Laboratory studies have revealed how carbon atoms diffuse across the surface of interstellar ice grains to form complex organic compounds, which are essential for revealing the chemical complexity of the universe.
The discovery of organic (carbon-based) chemistry in interstellar space is crucial to understanding the chemistry of the universe, as well as the origin of life on Earth and the possibilities for life elsewhere.
The list of organic molecules discovered in space and the understanding of how they interact continues to expand thanks to increasingly better direct observations. But laboratory experiments that reveal complex processes can also provide important clues.
Researchers from Hokkaido University, together with colleagues from the University of Tokyo (Japan), publish in the journal Nature Astronomy a new laboratory study on the central role of carbon atoms in interstellar ice grains.
Some of the most complex organic molecules in space are thought to be produced on the surface of interstellar ice grains at very low temperatures. It is known that ice grains suitable for this purpose are abundant throughout the universe.
All organic molecules rely on a skeleton of bonded carbon atoms. Most carbon atoms were originally formed through nuclear fusion reactions in stars, and eventually spread into interstellar space when stars died in supernova explosions.
But to form complex organic molecules, carbon atoms need a mechanism that allows them to assemble on the surface of ice grains to find partner atoms and form chemical bonds with them. The new research suggests a possible mechanism.
“In our studies, which aim to recreate the conditions possible between stars in the laboratory, we were able to detect weakly bonded carbon atoms that diffuse across the surface of ice grains to react and produce C2 molecules,” explains chemist Masashi Tsuji, from the Low Temperature Institute. Science at Hokkaido University.
C2, also known as diatomic carbon, is a molecule in which two carbon atoms are bonded together. Its composition is tangible evidence of the presence of carbon atoms scattered in interstellar ice grains.
The research revealed that diffusion can occur at temperatures above 30 Kelvin (minus 243 degrees Celsius), while in space, diffusion of carbon atoms can be activated at only 22 Kelvin (minus 251 degrees Celsius).
Tsuji says these discoveries explain how more complex organic molecules can be built by constantly adding carbon atoms.
It suggests that these processes can occur in protoplanetary disks around stars, from which planets are formed. The desired conditions can also form in so-called transparent clouds, which will eventually develop into a star-forming region. This could also explain the origin of chemicals that could have seeded life on Earth.
In addition to the question of the origin of life, the work adds a new fundamental process to the variety of chemical reactions that could have built, and continue to build, carbon-based chemistry throughout the universe.
The authors also summarize the broader current understanding of the formation of complex organic chemicals in space, and explore how reactions driven by the diffusion of carbon atoms could change the current picture.