Callisto's watery secret
One of Jupiter's moons may hold an underground ocean.
One of Jupiter's largest moons, Callisto, may hold watery secrets beneath its surface, suggests a new analysis. The satellite's icy crust may be the planetary equivalent of a blanket, insulating an underground ocean.
Radioactivity at Callisto's core provides ample heat to keep water from freezing. But scientists believed that the heat would escape through the satellite's crust of ice and rock.
The first hints of Callisto's watery secret emerged in 1998. Data collected by sensors on the spacecraft Galileo revealed that the moon's magnetic field fluctuates as Jupiter turns. An underground ocean of salt water seemed the most plausible explanation, as salt water conducts electrical current, which could interact with Jupiter's magnetic field to produce the fluctuations.
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