Titan’s methane lakes revealed by Cassini

The evolution of hydrocarbon lakes on Saturn’s moon Titan is reported in two separate papers published online this week in Nature Astronomy. The studies suggest that some hydrocarbon lakes on Titan are more than 100 metres deep and have been fed by methane rainfall over thousands of years. Others are millimetre-deep ponds that can dry up in one season.

Titan is the only Solar System body beyond Earth where liquid matter can be stable on its surface. Due to the low temperatures that average -180 °C during the day, Titan’s lakes and seas are made up of hydrocarbons and not water. Similar to Earth’s water cycle, a full methane ‘hydrological cycle’ on Titan connects the atmosphere, the surface and the subsurface.

In one paper, Shannon MacKenzie and colleagues use radar and spectral data from NASA’s Cassini spacecraft to identify three features in the northern ‘lake district’, which appear as liquid bodies during Titan’s winter but as land in spring. The authors conclude that such ‘phantom lakes’ were shallow ponds that evaporated or drained into the ground during Titan’s seven-year transition from winter to spring. In a separate study, Marco Mastrogiuseppe and co-authors use radar data from the last Cassini flyby to observe lakes that can exceed a depth of 100 metres. The authors suggest the lakes were created thousands of years ago by methane rain dissolving soluble rocks at the surface. They also find methane drains into the ground at a slower pace than the refill of the lakes by rain, which prevents the lakes from drying up.

Both studies unveil the dynamic nature of the lakes of Titan and its related hydrological cycle, which, much like on Earth, can involve changes from seasonal to epochal.