This image, taken by NASA's Galileo spacecraft,
     shows a new blue-colored volcanic plume extending
     about 100 kilometers (about 60 miles) into space
     from Jupiter's moon Io (see inset at lower left). The
     blue color of the plume is consistent with the
     presence of sulfur dioxide gas and 'snow' condensing
     from the gas as the plume expands and cools. Galileo
     images have also shown that the Ra Patera plume
     glows in the dark, perhaps due to the fluorescence of
     sulfur and oxygen ions created by the breaking apart
     of sulfur dioxide molecules by energetic particles in
     the Jovian magnetosphere. The images at right show
     a comparison of changes seen near the volcano Ra
     Patera since the Voyager spacecraft flybys of 1979
     (windows at right show Voyager image at top and
     Galileo image at bottom). This eruptive plume is an
     example of a new type of volcanic activity
     discovered during Voyager's flyby in 1979, believed
     to be geyser- like eruptions driven by sulfur dioxide
     or sulfur gas erupting and freezing in Io's extremely
     tenuous atmosphere. Volcanic eruptions on Earth
     cannot throw materials to such high altitudes. Ra
     Patera is the site of dramatic surface changes. An
     area around the volcano of about 40,000 square
     kilometers, area about the size of New Jersey, has
     been covered by new volcanic deposits. The image
     was taken in late June 28, 1996 from a distance of
     972,000 kilometers (604,000 miles). The Galileo
     mission is managed by NASA's Jet Propulsion
     Laboratory.