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The methane seas on Saturn’s largest moon are remarkably calm, and it might be because of a thin floating layer of organic gunk.

Titan’s thick atmosphere is full of complex organic compounds, which give it a distinct orange colour. Those compounds are constantly snowing down from the sky, coating the surface. Daniel Cordier at the University of Reims Champagne-Ardenne and Nathalie Carrasco at University of Versailles Saint-Quentin in France calculated what this might mean for the moon’s oceans.

They found that some of the sediments might float atop the seas, which are made primarily of liquid methane and ethane. These sediments, made of organic molecules likely including hydrogen cyanide, could form a thin film over the liquid.

Because those hydrocarbons are less dense and viscous than water and Titan’s gravitational pull is weaker than Earth’s, waves created by winds across the liquid’s surface are more easily tamped down, the researchers found.

A film of organic molecules would probably look more like a patch of floating sand than an oil slick, but it might behave similarly, says Shannon MacKenzie at Johns Hopkins University in Maryland. “There have sadly been quite a few oil spills on Earth, and investigations have found that those actually damp waves,” she says.

Even a film just a single molecule thick could have a large effect, says Cordier. “Of course if the deposit is thicker, the wave damping effect will be more important.” The effect would be strongest for ripples with wavelengths of a few centimetres, so it could stop most waves before they get big enough for us to detect.

While for the most part Titan’s seas have no waves taller than a few millimetres, we have spotted light reflecting off of some larger ripples. That means that the snowfall isn’t preventing all of the waves all of the time. Looking for more reflections could help us figure out exactly what’s going on at the surface of Titan’s seas, MacKenzie says.

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