TRANSCRIPT – Are Titan’s Lakes Teeming with Primitive Cells?

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Host: Katy Mersmann, NASA Goddard, Communications

Saturn’s largest moon, Titan, is rich in organic molecules: the carbon-based building blocks of life. It’s also the only place that we know of besides Earth with large lakes on its surface…but those lakes are made from super-chilled methane instead of water. So, with its abundant organics and its oily lakes, could exotic lifeforms be brewing on Titan?

Well, in 2017, NASA scientists discovered that this moon’s atmosphere contains acrylonitrile, an organic molecule that is attracted to both water and oil. Scientists think that such “amphiphile” molecules could cluster together within Titan’s lakes to form hollow, double-layered spheres called “vesicles.” These vesicles strongly resemble cell membranes on Earth, making the discovery of acrylonitrile exciting. But in 2020, a follow-up study determined that vesicles would be unlikely to form on Titan without an additional source of energy, casting doubt on their emergence.

Now, a new study coauthored by NASA shows that the missing spark could come from rainfall. Here’s how the process works: in Titan’s upper atmosphere, methane and molecular nitrogen are broken apart by sunlight and recombine into amphiphiles. Rainfall transports the amphiphiles to a lake, where they form a thin film on the surface. Later, strong storms pelt the lake with large raindrops, throwing up a spray of methane droplets coated in a single layer of amphiphiles. As the droplets fall and sink through the lake’s filmy surface, they receive a second coating – and voila! Vesicles.

If they do exist, Titan’s vesicles would likely have a range of different chemistries, some more stable than others. Over time, the most stable compositions would build up in an evolutionary process that could lead to the formation of simple protocells. What are the odds of actually finding these prebiotic bubbles beneath Titan’s pond scum? While the new study is speculative, it proposes that a future spacecraft could sail across Titan’s lakes scanning for vesicles through laser light scattering. In the meantime, NASA is already planning to hunt for new organics when the Dragonfly mission gets to Titan in 2034.

So, stay tuned for future dispatches from Saturn’s chilly, oily, and weirdly Earthlike moon.

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