New Analysis of Titan Challenges Current Theories Regarding Saturn's Largest Moon

An analysis of gravity and topography data from Titan, Saturn's largest moon, has forced researchers to reevaluate current theories regarding its formation.

Led by planetary scientists Douglas Hemingway and Francis Nimmo of the University of California, Santa Cruz, the study revealed a surprising 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. On Titan, when you fly over a mountain the gravity gets lower," Nimmo said in a statement. "That's a very odd observation."

As way of explanation, the researchers propose that Titan's ice shell is rigid and that relatively small topographic features on the surface are paired with large roots stretching deep into the underlying ocean, offseting any gravitational effect caused by the surface bump.

Nimmo compares the phenomenon to an iceberg. "Because ice is lower density than water, you get less gravity when you have a big chunk of ice there than when you have water," Nimmo explained.

However, unlike icebergs, which float in water in a state of equilibrium, the roots extending below the ice sheet are so much bigger than the surface feature that their buoyancy is pushing them up against the ice sheet, the researchers explain.

"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," Hemingway explained. "If large roots are the reason for the negative correlation, it means that Titan's ice shell must have a very thick rigid layer."

In all, the researchers calculated that, given this model, Titan's ice shell would have to contain a rigid layer at least 40 kilometers thick, in addition to hundreds of meters of surface erosion and deposition.

These results are corroborated by geomorphologists studying the erosion of impact craters and other features on Titan and carry with them several implications, such as rendering volcanoes, which have been proposed in the past to explain certain features spotted on the surface.

The findings have several implications. For example, a thick rigid ice shell makes it very difficult to produce ice volcanoes, which some have proposed to explain certain features seen on the surface.

As to how these topographical features and deep roots were formed, the researchers hypothesize that the moon's eccentric orbit around Saturn as a possible source, explaining that this could give rise to tides that flex the moon's surface and create tidal heating, resulting in variations in the thickness of the ice shell.