Volcanic Plumes Seen on Jupiter Moon

PASADENA, Calif. (AP) - Scientists have known about one of the towering plumes for the past four years. It has continued to spew gas and dust from a volcano called Pele each time the Galileo probe has flown past Io.

But when Galileo was joined at Jupiter this winter by the spacecraft Cassini, the two probes caught a second plume.

Peering at Io in ultraviolet wavelengths on Jan. 1 and 2, Cassini spied the new plume near the moon's north pole. The discovery was the first of an active plume in that region and the first to rival Pele's plume in size.

Images taken days earlier by Galileo but transmitted to Earth earlier this month show a red ring circling a volcanic area called Tvashtar Catena. Scientists said the new ring of deposits makes Tvashtar the likely source of the new plume.

Scientists working on the National Aeronautics and Space Administration mission hope Galileo will give them a closer look at Tvashtar when the spacecraft passes just 224 miles above the area in August. The craft will fly directly through the plume - if it's still present.

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. That dynamic causes the moon's extreme volcanism.

Galileo has orbited Jupiter since 1995 and will continue to do so until NASA sends it plunging into the planet's atmosphere in 2003. Cassini swung past Jupiter this winter to gain a boost on its way to a 2005 arrival at Saturn.

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