I have to give a mention to a story we missed from our home Planetary Science Institute (PSI) about Saturn’s moon Titan and its lakes.
Again, we have to compare what we know here on Earth to what we find elsewhere in space. In this instance, we know that lakes on Earth experience stratification due to changes in the density of the water from temperature processes. The Sun heats the water, which then becomes less dense and rises to the top of the lake as it warms, leaving cooler layers below.
The same density-driven stratification is found on Titan, but the process is completely different. Instead of layering due to temperature, reactions with the atmospheric nitrogen cause the methane in the lakes to become denser than the ethane instead of the usual other way around. And so the methane rises above the ethane. Institute Research Scientist Jordan Steckloff explained: We focused on small, shallow lakes that fill following Titan’s rain events, and found that, if the temperature is low, the evaporation of methane from the surface can drive out dissolved nitrogen, which is heavy, resulting in an ethane-enriched (methane-nitrogen poor) layer floating on top of a methane-rich layer.
I also love this quote from Steckloff: “Earth is the most Titan-like planet known.” It changes the perspective of how we look at our solar system a little.
“Stratification Dynamics of Titan’s Lakes via Methane Evaporation,” Jordan
K. Steckloff et al., 2020 July 14, Planetary Science Journal