didn't start out looking for an ocean on Callisto. According to Cochrane, the team was working on a different project, involving scanning Neptune's moon Triton to see if it has a subsurface ocean.

On Enceladus, saltwater is conveniently spewing out ... look at Mimas, and I said, “There’s no way that is an ocean moon.” Yet I realized I couldn’t refute the idea. I kept Mimas in my ...