Scientists had known about one plume for four years because it has spewed gas and dust from a volcano called Pele each time the Galileo probe has flown past Io. But when Cassini probe joined Galileo this winter the two probes discovered a second plume and a bright red ring of fresh surface deposits surrounding its source. The new plume is near the moon's north pole, the first time an active plume has been found in that region. Scientists were surprised to find one there because all previous active plumes on Io were in equatorial regions. Images taken by Galileo but transmitted to Earth earlier this month show a red ring circling a volcanic feature called Tvashtar Catena.
Scientists say the new ring of deposits makes that area the likely source of the new plume.
National Aeronautics and Space Administration scientists hope Galileo will provide them with a closer look at Tvashtar when the spacecraft passes just 224 miles above the area in August. It will fly directly through the plume - if it's still present. Passing through the plume could give scientists an opportunity to analyze the makeup of the plume. Io is the most volcanically active body in the solar system. Because it orbits so close to giant Jupiter, the planet's gravitational tug constantly flexes the moon like a metal bar bent back and forth causing moon's extreme volcanism.