New research suggests Saturn’s largest moon contains slushy ice layers rather than a vast liquid sea, according to NASA.
It calls into question a decade-old theory about a hidden ocean beneath the surface of Saturn’s moon Titan.
Instead of a vast underground ocean, Titan may contain deep layers of ice and slush similar to Arctic sea ice or aquifers, according to a study published on Wednesday in the journal Nature. The finding suggests pockets of liquid water could exist within these layers—environments where life might potentially survive.
Researchers at NASA’s Jet Propulsion Laboratory reexamined data collected years ago by the Cassini spacecraft and reached conclusions that contradict the widely accepted ocean theory.
“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 who co-authored the study.
Journaux noted that any life forms would likely be microscopic, adding that “nature has repeatedly demonstrated far greater creativity than the most imaginative scientists”.
No signs of life have been detected on Titan, which spans 3,200 miles and ranks as the solar system’s second-largest moon. Shrouded by a hazy atmosphere, Titan is the only world apart from Earth known to have liquid on its surface, though at temperatures around -297 degrees Fahrenheit, that liquid is methane, not water, forming lakes and falling as rain.
While the absence of a full ocean might seem like a setback for the search for life, researchers say it actually broadens the possibilities. “It expands the range of environments we might consider habitable,” said Ula Jones, a UW graduate student in Journaux’s lab who worked on the study.
The researchers found that pockets of freshwater on Titan could reach temperatures of 21 degrees Celsius.
Nutrients would be more concentrated in these small water pools, potentially creating richer conditions for life than a diluted ocean would provide. If life exists on Titan, it may resemble polar ecosystems on Earth.
A Dynamic Interior
Lead author Flavio Petricca, a postdoctoral fellow at JPL, said Titan’s subsurface water may have frozen in the past and could now be melting, or the moon’s hydrosphere might be gradually freezing solid.
Computer models indicate these ice, slush and water layers extend more than 340 miles deep. An outer ice shell about 100 miles thick covers layers of slush and water pools that reach down another 250 miles.
The breakthrough came from improved analysis of how Saturn’s gravity affects Titan. Because Titan is tidally locked to Saturn—always showing the same face to the planet—Saturn’s gravitational pull deforms the moon’s surface, creating bulges up to 30 feet high.
In 2008, scientists first proposed that Titan must possess a huge ocean beneath the surface to allow such significant deformation. But the new study introduces a crucial detail: timing.
Petricca’s team measured a 15-hour delay between the peak gravitational pull and the rise of Titan’s surface. Like a spoon stirring honey, it takes more energy to move a thick, viscous substance than liquid water. A liquid ocean would respond immediately, Petricca explained, but the delay indicates a slushy ice interior with liquid water pockets.
“Nobody was expecting very strong energy dissipation inside Titan. That was the smoking gun indicating that Titan’s interior is different from what was inferred from previous analyses,” Petricca said.
Journaux’s planetary cryo-mineral physics laboratory at UW helped ground the results by simulating the extreme pressures found deep inside Titan.
“The watery layer on Titan is so thick, the pressure is so immense, that the physics of water changes. Water and ice behave in a different way than seawater here on Earth,” he said.
Skepticism Remains
Sapienza University of Rome’s Luciano Iess, whose previous studies using Cassini data indicated a hidden ocean at Titan, is not convinced by the latest findings.
While “certainly intriguing and will stimulate renewed discussion … at present, the available evidence looks certainly not sufficient to exclude Titan from the family of ocean worlds,” Iess said in an email to AP.
NASA’s planned Dragonfly mission — featuring a helicopter-type craft due to launch to Titan later this decade — is expected to provide more clarity on the moon’s innards. Journaux is part of that team.
The mission should arrive at Titan in 2034, becoming the second flying vehicle on another world besides Earth, after Ingenuity, the Mars helicopter. Dragonfly’s surface observations are hoped to reveal more about where life may be lurking and how much water might be available for organisms. Journaux is part of that mission team.
Titan joins other moons suspected of harbouring water beneath their surfaces. Jupiter’s moon Ganymede is slightly larger than Titan and may have an underground ocean. Saturn’s Enceladus and Jupiter’s Europa are also believed to be water worlds, with geysers erupting from their frozen crusts.
Saturn has 274 known moons, the most in the solar system.
The Cassini mission began in 1997 and lasted nearly 20 years, orbiting the ringed planet and studying its moons before intentionally diving into Saturn’s atmosphere in 2017.