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Is Saturn’s "Death Star" Moon A Hidden Water World?

Earth’s moon may appear to be a dead, dry, dusty rock in orbit, but the moons of our solar system’s giant planets seem to get more fascinating with each passing year. Scientists’ latest hypothesis is that Saturn’s moon Mimas — which is almost a dead ringer for a real-life natural Death Star replica — may be harboring a hidden interior ocean beneath a thick shell of ice.

This surprising notion was published this week in the journal Science by Radwan Tajeddine, a planetary scientist at Cornell University, and his colleagues who used pictures of Mimas taken by the Cassini spacecraft to create a 3-D model of the moon, which appears on the surface to be just as dry, dead and boring — at least when compared to its intriguing nearby fellow satellites like Titan, Europa or Enceladus — as our own moon. The team found through their modeling that Mimas rotates with quite a bit more of a wobble than was expected for an object that is a nearly perfect sphere. 

“The data suggest that something is not right, so to speak, inside Mimas,” said Tajeddine in a NASA statement. “The amount of wobble we measured is double what was predicted.”

The study investigated the likelihood of two possible explanations: Either the moon has an oblong frozen core, or its frigid crust conceals a liquid water ocean. A number of other moons circling Jupiter and Saturn are believed to hold liquid oceans and be some of the best candidates to host life outside Earth in our solar system, but Mimas has not been among them until now.

Mimas (Credit:NASA)

Other scientists continue to doubt the likelihood of the hidden ocean theory given the lack of geologic activity or other evidence to support such an idea on the surface of the satellite. The authors also concede that the oblong core explanation is not quite consistent with the observed shape of Mimas. They say that further observations by Cassini may help explain the moon’s strange wobble more conclusively.

Some have already suggested competing explanations not considered in the study, like the possibility that Mimas’ strange wobble my be the result of a direct hit by a comet.

Cassini’s next close pass by Mimas will take place in 2016 and could provide another opportunity to gather more data.

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