… And Io Yields Still More Surprises

JUL 01, 1996

Almost four centuries after Galileo’s telescope revealed moons orbiting Jupiter, those same moons are revealing their secrets to the Galileo spacecraft‐starting with Io’s differentiated structure and magnetic properties.

DOI: 10.1063/1.2807681

Ray Ladbury

Researchers have come to expect spectacular surprises from Io, the innermost of Jupiter’s Galilean satellites. The Voyager missions revealed Io to be the most volcanically active object in the Solar System. Voyager also revealed the importance of Io’s interactions with Jupiter’s magneto‐sphere, which generate a potential of 400 kV across the moon’s diameter and currents of over a million amperes between Io and Jupiter’s ionosphere. As a result of this past performance, researchers eagerly waited for Galileo to pass within 900 km of Io, a factor of 20 closer than any of Voyager’s flyby’s. Initial analysis of the data indicates that, once again, Io has not disappointed.