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Closeup of an Io Volcano

In 1979, one of NASA's Voyager spacecraft made a spectacular
and unexpected discovery. Io, the innermost Galilean moon of Jupiter, was covered
with volcanoes and some of them were erupting! In all, Voyager 1 observed nine
volcanic eruptions during its encounter with the moon. When Voyager 2 flew past
four months later it was able to confirm that at least six of them were still erupting.
This Voyager image of Ra Patera, a large shield volcano, shows colorful flows up
to about 200 miles long emanating from the dark central volcanic vent.