‘Death Star’ moon’s secret underground ocean
Scientists have found compelling evidence that Saturn’s ‘Death Star’ moon is hiding an ocean just beneath its surface, furthering the search for possible life in our Solar System. Researchers say Mimas, Saturn’s smallest, innermost moon, whose resemblance to Star Wars’ infamous battle station inspired its nickname, revealed the first clue that it could be a ‘stealth ocean world’ after NASA’s Cassini probe spotted a strange wobble in the moon’s rotation.
Recent research suggests that the wobble could be the result of the sloshing of a liquid ocean trapped just beneath the icy surface of the 395km diameter moon. If this is the case, researchers say that
Mimas is an entirely new type of world. The discovery of the tiny moon’s secret ocean could mean that water, and the possible life it can sustain, could be far more abundant in our Solar System than first thought. “If Mimas has an ocean, it represents a new class of small ‘stealth’ ocean worlds with surfaces that do not betray the ocean’s existence,” said Alyssa Rhoden, a geophysicist at the Southwest Research Institute in San Antonio, Texas.
Interior water ocean worlds, such as Saturn’s Enceladus or Jupiter’s Europa, are not new to scientists, but inner tidal processes tend to fracture their surfaces and they show other signs of geological activity. Mimas, on the other hand, looked at first glance like it was “just a frozen block of ice,” Rhoden said. “Turns out Mimas’ surface was tricking us, and our new understanding has greatly expanded the definition of a potentially habitable world in our Solar System and beyond.”
To investigate the possibility of a hidden ocean under Mimas’ frozen surface, the researchers built a model to see if its gravitational interactions with Saturn could produce the tidal forces necessary to heat the moon’s interior, keeping the water below its 25 to 30km thick ice shell warm enough to remain liquid. “Most of the time when we create models, we have to fine-tune them to produce what we observe,” Rhoden said. “This time evidence for an internal ocean just popped out of the most realistic ice-shell stability scenarios and observed librations [planetary wobbles].” This makes Mimas a compelling target for investigation. By studying the moon’s ability to support an ocean, scientists could glean a better understanding of other potential hidden ocean moons tucked farther out in our Solar System, such as the moons of Uranus.
Ben Turner