The outer solar system is awash with liquid water. A briny ocean is concealed beneath the icy crust of Jupiter’s fourth largest moon, Europa — with more water than all of Earth’s oceans combined. A subsurface sea on Saturn’s moon Enceladus spews plumes of water vapor into space. And there are tantalizing hints that oceans could exist on Ganymede, Callisto, Titan and other distant moons, too.
Now another moon appears to be secretly flooded. Saturn’s moon Mimas, known for its uncanny resemblance to the Star Wars Death Star, might harbor liquid water beneath its icy shell. If true, similar seas could be hiding in plain sight, and the outer solar system may be far more habitable than previously thought.
In 2014, scientists first published evidence that Mimas might be a watery world — submerging the community in a decade-long debate. Many, including Alyssa Rhoden, a planetary scientist now at the Southwest Research Institute in Boulder, Colorado, were highly skeptical of the possibility. Their reasoning was simple: Mimas’ heavily cratered surface showed no signs of an internal ocean. As with Enceladus, Saturn’s gravity should churn the ocean waters within Mimas, causing large cracks to appear in the surface ice. No such fractures have been seen.
The tides might now have turned. Two studies, one by Rhoden and colleagues and another by Valéry Lainey of the Paris Observatory and colleagues, make a stronger case for an ocean and even explain the conundrum at the surface. Together, the research suggests that Mimas may have a young and changing ocean. If so, it raises the prospect of an outer solar system rife with activity. That possibility is what most excites Rhoden, who spoke with Knowable Magazine about the potential ocean and why it could be such a boon for scientists.
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