Titan's interior: Too cold to form layers

Space agency scientists said the subtle gravitational tugs they measured during Cassini's recent fly-bys of Titan shows the moon evolved in a different fashion from inner planets such as Earth, or icy moons such as Jupiter's Ganymede, whose interiors have split into distinctive layers.

"These results are fundamental to understanding the history of moons of the outer solar system," said Cassini Project Scientist Bob Pappalardo at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We can now better understand Titan's place among the range of icy satellites in our solar system."

The researchers said Cassini's measurements help construct a gravity map, which may help explain why Titan has a stunted topography, since interior ice must be warm enough to flow slowly in response to the weight of heavy geologic structures, such as mountains.

"The ripples of Titan's gravity gently push and pull Cassini along its orbit as it passes by the moon and all these changes were accurately recorded by … the Deep Space Network within 5 thousandths of a millimeter per second even as the spacecraft was more than 600 million miles away," said Luciano Iess, a Cassini science team member at Sapienza University in Rome, and the study's lead author. "It was a tricky experiment."

The research appears in the journal Science.

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