Saturn’s Death Star Could Be a ‘Stealth’ Ocean World in Disguise

Saturn’s innermost moon Mimas may be hiding a vast subterranean ocean locked beneath its icy surface, according to the results of a new study.

Mimas is just one of 63 confirmed moons in Saturn’s eclectic family, which come in a dizzying array of shapes and sizes, from the stress-fractured shape of Enceladus to the misshapen mass of Hyperion, which has a significantly lower density than water.

What makes Mimas unique – beyond the fact that it orbits closer to the surface of Saturn’s clouds than any other major moon – is the vast impact scar known as Herschel Crater, which dominates its pockmarked characteristics.

The cyclopean appearance granted by the 80-mile-wide (130 km) wound has led many to dub it Saturn’s Death Star moon, in reference to the iconic Star Wars battlestation.

Now, a new study published in the journal Geophysical Research Letters has found evidence to suggest that Mimas is indeed not a (normal) moon, but rather a stealthy ocean world in disguise.

Near the end of its nearly 20-year mission, instruments aboard NASA’s Cassini spacecraft detected a subtle wobble in Mimas’ natural rotation. This unexpected discovery either suggested that Mimus harbored a strangely elongated rocky core or, more likely, that its icy shell veiled an ocean hidden beneath the surface.

These theories prompted the authors of the new study to take a closer look at the violent impact that shaped Mimas’ Herschel crater to see if they could reconcile this violent event with the presence of an inland ocean.

The team reconstructed their creation using advanced computer modeling software and found that the presence of an underground ocean actually helped explain both the shape and depth of the crater, as well as the absence global surface fractures of the moon.

However, models also showed that Mimas’ icy outer shell had to be at least 34 miles (55 km) thick to survive the impact. Any thinner, and that region of the ice shell would have been obliterated by the incredible energy imparted by the strike.

Given that the current thickness of Mimas’ icy outer shell is estimated to be at most 19 miles (30 km) deep, this discovery suggests that the tiny moon has undergone significant warming since impact, resulting in a decrease in ice thickness.

The team also notes that while their findings support the possibility that an ocean could exist on Mimas, it’s still possible that the moon is entirely frozen over both in the present day and at the point of impact. In this scenario, the strange features of Mimas’ orbit should result from the shape of the moon’s core.

“Mimas seemed like an unlikely candidate, with its icy, heavily cratered surface marked by a giant impact crater that makes the small moon look like Star Wars’ Death Star,” said Dr Alyssa Rhoden of SouthWest Research. Institute, who was one of the authors of the new study.

“If Mimas has an ocean, it represents a new class of small ‘stealth’ ocean worlds with surfaces that don’t betray the existence of the ocean.”

The scientists note that future uncrewed missions to the Saturnian system would be invaluable in unlocking the secrets of Mimas’ evolution, and that the moon “could be the first example of a new pathway to the formation of potentially habitable ocean worlds”. .

Image Credit: NASA/JPL/SSI

Anthony is a freelance contributor covering science and gaming news for IGN. He has over eight years of experience covering groundbreaking developments in multiple scientific fields and has absolutely no time for your shenanigans. Follow him on Twitter @BeardConGamer

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