Why are Titan’s river deltas missing? Planetary astronomer Franck Marchis taps in for Beth Johnson to chat with Brown University’s Sam Birch and explore a strange and unexpected mystery on Saturn’s largest moon. Using data from NASA’s Cassini mission and advanced computer modeling, Birch’s team reveals that Titan's shorelines defy Earth-like expectations. Despite Titan's known rivers and seas of liquid methane, the team found a surprising absence of deltas—landforms typically formed when rivers deposit sediment at their mouths. This finding challenges existing geological expectations, as deltas are common on Earth where rivers meet larger bodies of water, and suggests that Titan's geological and climatic processes differ significantly. This discovery opens new avenues for research into Titan's sediment transport mechanisms and its potential to preserve signs of past environmental conditions or even life. (Recorded live 29 May 2025.)