Formation of Complex Organic Compounds through Carbon Atom Diffusion on Interstellar Ice Grains

Laboratory-based investigations have unveiled the intricate process by which carbon atoms disperse across the surfaces of interstellar ice grains, leading to the formation of complex organic compounds. This revelation holds immense significance in elucidating the chemical intricacies of the cosmos. Unraveling the realm of carbon-based chemistry in interstellar space is pivotal for comprehending the broader universe’s chemistry, the genesis of life on Earth, and the potential for life elsewhere.

The catalog of organic molecules detected in space, along with our understanding of their interactions, continues to expand steadily, thanks to ever-improving direct observations. Nevertheless, laboratory experiments dissecting these intricate processes provide equally significant insights. Researchers hailing from Hokkaido University, in collaboration with their counterparts at The University of Tokyo, Japan, have published novel insights into the pivotal role of carbon atoms on interstellar ice grains in the esteemed journal Nature Astronomy.

Formation on the icy grains of space:
Some of the most complex organic molecules found in space are believed to originate on the surfaces of interstellar ice grains, which exist at extremely low temperatures. Ice grains, amenable to this process, are known to be widespread throughout the universe.

All organic molecules share a foundational structure of interconnected carbon atoms. Initially, most carbon atoms were forged through nuclear fusion within stars, later dispersed into interstellar space upon these stars’ demise in supernova explosions. However, the formation of intricate organic molecules demands a mechanism that brings carbon atoms together on the surfaces of ice grains, facilitating encounters with partner atoms and the establishment of chemical bonds. The recent research proposes a feasible mechanism for this intricate process.

Diffusion and reactions on the icy grains:
“In our investigations, simulating plausible interstellar conditions within the laboratory, we have detected the migration of loosely bound carbon atoms across the surfaces of ice grains, culminating in the creation of C2 molecules,” states chemist Masashi Tsuge, affiliated with Hokkaido University’s Institute of Low Temperature Science. C2, also recognized as diatomic carbon, comprises a pairing of two carbon atoms; its formation stands as tangible evidence of carbon atom diffusion on interstellar ice grains.

The research has unveiled that such diffusion could transpire at temperatures exceeding 30 Kelvin (equivalent to minus 243 °C/minus 405.4 °F), while in space, carbon atom diffusion could commence at merely 22 Kelvin (equivalent to minus 251 °C/minus 419.8 °F).

Implications and a broader perspective:
Tsuge asserts that these findings introduce a previously overlooked chemical process into the equation, elucidating how more intricate organic molecules might evolve through the gradual incorporation of carbon atoms. These processes could potentially take place within protoplanetary disks encircling stars, ultimately contributing to planet formation. Furthermore, the requisite conditions can manifest in what are termed translucent clouds, which ultimately evolve into star-forming regions. This could also account for the genesis of the chemicals that might have seeded life on Earth.

Beyond the question of life’s origins, this research introduces a fundamental new process to the array of chemical reactions that could have given rise to, and continue to contribute to, carbon-based chemistry across the cosmos.

The authors also provide an overview of the current understanding of complex organic chemical formation in space and contemplate how reactions driven by diffusing carbon atoms might alter the existing framework.

Reference: “Surface diffusion of carbon atoms as a driver of interstellar organic chemistry” by Masashi Tsuge, Germán Molpeceres, Yuri Aikawa, and Naoki Watanabe, published on 14 September 2023 in Nature Astronomy, DOI: 10.1038/s41550-023-02071-0.

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