On Wednesday, Nature released a paper providing evidence that Saturn's moon Mimas has a subsurface ocean beneath its heavily cratered crust. The evidence for this ocean comes in the form of orbital oddities that are seemingly impossible to explain by anything other than the presence of an ocean.
Because of its proximity to Saturn, the moon is tidally locked to the planet so that its rotation is synchronized with its orbit, and one face of the moon constantly faces the planet's surface. Data from the Cassini mission, however, indicated that the synchronization isn't exact. Slight wobbles in the rotation mean that after some orbits, the rotation is slightly faster; after others, it has slowed down.
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