A new examination of spacecraft data collected more than ten years ago suggests that Saturn's largest moon, Titan, probably does not contain a massive ocean beneath its frozen surface, as scientists once believed. Instead, moving downward through Titan's icy shell would likely reveal additional layers of ice that gradually transition into slushy pathways and isolated pockets of liquid water closer to the moon's rocky interior.

Earlier interpretations of data from NASA's Cassini mission to Saturn led scientists to propose a deep ocean of liquid water hidden beneath Titan's ice. When researchers tested that idea using computer models, however, the results did not align with the physical characteristics seen in the data. A closer reanalysis produced new -- slushier -- conclusions. These results may prompt scientists to revisit assumptions about other icy worlds and refine how they search for life on Titan.

"Instead of an open ocean like we have here on Earth, we're probably looking at something more like Arctic sea ice or aquifers, which has implications for what type of life we might find, but also the availability of nutrients, energy and so on," said Baptiste Journaux, a University of Washington assistant professor of Earth and space sciences.

The study, published Dec. 17 in Nature, was led by NASA, with contributions from Journaux and Ula Jones, a UW graduate student of Earth and space sciences in his lab.

Cassini's Legacy and Titan's Unusual Surface

The Cassini mission began in 1997 and continued for nearly two decades, gathering extensive information about Saturn and its 274 moons. Titan -- shrouded by a hazy atmosphere -- stands out as the only place besides Earth where liquid is known to exist on the surface. With temperatures near -297 degrees Fahrenheit, that liquid is methane, not water. Methane forms lakes on Titan and even falls from the sky as rain.

As Titan travels around Saturn in an elongated orbit, scientists noticed that the moon stretches and compresses depending on its position relative to the planet. In 2008, researchers argued that this pronounced flexing could only occur if a large ocean existed beneath Titan's crust.

"The degree of deformation depends on Titan's interior structure. A deep ocean would permit the crust to flex more under Saturn's gravitational pull, but if Titan were entirely frozen, it wouldn't deform as much," Journaux said. "The deformation we detected during the initial analysis of the Cassini mission data could have been compatible with a global ocean, but now we know that isn't the full story."

A Subtle Time Lag Reveals a Slushy Interior

The new research adds an important factor that earlier studies did not fully consider: timing. Titan's changes in shape lag roughly 15 hours behind the strongest pull from Saturn's gravity. Moving a thick, sticky material requires more energy than shifting a free flowing liquid, similar to how stirring honey takes more effort than stirring water. By measuring this delay, scientists could estimate how much energy Titan absorbs as it deforms, offering insight into how thick or viscous its interior must be.