This photograph of Jupiter's satellite Io shows what appears to be a volcanic caldera that is venting gasses (the bright blue patch at left center).  In the photo is a network of volcanic calderas with dark floors linked by bright red materials.  The northernmost caldera has a bright blue patch on the floor.  Scientists believe the bright blue patch may be clouds of gas issuing from volcanic vents.  The gas clouds may condense to form extremely fine particles that appear blue.  Since Voyager 1's infrared spectrometer has discovered sulfur dioxide on Io, it is possible that sulfur dioxide is the main component of the clouds.  Sulfur dioxide clouds would rapidly freeze and snow back to the surface.  It is also possible that dark areas in the floors of the calderas are pools of molten sulfur, a very dark form of sulfur.  The picture was taken March 5, 1979, as Voyager 1 approached Io.  Photo was taken from 80,500 miles (129,600 kilometers).  The Voyager project is managed and controlled for NASA's Office of Space Science by the Jet Propulsion Laboratory.