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Saturn moon Titan’s rigid ice shell suggests strange interior with massive roots

According to a news release from the University of California at Santa Cruz, a careful examination of gravity and topography data from Titan has divulged surprising characteristics of the moon’s outer ice shell. According to the study’s authors, Titan’s ice shell is rigid. And, minute topographic characteristics on the moon’s surface are linked to large roots reaching into the ocean beneath.

According to NASA, Saturn’s largest moon appears like a frozen version of Earth before life started adding oxygen into our atmosphere. Astronomers are fascinated by the moon because it contains an active atmosphere and intricate, Earth-like processes that form its surface.

The research utilized new data from the space agency’s Cassini spacecraft. UC Santa Cruz researchers were stunned to discover 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. On Titan, when you fly over a mountain the gravity gets lower. That’s a very odd observation,” said Francis Nimmo, a professor of Earth and planetary sciences at UC Santa Cruz.

According to the model created by researchers, each bump in the topography on the surface of Titan is counterbalanced by a deeper “root” large enough to defeat the gravitational effect of the bump on the surface. The researchers compared Titan’s root system to an iceberg reaching below into the ocean beneath.

“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 said.

According to the model, the roots reaching below the ice sheet are so much larger than the bumps on the surface that their buoyancy is pressing them up against the ice sheet. The negative correlation between the gravity and topography signals on Titan suggests that Titan’s ice shell must contain an extremely thick rigid layer, according to lead author Douglas Hemingway, a doctoral candidate in planetary geophysics at UC Santa Cruz.

The researchers believe that Titan’s ice shell contains a rigid layer at least 40 kilometers thick.

The results have several meanings. For instance, a thick rigid ice shells means it is extremely hard to create ice volcanoes, which some have suggested to give a reason for certain characteristics observed on the surface. Also, Titan’s ice shell isn’t being recycled by convection or plate tectonics.

The researchers have been unable to pin down an explanation for Titan’s topographical characteristics with their fathomless roots. However, Titan’s bizarre orbit around Saturn produces tides that bend the moon’s surface and generate tidal heating, which could cause differences to form in the thickness of the ice shell.

The study’s findings are described in greater detail in the journal Nature.