Modeling the seasonality of wind-driven hydrocarbon waves in Titan’s polar lake

Titan, the only body in the solar system aside from Earth with standing liquids on its surface, has polar hydrocarbon lakes and seas. As Titan’s atmosphere generates light winds, there should be waves on the surface of these lakes and seas, yet, direct wave observations are scant. We introduce and use PlanetWaves, an open source 4D spectral wave model, to study Titan’s waves and create seasonal maps of wave shape and propagation on Ontario Lacus and Ligeia Mare. Titan’s modeled waves grow up to 30 times larger than terrestrial waves for the same wind speed, are seasonally present and are largest in the spring and summer when winds are strongest. Average daily winds almost never exceed the wave generation threshold of 0.5–0.7 m/s. Average storm winds (∼1.5 m/s) generate waves 15–48 cm in height with a period ranging 6–10.5 s while maximum storm winds (∼4 m/s) generate waves 2.7–3.2 m in height with a period up to 32 s. Titan’s waves become fetch-independent at ∼40 km for average storm winds occurring ∼1% of a Titan year and ∼100 kilometers for maximum storm winds occurring 2-3 times per Titan decade. On Ontario Lacus, storm winds blow nearly parallel to the eastern shore, potentially driving wave modification of the smooth eastern shoreline. On Ligeia Mare, waves rarely propagate toward a hypothesized wave modified shoreline suggesting that another process, such as tectonics, may contribute to a straight shoreline morphology.