Cell membranes are a crucial building block for life on Earth but for them to exist on Saturn's moon Titan, with its methane lakes and -290° F temperatures (-170° C) and all, they would require a rather different makeup. NASA scientists have now detected a key ingredient they say could form membrane like-structures in Titan's harsh conditions, providing a new clue in the search for life elsewhere in the solar system.
Back in 2015, scientists from Cornell University conducted a study designed to explore how life could come to exist on colder worlds without water. More specifically, they ran computer simulations investigating chemicals that could make up cell-like membranes on Saturn's largest moon Titan.
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On Earth, these thin, but strong and flexible water-based layers enclose the organic matter of every cell. But in worlds where water doesn't exist but methane does, what would these membranes look like? The researchers determined that the most promising candidate was a colorless, poisonous organic compound called acrylonitrile, also known as vinyl cyanide. The researchers said that these could possibly join together in sheets to form hollow spheres they dubbed azotosomes.
"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," says Michael Mumma, director of the Goddard Center for Astrobiology, which is funded by the NASA Astrobiology Institute. "If membrane-like structures could be formed by vinyl cyanide, it would be an important step on the pathway to life on Saturn's moon Titan."
Now, NASA scientists have detected large amounts of vinyl cyanide in Titan's atmosphere using the ALMA telescope array in Chile. Scientists had suspected the presence of the molecule in Titan's atmosphere previously, but by combining 11 high-resolution data sets from the telescope, the NASA team has now identified three spectral lines that match the chemical's fingerprint.
The team says that vinyl cyanide is present in concentrations up to 2.8 parts per billion, and is probably most abundant in the stratosphere at altitudes of at least 125 mi (200 km). From there, it makes its way down to the lower atmosphere and condenses, before raining onto the surface below.
The team ran some calculations on how much vinyl cyanide could find its way down onto Ligeia Mare, TItan's second largest lake that is around the same surface area of Lake Huron and Lake Michigan joined together. Over Titan's lifetime, it estimated that enough vinyl cyanide could have accumulated to create 100 million azotosomes in every milliliter of liquid.
"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 Goddard scientist Martin Cordiner, senior author on the paper. "This finding adds an important piece to our understanding of the chemical complexity of the solar system."
The video below gives an overview of the discovery, while the research was published in the journal Science Advances.