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FOR IMMEDIATE RELEASE: January 2000

Lowell Observatory Astronomer Spots Eruption on Io while Galileo Captures it in Space

On November 25, 1999, Jupiter expert Dr. John Spencer of Lowell Observatory, working with astronomer Glenn Orton of the Jet Propulsion Laboratory at NASA's Infrared Telescope Facility at Mauna Kea, Hawaii, discovered a large volcanic eruption on Io, one of Jupiter's satellites.  Their infrared photo of the eruption was taken just hours after a close Io flyby by NASA's Galileo spacecraft. Spencer's Earth-based observations over many years show that this type of eruption occurs only about 20% of the time anywhere on Io, but by amazing good luck, Galileo caught a close-up view of the eruption in its narrow field of view as it flew past.

The Galileo spacecraft observed the fiery lava fountain shooting more than a mile above the moon's surface. The images show a curtain of lava erupting within a giant volcanic crater. "Catching these fountains was a one-in-500-chance observation," said Galileo scientist Dr. Alfred McEwen from the University of Arizona in Tucson.

Spencer was delighted but not entirely surprised by what Galileo saw. He and former Lowell Observatory astronomer John Stansberry had inferred the existence of lava fountains on Io from their earlier Earth-based observations, but, he said, "it's incredible to see that idea confirmed so spectacularly by Galileo." The fact that the same eruption was recorded by spacecraft as well as by earth-based observing is a boon to the
research being done on Io. By combining the data, scientists have their best chance ever to pin down temperatures of the extremely hot lava on Io.

The following is a false-color infrared image of the sunlit disk of Jupiter's moon Io
[ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02522 ].  The bright spot at the 1 o'clock position is the same lava fountain seen close-up by Galileo's camera, but in this case it is seen from Earth at a distance of 630 million kilometers (390 million miles).