The flushing of Ligeia: Composition variations across Titan's seas in a simple hydrological model

Abstract

We use a simple box model to explore possible differences in the liquid composition of Titan's seas. Major variations in the abundance of involatile ethane, somewhat analogous to salinity in terrestrial waters, arise from the hydrological cycle, which introduces more "fresh" methane rainfall at the highest latitudes in summer. The observed composition of Ligeia Mare, flushed by methane rainfall and exporting its solutes to Kraken via a narrow labyrinth of channels, may have a methane-rich (>~80%) composition, well out of thermodynamic equilibrium with the atmosphere, whereas the basins of Kraken are relatively well mixed and will have an ethane-dominated (~60%) composition. These variations, analogous to Earth's salinity gradient between the Black Sea and the Mediterranean, may be detectable with Cassini measurements and are important for future exploration.