Diffusion of Carbon Atoms on Interstellar Ice Grains Leads to Formation of Intricate Organic Molecules

Credit for artistic illustration of organic compound formation on interstellar ice goes to Masashi Tsuge.

Research conducted in laboratories illuminates the process by which carbon atoms migrate across the surface of ice grains in interstellar space, leading to the synthesis of intricate organic compounds. These insights are essential for unraveling the chemical intricacies of the universe.

Gaining a comprehensive understanding of carbon-based chemistry in interstellar environments is a key factor in comprehending universal chemistry, as well as the origins of terrestrial life and the prospects for extraterrestrial life.

The catalogue of organic molecules discovered in space is continually growing, thanks in part to increasingly refined observational techniques. Complementary to this, experimental work in labs can provide valuable information. A study published in the journal Nature Astronomy by researchers from Hokkaido University, in collaboration with The University of Tokyo, Japan, provides new laboratory-based insights into the critical role that carbon atoms play on the surface of ice grains in interstellar space.

Molecular Formation on Ice Grains

It is postulated that some of the most intricate organic molecules in space are synthesized on the surface of interstellar ice grains at extremely low temperatures. The type of ice grains conducive to this process are believed to be ubiquitously present throughout the cosmos.

The foundation of all organic molecules is a structure of interconnected carbon atoms. These carbon atoms are primarily the result of nuclear fusion reactions within stars and are disseminated into interstellar space upon the stars’ demise via supernova explosions. For complex organic molecules to form, however, there must be a method for these carbon atoms to coalesce on the surface of ice grains, where they can interact with and bond to other atoms. The newly published research posits such a mechanism.

Above a temperature of 30 Kelvin (minus 243 °C/minus 405.4 °F), carbon atoms are observed to move and bond, creating diatomic carbon, denoted as C2. Credit goes to Masashi Tsuge et al., as reported in Nature Astronomy on September 14, 2023.

Carbon Atom Diffusion and Reaction on Interstellar Ice Grains

During experiments that simulated plausible conditions in interstellar space, Masashi Tsuge, a chemist at Hokkaido University’s Institute of Low Temperature Science, reported that weakly-bonded carbon atoms were observed migrating across ice grain surfaces. These atoms subsequently react to form C2 molecules, otherwise known as diatomic carbon, which consists of two bonded carbon atoms. The formation of C2 is definitive proof of the diffusion of carbon atoms on interstellar ice grains.

The study also showed that this diffusion could take place at temperatures above 30 Kelvin (minus 243 °C/minus 405.4 °F). Meanwhile, in the cosmic environment, activation of carbon atom diffusion may occur at a temperature as low as 22 Kelvin (minus 251 °C/minus 419.8 °F).

Implications and Expanded Context

According to Tsuge, these discoveries highlight a previously unconsidered chemical process that could contribute to the assembly of more complex organic molecules through the incremental addition of carbon atoms. He speculates that these processes could take place in protoplanetary disks surrounding stars, where planets eventually form. Similar conditions may also be present in what are referred to as translucent clouds, which could later transform into star-forming regions. This may further elucidate the origins of the chemicals that could have initiated life on Earth.

Beyond addressing the question of life’s origins, the research introduces a novel basic process to the assortment of chemical reactions potentially responsible for constructing and perpetuating carbon-based chemistry throughout the universe.

The paper also provides a generalized current perspective on the formation of intricate organic chemicals in cosmic settings and examines how reactions instigated by diffusing carbon atoms might revise current understanding.

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 September 14, 2023, in Nature Astronomy.
DOI: 10.1038/s41550-023-02071-0

Frequently Asked Questions (FAQs) about Interstellar Organic Chemistry

More about Interstellar Organic Chemistry

• Nature Astronomy Journal
• Hokkaido University’s Institute of Low Temperature Science
• The University of Tokyo
• Diatomic Carbon (C2) – Britannica
• Supernova Explosions – NASA
• Protoplanetary Disks – NASA
• Translucent Clouds – NRAO
• Origins of Life on Earth – NASA
• Universal Chemistry – Space.com
• Carbon-Based Chemistry – Britannica