Researchers using archival data from the ALMA (Atacama Large Millimeter/submillimeter Array) have found evidence that molecules of vinyl cyanide, also known as acrylonitrile, are present on Saturn’s hazy moon Titan. Under the right conditions, like those found on Titan’s surface, vinyl cyanide may naturally coalesce into microscopic spheres resembling cell membranes.
Titan is shown in an optical-infrared (atmosphere-surface) composite from NASA’s Cassini spacecraft. In a liquid methane environment, vinyl cyanide may form membranes. Image credit: B. Saxton / NRAO / AUI / NSF / NASA.
Titan is one of the most intriguing planetary bodies in the Solar System.
It is nearly as large as Mars and has a hazy atmosphere made up mostly of nitrogen with a smattering of organic, carbon-based molecules, including methane and ethane.
Planetary researchers theorize that this chemical make-up is similar to Earth’s primordial atmosphere.
The conditions on Titan, however, are not conducive to the formation of life as we know it; it’s simply too cold.
At 10 times the distance from the Earth to the Sun, Titan is so cold that liquid methane rains onto its solid icy surface, forming rivers, lakes, and seas.
In 2015, Cornell University researchers tackled the question of whether any organic molecules likely to be on Titan could, under such inhospitable conditions, form structures similar to the lipid bilayers of living cells on Earth.
Thin and flexible, the lipid bilayer is the main component of the cell membrane, which separates the inside of a cell from the outside world.
Those scientists identified vinyl cyanide as the best candidate. They proposed that vinyl cyanide molecules could come together as a sheet of material similar to a cell membrane.
The sheet could form a hollow, microscopic sphere that they dubbed an ‘azotosome.’ This sphere could serve as a tiny storage and transport container, much like the spheres that lipid bilayers can form.
Now, a research team led by Dr. Maureen Palmer of NASA’s Goddard Space Flight Center has identified the chemical fingerprint of vinyl cyanide in archival ALMA data.
“The presence of vinyl cyanide in an environment with liquid methane suggests the intriguing possibility of chemical processes that are analogous to those important for life on Earth,” Dr. Palmer said.
“The ability to form a stable membrane to separate the internal environment from the external one is important because it provides a means to contain chemicals long enough to allow them to interact,” said team member Dr. Michael Mumma, director of NASA’s Goddard Center for Astrobiology.
“If membrane-like structures could be formed by vinyl cyanide, it would be an important step on the pathway to life on Titan.”
The researchers determined that vinyl cyanide is plentiful in Titan’s atmosphere, present at concentrations up to 2.8 parts per billion.
The chemical is probably most abundant in the stratosphere, at altitudes of at least 125 miles (200 km).
Eventually, vinyl cyanide makes its way to the cold lower atmosphere, where it condenses and rains out onto the surface.
The team also calculated how much material could be deposited in Ligeia Mare.
“Over the lifetime of Titan, Ligeia Mare could have accumulated enough vinyl cyanide to form about 10 million azotosomes in every milliliter, or quarter-teaspoon, of liquid,” the authors said.
“That’s compared to roughly a million bacteria per milliliter of coastal ocean water on Earth.”
“The detection of this elusive, astrobiologically relevant chemical is exciting for scientists who are eager to determine if life could develop on icy worlds such as Titan,” said team member Dr. Martin Cordiner, also of NASA’s Goddard Space Flight Center.
“This finding adds an important piece to our understanding of the chemical complexity of the Solar System.”
The research is published in the July 28, 2017 issue of the journal Science Advances.
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Maureen Y. Palmer et al. 2017. ALMA detection and astrobiological potential of vinyl cyanide on Titan. Science Advances 3 (7): e1700022; doi: 10.1126/sciadv.1700022
