As time passed, the region would have cooled down considerably and contracted--thus pulling away from its surroundings and forming fractures akin to the cracks that form in mud as it becomes dry--but on a considerably larger scale.
The precise chemical composition of these very alien lakes and seas remained unknown until 2014, when Cassini's radar instrument detected Ligeia Mare, now known to be Titan's second-largest hydrocarbon-filled lake. Ligeia Mare is brimming with an abundance of sloshing methane, and this enormous liquid reservoir is approximately the same size as two of Earth's Great Lakes combined--Lake Michigan and Lake Huron. Many planetary scientists think that the seabed of Ligeia Mare may be blanketed with a thick layer of sludge that is composed of organic-rich compounds.
The team discovered that the Methone's density would be about 300 kilograms per cubic centimeter. That amounts to less than a third of the density of water, making Methone less dense than any other known moon or asteroid in our Solar System!