Saturn's Wobbly Moon Hints at a Secret Sea

Saturn has a good number of exciting moons circling it. Titan by far its most famous, boasting a mysterious sea of methane, and Enceladus is characterized by its baffling geysers of water vapor and ice particles. However, we may now be adding Mimas to that list of intriguing moons. A new study has revealed that the dull-looking moon is literally shaking with a mystery of its own.

Mimas hasn't gotten a lot of attention in the past, even as NASA's Cassini has been whizzing around Saturn for more than 10 years.

"We thought it was the most boring satellite," Radwan Tajeddine, a planetary scientist at Cornell University, even recently admitted to Science Magazine.

However, a closer look at the moon recently revealed that Mimas has a rotational wobble far larger than expected.

"In physical terms, the back-and-forth wobble should produce about three kilometers of surface displacement," he explained in a statement. "Instead we observed an unexpected six kilometers of surface displacement."

Tajeddine argues in a study recently published in the journal Science that something incredibly interesting has to be going on beneath the tiny moon's geologically boring surface; and the only way to find out what's there is to closely watch the wobble.

"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 said.

According to a resulting study using 3-D computer models and Cassini spacecraft data, the scientist and his colleagues determined that Mimas' interior is not uniform. They concluded that these pronounced wobbles could only be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its "dull" shell.

Tajeddine told the American Association for the Advancement of Science that he personally favors the latter of the two theories, as the gravitational tug of Saturn on Mimas' eccentric orbit could produce enough tidal heating to maintain a liquid interior.

That would also put Mimas in the exclusive club of sea-bearing moons that Saturn's Enceladus and Titan, and Jupiter's moons Europa, Ganymede, and Callisto are already in. And that's pretty cool.