Saturn’s Moon Titan has consistently been one of the most fascinating objects in our solar system. In just the past two years, astronomers have found large bodies of water on the moon, seen the satellite’s weather form a seasonal vortex, and detected hydrocarbon sand on Titan’s surface.

This week, researchers announced that odd gravitational measurements of Titan’s surface taken by the Cassini spacecraft suggest that the moon’s ice shell is rigid. Moreover, bumps in the surface of the shell could indicate large roots of ice that extend deep into the planet’s oceans. This hypothesis was based on the fact that areas of higher topography on Titan’s shell were found to have lower gravity readings, suggesting that they may cover large ice columns that would be less dense than the surrounding water.

“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, a co-author of a paper on the findings published in the journal Nature. “On Titan, when you fly over a mountain, the gravity gets lower. That’s a very odd observation.”

Though the ice column explanation is suitable for Titan’s gravity readings, it could conflict with other observations of the moon. According to NASA, the hypothesis would mean a lack of ice volcanoes, which other researchers have suggested exist on Titan. Also, a fixed ice shell would suggest no plate tectonic action on the moon’s suface.

“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, lead author of the paper and a planetary scientist at the University of California at Santa Cruz. “If large roots under the ice shell are the explanation, this means that Titan’s ice shell must have a very thick rigid layer.”

(Image courtesy ESA/NASA/JPL/University of Arizona)