Mimas, wobbling moon of Saturn, may be hiding an ocean

ITHICA, N.Y., Oct. 16 (UPI) —

Even among news absorbed by astronomy buffs, Saturn’s moon Mimas rarely makes the headlines. Other, more exciting orbs — that shoot water out of fissures or remain shrouded in a thick atmosphere of methane — steal the show.

But as any good high school teacher could have warned these planetary scientists, the quiet ones often harbor the deepest, darkest secrets.

"We thought it was the most boring satellite," Radwan Tajeddine, a planetary scientist at Cornell University, told Science Now. Tajeddine and his colleagues now believe Mimas’ cold, lifeless exterior may be hiding something rather exciting — an ocean. Scientists say a subterranean ocean would explain the moon’s strange, wobbling rotation.

"After carefully examining Mimas, we found it librates — that is, it subtly wobbles — around the moon’s polar axis," Tajeddine explained in a recent press release. "In physical terms, the back-and-forth wobble should produce about 3 kilometers of surface displacement. Instead we observed an unexpected 6 kilometers of surface displacement."

"We’re very excited about this measurement because it may indicate much about the satellite’s insides," Tajeddine added. "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."

The wobble could also be explained by an oblong core — formed in the shape of rugby ball as it accumulated mass and solidified in its earliest days. The authors say if that was the case, however, one side of the planet would be slightly more pointed than the other due to the extra pull of Saturn’s gravity.

There’s another problem: Mimas doesn’t stay warm enough on its own to keep water in liquid form, though the authors suggest tidal friction could be enough to keep a small portion melted.

But William McKinnon, a planetary scientist at Washington University in St. Louis, says such a feature would eventually work itself out, ironing out the gravitational discrepancies over time until there were no more tides, and thus no more liquid water.

"I find it quite implausible," McKinnon told Science Now.

Ultimately, scientists will need more detailed measurements of the moon’s rotational wobble to get to the bottom of things, and such data may not come for another couple of years. But even if Mimas turns out to be as boring as everyone thought, at least it stirred some controversy.