Mimas, Saturn’s enigmatic moon, is extremely deceiving. The small moon is dominated by an 80-mile-wide crater, which gives it the appearance of the ominous Star Wars Death Star – a space station with a planet-destroying weapon. Mimas, on the other hand, looks to be a frozen lump of ice.
Cracked surfaces or telltale plumes erupting from the ground on other moons, such as Saturn’s Enceladus and Jupiter’s Europa, provide persuasive evidence for sub-surface oceans. Mimas doesn’t give out any hints of being near the sea.
“There’s certainly an engine going on these moons when you look at Enceladus and Europa,” Alyssa Rhoden, a planetary scientist who studies ocean worlds, told Mashable. “When you look at Mimas, it can’t possible be an ocean world,” says the author.
So Rhoden reasoned. Appearances can be deceiving. Rhoden and her colleague describe how they discovered evidence for an ocean beneath Mimas’ icy crust in a recent paper published in the planetary science journal Icarus. After all, the moon isn’t a solid block of ice.
Mimas does have a feature that allows it to harbor an ocean. Its orbit around Saturn is highly eccentric, which means it is towed and stretched as it swings near to the planet’s enormous gravitational attraction before orbiting farther away. (It just takes 22 hours and 36 minutes for each orbit!) In ocean worlds like Europa, this process, known as “tidal heating,” generates enormous amounts of heat.
With this in mind, Rhoden, a principal scientist at the Southwest Research Institute, followed up on a previous detection of a small wobble in Mimas’ orbit around Saturn. This wobbling could be caused by an icy sea sloshing inside Mimas. Is it possible that tidal heating melted enough ice inside Mimas to form a sea? If that’s the case, neither too much nor too little heat (which would melt the freezing shell) could exist (then the ocean would freeze).
If there existed an ocean inside Mimas substantial enough to cause its wobble, the water would be trapped beneath an icy shell 14 to 20 miles thick, according to the experts. As a result, they did computer models to see how tidal heating would affect the ice on Mimas. Surprisingly, it revealed an ocean buried behind 14 to 20 miles of thick ice.
“We arrived at the exact right quantity,” Rhoden remarked. This isn’t conclusive proof, Rhoden emphasizes, that Mimas is home to an ocean. However, based on the facts available, there is now compelling evidence that an ocean may exist there.
Oceans, as we know them on Earth, are vastly different environments teeming with life. According to NASA, “water is at the top of the list of components that make life possible.” Tidal heating may eventually allow life to thrive on ocean worlds like Europa, despite the fact that there is no evidence of life outside of Earth. “Tidal heating could be driving a mechanism that circulates water and nutrients between the moon’s rocky interior, ice shell, and ocean, resulting in a watery environment rich in chemistry suitable to life,” NASA stated.
The hunt for life in solar systems is sometimes limited down to “habitable zones,” which are relatively small places where liquid water could exist on a planet’s surface. The habitable zone of our solar system, for example, includes Earth.
Europa and Enceladus, which are located in the icy regions of our solar system, are far from being livable. However, these worlds have oceans. And it’s possible that life has sprung up there.
“Habitability isn’t a single swath of the solar system,” Rhoden explained. “There are a number of various ways life could emerge.”