Saturn's Titan Has Rigid, Weathered Ice Shell and Strange Interior

Scientists have gotten a new glimpse at Saturn's largest moon, Titan. New data has revealed unexpected features of the moon's outer ice shell, showing that the moon's shell is rigid and that large roots may extend into the underlying ocean.

The gravity and topography data from Saturn's largest moon puzzled scientists when they first analyzed it. Collected by NASA's Cassini spacecraft, the data showed that there was a negative correlation between the gravity and topography signals on Titan.

"Normally if you fly over a mountain, you expect to see an increase in gravity due to the extra mass of the mountain," said Francis Nimmo, one of the researchers, in a news release. "On Titan, when you fly over a mountain the gravity gets lower. That's a very odd observation."

In order to explain this strange occurrence, the researchers developed a model in which each bump in the topography on the surface of Titan is offset by a deeper "root" big enough to overwhelm the gravitational effect of the bump on the surface. The root is like an iceberg below the surface of Titan, extending beneath the hard ice shell into the ocean.

Ice has a lower density than water, so there's less gravity when you have a large chunk of ice than when you just have water. An iceberg floating in water is in equilibrium with its buoyancy balancing out its weight. In the model of Titan, though, the roots extend below the ice sheet and are much bigger than the bumps on the surface. This means that their buoyancy is pushing them up against the ice sheet.

"It's like a big beach ball under the ice sheet pushing up on it, and the only way to keep it submerged is if the ice sheet is strong," said Douglas Hemingway, one of the researchers, in a news release. "If large roots are the reason for the negative correlation, it means that Titan's ice shell must have a very thick rigid layer."

The findings reveal a little bit more about Titan. More specifically, it shows that the moon's ice shell isn't being recycled like Earth's crust. Instead, the ice shell is being shaped by erosion and weather. This finding in particular tells scientists a little bit more about the formation of this moon.

The findings are published in the journal Nature.