Titan has molecules that may link together to form membranes resembling those of living organisms on Earth. The presence of acrylonitrile – also known as vinyl cyanide (C2H3CN) – on Saturn's largest moon has been confirmed by an international team using data from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Titan's atmosphere mostly comprises nitrogen and some carbon-based molecules such as methane and ethane. While scientists suggest this chemical composition is similar to Earth's primordial atmosphere, temperatures on the Mars-sized moon average at –179 °C – so cold that lakes, rivers and seas comprise liquid methane.

Hollow spheres

In 2015, scientists at Cornell University in the US predicted these extreme conditions could allow vinyl-cyanide molecules to link together and form sheet structures similar to lipid bilayers found in living cells on Earth – the main component of a cell's membrane. Like the lipid bilayers, the researchers proposed that the sheet structures could form tiny, hollow spheres called "aztosomes", which could act as small storage or transport containers. However, scientists had been unable to definitively confirm the chemical's presence on Titan in among the planet's array of carbon-rich molecules.

Now, using archival data from ALMA, Maureen Palmer of NASA's Goddard Space Flight Center in the US and colleagues have identified that significant quantities of vinyl cyanide are indeed present on Titan. "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," says Palmer.

Astrobiologically relevant

The team suggests that the chemical is probably most abundant in Titan's stratosphere, where it likely rises, cools, condenses and rains onto the surface. This means that the moon's second largest lake, Ligeia Mare, could have 10 million aztosomes in every millilitre of liquid – in comparison, coastal ocean water on Earth contains roughly a million bacteria per millilitre.

"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," says team member Martin Corinder. "This finding adds an important piece to our understanding of the chemical complexity of the solar system."

The study is presented in Science Advances.