There's one other place in the solar system where liquid rains, evaporates, and seeps into the surface to create deep lakes: Saturn's moon Titan.
In this alien world, the Earth-like hydrologic cycle does not take place with water, but with liquid methane and ethane. In Titan's ultra-cold environment, these gases behave just like water.
Two new papers published in the journal Nature Astronomy detailed the findings of the concluded Cassini mission, particularly the details on Titan's lakes and their composition.
"Every time we make discoveries on Titan, Titan becomes more and more mysterious," Marco Mastrogiuseppe, lead author and Cassini radar scientist from Caltech, says in a report from NASA. "But these new measurements help give an answer to a few key questions. We can actually now better understand the hydrology of Titan."
Titan's Deep Lakes Atop Mountains
In the first paper, a Mastrogiuseppe-led team reveal the results of their investigations on Titan's lakes. It provides the first confirmation of the depth of these small western lakes with some reaching more than 300 feet, which suggests they formed when ice and solid organics dissolved and collapsed around them.
Prior to the study, the team was already aware that the moon's bigger northern seas are made up of methane. However, they were surprised to find that the smaller southern lakes are also filled with methane. After all, when scientists previously measured the only major lake in the southern hemisphere, it was made up of both methane and ethane equally.
Another strange feature of Titan: one side of the northern hemisphere appeared to be an entirely different world from the other side, at least in terms of hydrology. In the East are massive seas combined with low elevation landforms of canyons and islands, while on the West there are small but deep lakes on top of rolling hills and plateaus.
"It is as if you looked down on the Earth's North Pole and could see that North America had completely different geologic setting for bodies of liquid than Asia does," Jonathan Lunine, a Cassini scientist and coauthor of one of the papers, explains.
Phantom Lakes On The Surface
The second paper tackles what the researchers refer to as transient lakes, where the liquid appears to have significantly decreased over time.
When Cassini first detected these features on the surface, they appeared to be lakes filled with liquid, but when the spacecraft returned, they're all dried up.
Shannon MacKenzie, lead author and planetary scientist at the Johns Hopkins Applied Physics Laboratory, suggests the "phantom lakes" show evidence of seasonal changes in Titan.
These lakes could have been more shallow than other bodies of liquid on the moon, evaporating as the season shifted.
"Titan is the most interesting moon in the solar system," MacKenzie tells Space.com. "I think that gets me some enemies, but I think it's actually true."