NASA scientists detected the chemical acrylonitrile in the atmosphere of Saturn’s moon Titan. The place has long intrigued scientists investigating the chemical precursors of life.
On Earth, acrylonitrile, also known as vinyl cyanide, is useful in the manufacture of plastics. Under the harsh conditions of Saturn’s largest moon, this chemical is thought to be capable of forming stable, flexible structures similar to cell membranes. Researchers previously suggested that acrylonitrile is an ingredient of Titan’s atmosphere. But, they did not report an unambiguous detection of the chemical in the smorgasbord of organic, or carbon-rich, molecules.
Now, NASA researchers have identified the chemical fingerprint of acrylonitrile in Titan data collected by the ALMA in Chile. The team found large quantities of the chemical on Titan, most likely in the stratosphere.
The cells of Earth’s plants and animals would not hold up well on Titan, where surface temperatures average minus 290 degrees Fahrenheit, and lakes brim with liquid methane.
In 2015, scientists 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 bi-layer is the main component of the cell membrane, which separates the inside of a cell from the outside world. This team identified acrylonitrile as the best candidate.
The Goddard team determined that acrylonitrile 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. Eventually, acrylonitrile makes its way to the cold lower atmosphere, where it condenses and rains out onto the surface.
The researchers calculated how much material could be deposited in Ligeia Mare, Titan’s second-largest lake. Over the lifetime of Titan, the team estimated, Ligeia Mare could have accumulated enough acrylonitrile to form about 10 million azotosomes in every milliliter, or quarter-teaspoon, of liquid. That’s compared to roughly a million bacteria per milliliter of coastal ocean water on Earth.
In the combined data set, researchers identified three spectral lines that match the acrylonitrile fingerprint. This finding comes a decade after other researchers inferred the presence of acrylonitrile from observations made by the mass spectrometer on NASA’s Cassini spacecraft.
The detection of this elusive chemical is exciting for scientists to determine if life could develop on icy worlds. This finding adds an important piece to our understanding of the chemical complexity of the solar system.