Saturn’s moon Titan challenges ocean theory with a thick and slushy interior

Titan s hidden ocean may have been a mirage. Careful reanalysis of data collected more than a decade ago suggests that Saturn s largest moon does not host a vast, global ocean beneath its icy shell, as scientists once believed.

Instead, descending below Titan s frozen surface may lead not to open water, but to thick slush, icy tunnels, and pockets of meltwater closer to its rocky core. The conclusion comes from a fresh look at data from NASA s Cassini mission, which orbited Saturn for nearly 20 years. Earlier interpretations of Cassini measurements pointed to a massive subsurface ocean of liquid water, long considered one of Titan s most promising features for potential life.

But when researchers modeled Titan with a deep ocean, the numbers no longer added up. The physical properties inferred from the data didn t align with what a global ocean should produce. Reexamining the same measurements with new techniques revealed a very different picture, one that is colder, thicker, and far slushier. The findings not only reshape what scientists think lies beneath Titan s crust but could also influence how researchers assess other icy worlds across the solar system in the search for life.

Ocean myth reexamined Instead of an open ocean like we have here on Earth, we re probably looking at something more like Arctic sea ice or aquifers, said Baptiste Journaux, a University of Washington assistant professor of Earth and space sciences. Titan is already an unusual world. Shrouded in a hazy atmosphere, it is the only place besides Earth known to have stable liquid on its surface. At temperatures around minus 297 degrees Fahrenheit, that liquid is methane, forming lakes and falling as rain.

The original ocean hypothesis came from how Titan physically deforms as it orbits Saturn. As the moon follows an elliptical path, Saturn s gravity stretches and squeezes it. In 2008, scientists argued that such pronounced deformation required a subsurface ocean to allow the icy crust to flex. The degree of deformation depends on Titan s interior structure, Journaux said.

A deep ocean would permit the crust to flex more under Saturn s gravitational pull. What earlier studies missed, the new research shows, was timing. Titan s shape changes lag about 15 hours behind Saturn s strongest gravitational pull. That delay is critical.

Like stirring honey instead of water, deforming a thicker, more viscous interior requires more energy. By measuring how much Titan lags, researchers could estimate how much energy is dissipated inside the moon, and infer what its interior is made of. Slush changes everything Nobody was expecting very strong energy dissipation inside Titan, said Flavio Petricca of NASA s Jet Propulsion Laboratory. That was the smoking gun indicating that Titan s interior is different from what was inferred from previous analyses.

The model that best fits the data replaces a global ocean with a thick slushy layer containing significantly less liquid water. The slush is dense enough to explain the delay but still flexible enough to deform. The implications for life are complex, but not necessarily discouraging. Pockets of freshwater trapped within the ice could reach temperatures as high as 68 degrees Fahrenheit, with nutrients concentrated into smaller volumes.

The discovery of a slushy layer on Titan also has exciting implications for the search for life beyond our solar system, said Ula Jones, a University of Washington graduate student. It expands the range of environments we might consider habitable. The findings will help guide NASA s upcoming Dragonfly mission to Titan, scheduled to launch in 2028, as scientists rethink where and how to look for signs of life.

The study appears in the journal Nature.