," was published in the Proceedings of the National Academy of Sciences. The lead author is Mason Mcanally, from the W. M. Keck Laboratory in Astrochemistry at the University of Hawaii at Mānoa, Honolulu.
The research focuses on chemistry associated with the Krebs Cycle, also called the Citric Acid Cycle. This metabolic pathway in eukaryotes is critical to energy production. Aerobic organisms use it to convert food into energy.
Other research has shown how tiny specks of dust in cold gas clouds act as reaction sites in forming biomolecules. As scientists learn more about this process, they're discovering that these gas clouds host a surprising richness of organic molecules. This work is adding to that understanding.
"The chemistry of cold molecular clouds is remarkably rich in complex organic molecules," the researchers write. "By replicating the conditions of ice-coated nanoparticles in these cold regions of space, laboratory simulation experiments provide compelling evidence on the synthesis of the complete set of organics of the citric acid cycle in interstellar analog ices exposed to ionizing radiation."
According to theory, the chemicals involved in the Krebs Cycle predate life. Scientists have tried to understand the molecular origins of respiration. They could have formed abiotically and then been adopted by early organisms.
This figure from the research provides an overview of the Krebs Cycle in contemporary biochemistry. It shows reactant molecules involved in synthesizing the cycle's molecular components. Carbon (gray), hydrogen (white), and oxygen (red) are critical elements in biology and interstellar ices. When exposed to cosmic rays in the harsh conditions in molecular clouds, they can produce all of the complex organic molecules in the Krebs Cycle. Image Credit: Macanally et al. PNAS 2025.
"The reliance of all contemporary lifeforms on the Krebs cycle points to its adoption by the earliest living organisms on Earth," the authors write in their paper. "If these molecules are required to form the earliest metabolic systems, an abiotic synthesis of these molecules would be the key to setting the stage for the advent of biochemical evolution."
Japan's Hayabusa 2 recently returned samples to Earth from the asteroid Ryugu. The samples contained carboxylic acids linked to the Krebs Cycle, which adds weight to the idea that Krebs Cycle chemicals can form in space.
The JWST has detected simple molecules in interstellar ices, including methane, carbon dioxide, water, and methanol. Exposure to Galactic Cosmic Rays (GCRs) could process these into organic molecules in the Krebs Cycle.
To further test these results and ideas, the researchers simulated the conditions in molecular clouds by freezing gases to near absolute zero and then exposing them to simulated cosmic rays. Then, they slowly warmed them to simulate the energy from stars forming in the clouds. The experiments produced all of the Krebs cycle's organic acids, including mono-, di-, and tricarboxylic acids.
Some of the generated molecules' abundance matches that found on Ryugu, further strengthening the idea that Krebs Cycle molecules can be generated in clouds. These molecules could make their way into newly forming solar systems, where asteroids or comets could deliver them to planets. This may have been what happened on Earth.
"This work shows that the basic ingredients for life's chemistry could have been made in space, long before Earth even formed," said UH Mānoa Department of Chemistry Professor Ralf I. Kaiser. "By simulating these deep space environments right here in Hawaiʻi, UH scientists are helping uncover how life might start not just on Earth, but anywhere in the universe."
"These results illustrate the interconnected nature of astrophysics, chemistry, and biology in the advent of evolution on early Earth and defines the connection between astrobiology and evolutionary biology," the authors write."
"The complex chemistry of these environments sheds light not only on our own evolution but opens the possibility for evolution on other worlds," they conclude.
More:
Press Release: Scientists recreate deep space chemistry linked to first metabolic systems on Earth
Research: Abiotic origin of the citric acid cycle intermediates
