Between 2014 and 2016, NASA's Cassini spacecraft bent its instruments toward Titan's vast hydrocarbon seas, bouncing radio signals off their surfaces and listening for what came back. What returned was a portrait of almost preternatural stillness — oceans of liquid methane and ethane so calm their surfaces deviate by no more than a few millimetres from perfect flatness — yet at their edges, where rivers meet reservoirs, something more restless stirs. In the tradition of all great explorations, the clearest answers arrive at the frontier of deeper questions: Titan's seas are known, but their ma