Galileo Views Io Eruption . ... Credit Copyright: The Galileo Project , JPL , NASA Explanation: Io's surface is active . Geyser-like eruptions from volcanoes on this Jovian moon were seen by both Voyager spacecraft in 1979 and were also spotted this year in late June by Galileo's camera from a distance of about 600,000 miles. The blue plume seen at the moon's edge (magnified in the inset) arises from Ra Patera , a large shield volcano, and extends about 60 miles above the surface. ...