Io is one of Jupiter's moons. There are more than 50 moons orbiting Jupiter. Io is a little larger than Earth's moon. The blue area rising from Io's surface comes from the plume of an active volcano. The volcanoes on Io erupt more powerfully than volcanoes anywhere else in the solar system. Volcano plumes on Io rise almost 200 miles above the surface.
NASA's Voyager 1 spacecraft took this image when it flew past Jupiter and its moons in 1979.
To learn more about Io, go to http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Io