One of the lesser moons of Saturn, Mimas, has been largely viewed as a boring lump of ice. But a new discovery has suddenly turned this moon into hot property: its rotational wobble turns out to be far stronger than expected. Mimas is almost perfectly spherical, so a robust wobble implies that something intriguing is going on below its surface… and that something is very likely to be sloshing. The most likely explanation for the wobble would be an internal ocean starting between 24 and 31 kilometers below the moon’s surface.
This would be something of a puzzle in a moon as small as Mimas — how could a liquid ocean remain warm enough for billions of years? One possibility is that the elliptical orbit of Mimas creates tidal friction strong enough to maintain a warm core. More →