Using the data archive from the Cassini mission to Saturn, scientists now think that the liquids in Titan’s lakes can stratify into different density layers.

Lakes on Saturn’s moon Titan, composed of methane, ethane, and nitrogen rather than water, experience density driven stratification, forming layers similar to lakes on Earth. However, whereas lakes on Earth stratify in response to temperature, Titan’s lakes stratify solely due to the strange chemical interactions between its surface liquids and atmosphere, says a paper by Planetary Science Institute Research Scientist Jordan Steckloff.

Stratification occurs when different parts of a lake have different densities, with the less dense layer floating atop the denser layer. On Earth, lakes in temperate climates often stratify into layers in the summer as the Sun heats the surface of the lake, causing this water to expand and become less dense, forming a layer of warm water that literally floats upon the cooler water below. This density-driven stratification can occur on Titan as well; however it happens due to the amount of atmospheric nitrogen that Titan’s surface liquids can dissolve, rather than the liquids warming up and expanding.

…Because liquid methane is less dense than liquid ethane, it has been long assumed that Titan’s methane would generally float atop its liquid ethane. However, when methane’s affinity for atmospheric nitrogen is accounted for, methane can dissolve sufficient nitrogen at low temperatures to become denser than ethane.

This result has a great deal of uncertainty, mostly because of the relatively small dataset available of Titan. What it really shows is the possibility of this phenomenon. To confirm it will require some in situ measurements.