Astronomers are trying to get to the bottom of what exactly is happening under the surface of Mimas, the smallest and closest main moon to Saturn.
Using images taken from the Cassini spacecraft, researchers have found that Mimas' rotation and orbit around Saturn makes the moon look as though it is rocking back and forth and oscillating like a pendulum swings, Space.com reports. This is called libration, and the scientists discovered that in one spot on Mimas, the libration was magnified. That made Radwan Tajeddine, a research associate at Cornell University, believe it is caused by an odd interior.
"We're very excited about this measurement because it may indicate much about the satellite's inside," Tajeddine said in a statement. "Nature is essentially allowing us to do the same thing that a child does when she shakes a wrapped gift in hopes of figuring out what's hidden inside."
Tajeddine and other members of his team tested five different models of what the inside of Mimas might look like, and ruled out three possibilities: that Mimas has a uniform interior, a mass under its crater, or an interior with two separate layers. That leaves two models, one where Mimas has an elongated, oval-shaped core, and the other where there is an ocean under the surface.
There is a strong possibility that one of those models is correct, although Tajeddine does not believe there is a subsurface ocean, since so far astronomers have not seen any evidence of liquid water on Mimas. The results were published this week in Science.