It's no secret -- people love Titan. Some of the fascination comes from its somewhat Earth-like qualities, as it's the only body in the Solar System with surface-level lakes, rivers, and seas. However, the planet is also undeniably alien, as the "water" in the those extraterrestrial waterways is made of methane, and because methane is half as dense as water, swimming isn't an option. Any future spacefarer would sink like a rock (if they somehow survived the moon's -180°C surface temperature).

But that doesn't mean that other parts of the moon couldn't be potentially more hospitable to life. A team of astronomers at the University of Hawai'i at Mānoa provided evidence in a study, published in The Planetary Science Journal, that a subterranean ocean could be separated from the surface by a six-mile-thick crust of methane ice. As part of the NASA Cassini Data Analysis Program project, which pores through data gathered from the Cassini-Huygens spacecraft which arrived at Saturn back in 2004, the team discovered that impact craters on Titan's surface were shallower than expected. This realization led the scientists to rethink the famous moon's internal structure.

"This was very surprising because, based on other moons, we expect to see many more impact craters on the surface and craters that are much deeper than what we observe on Titan," says Research Associate Lauren Schurmeier, a co-author of the study, said in a press statement. "We realized something unique to Titan must be making them become shallower and disappear relatively quickly."

To figure out exactly what was going on, the researchers computer-modeled the planet's possible topography and concluded that the moon's ice shell could be insulated by a three-to-six-mile-thick layer of methane clathrate ice, which is simply a kind of solid water ice with methane gas dispersed through its crystalline structure. Because the authors were unsure of the craters' initial size, they compared impact sites with Jupiter's similarly-sized icy moon Ganymede, and the results showed a surprise side-effect of this icy crust.

"The methane clathrate crust warms Titan's interior and causes surprisingly rapid topographic relaxation, which results in crater shallowing at a rate that is close to that of fast-moving warm glaciers on Earth," Schumeier says.

The researchers note that studying Titan's methane crust, and how it impacts its hydrological cycle, could help scientists understand how methane can impact Earth's climate back home, especially as methane clathrates continue to seep from the permafrost in Siberia. Of course, a warming effect with an ocean far below the surface is a surprisingly similar condition to that of Europa, and NASA just launched a mission to this Jovian moon in search of life beneath its icy surface. So it makes sense that NASA already has a mission, called the Dragonfly mission, to go check out this methane-filled world with a rotorcraft.

"If life exists in Titan's ocean under the thick ice shell," Schurmeier says in a press statement, "any signs of life (biomarkers) would need to be transported up Titan's ice shell to where we could more easily access or view them with future missions. This is more likely to occur if Titan's ice shell is warm and convecting."

We'll find out when Dragonfly arrives at Titan in 2034. Mark your calendars.