A decade ago the Cassini orbiter spotted gas and ice spewing from the south polar region of Saturn’s moon Enceladus. Subsequent investigations revealed that the ice is salty, a result indicating that the ice originated from a liquid ocean between Enceladus’s frozen surface and its silicate core. Now Peter Thomas (Cornell University) and his colleagues have analyzed more than seven years of Cassini surface observations and shown that the ocean is not localized at the polar region of Enceladus; rather, it is global. The figure shows some of the several hundred surface features tracked by the researchers. To first approximation, Enceladus, like our Moon, presents one face to its planet. But because Enceladus is a bit out of round, Saturn torques the satellite and induces a so-called libration, a wobble in the Enceladean hemisphere visible from Saturn. For a localized ocean, the icy surface of Enceladus and its core would...

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