Exploring Titan's Dynamic Surface with Evaporites

Evaporites are a unique tool for investigating the history of liquids on a surface. Their specific formation conditions make them tell-tale tracers of liquid level change as well as indicators of composition state of the lake... [ view full abstract ]

Evaporites are a unique tool for investigating the history of liquids on a surface. Their specific formation conditions make them tell-tale tracers of liquid level change as well as indicators of composition state of the lake or sea from which they formed. Titan, Saturn’s largest moon, is the only body in the solar system besides Earth to have lakes and seas on its surface. These seas are made of liquid methane and ethane but are mostly found at the moon’s north pole. Titan’s atmosphere is also similar to Earth’s: in it, methane undergoes the same cyclical process that water does on Earth. Thus, conditions across most of the surface of Titan are suitable for methane to be liquid. In fact, Cassini, in orbit around Saturn, has observed rainfall on Titan in equatorial regions. So the question remains-- why are the lakes at seas almost exclusively at the north pole? If liquid has been elsewhere on the surface, how long ago did it dry out? What factors control which lakes dry out first?

Global circulation models have begun to explore these questions from the dynamics perspective. Our study of Titan’s evaporites informs such models by providing the observational evidence of what Titan’s surface looked like in the past, both where the liquid has been and, potentially, if there have been compositional differences/similarities between different bodies. We conduct our analyses with data from Cassini’s Visible and Infrared Mapping Spectrometer, the only instrument able to distinguish the evaporites on Titan’s surface. A better understanding of the long-term climate is crucial for understanding Titan’s evolution over geological timescales-- the current estimates for the composition of the atmosphere can’t reconcile the rate of loss of methane in the upper atmosphere with that estimated in the volume of surface liquid.

Titan’s dynamic processes look a lot like those of Earth but with different compounds playing the same role. Therefore, studies like ours that investigate the complex interaction between Titan’s atmosphere and surface and how to identify that interaction with remote sensing provides important context for studying any planet with an atmosphere, including our own.