Saturn's Death Star Moon May Be a 'Stealth' Ocean World in Disguise
Saturn’s innermost moon Mimas may be hiding a vast subsurface ocean locked away beneath its icy surface, according to the results of a new study.
Mimas is but one of Saturn’s eclectic family of 63 confirmed moons, which come in a dizzying array of shapes and sizes, from the stress fractured form of Enceladus to the misshapen mass of Hyperion, which has a density significantly lower than water.
What makes Mimas unique — beyond the fact that it orbits closer to Saturn’s cloud surface than any other major moon — is the vast impact scar known as the Herschel Crater, which dominates its pockmarked features.
The cyclopean appearance granted by the 80 mile wide wound (130 km) has led many to nickname it Saturn’s Death Star moon, in reference to the iconic battlestation from Star Wars.
Now, a new study published in the journal Geophysical Research Letters has found evidence to suggest that Mimas is indeed no (normal) moon, but rather a stealthy ocean world in disguise.
Near the end of its almost 20-year mission, instruments aboard NASA’s Cassini spacecraft detected a subtle oscillation in the natural rotation of Mimas. This unexpected finding suggested either that Mimus’ played host to a strangely elongated rocky core, or, more likely, that its icy shell veiled a hidden subsurface ocean.
These theories prompted the authors of the new study to take a closer look at the violent impact that shaped Mimas’ Herschel Crater in order to see if they could reconcile that violent event with the presence of an interior ocean.
The team reconstructed its creation using advanced computer modelling software, and discovered that the presence of a subsurface ocean did indeed help explain both the shape and depth of the crater, along with the moon’s overall lack of surface fractures.
However, the models also showed that Mimas’ icy outer shell must have been at least 34 miles (55 km) thick in order 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.
Since the present day thickness of Mimas' icy outer shell is estimated to be at most 19 miles (30 km) deep, this finding suggests that the tiny moon has undergone significant warming since the impact, which has led to a decrease in the thickness of the ice.
The team also note that, whilst their findings support the possibility that an ocean could exist on Mimas, it is still possible that the moon is entirely frozen through both in the present day, and at the point of impact. In that scenario the strange characteristics of Mimas’ orbit would have to result from the shape of the moon’s core.
“Mimas seemed like an unlikely candidate, with its icy, heavily cratered surface marked by one giant impact crater that makes the small moon look much like the Death Star from Star Wars,” said Dr. Alyssa Rhoden of the 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 do not betray the ocean’s existence.”
The scientists note that future uncrewed missions to the Saturnian system would be valuable in revealing the secrets of Mimas’ evolution, and that the moon “may be the first example of a new pathway to forming potentially habitable ocean worlds”.
ign.com
