Features

PASADENA — Twin volcanic plumes that rise 250 miles above the surface of Jupiter’s fiery moon Io appear in images taken by two NASA spacecraft and released Thursday. 

Scientists have known about one of the towering plumes for the past four years, as 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 in the act. 

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 just 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 in August when the spacecraft will pass just 224 miles above the area, going directly through the plume — if it’s still present. Unlike the risks that volcanic ash and debris pose to aircraft here on Earth, the plume is tenuous enough that it will not endanger Galileo. 

Io is the most volcanically active body in the solar system. Because Io orbits so close – 260,000 miles – to giant Jupiter, the planet’s gravitational tug constantly flexes the moon like a metal bar bent back and forth. That constant flexing 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.