By Greg Clark
Arizona Daily Wildcat
November 6, 1997

Arizona-sized volcano erupts on Jupiter moon

Arizona Daily Wildcat Photo courtesy of Alfred McEwen/Galileo Imaging Team The photo on the left shows the surface of Jupiter's moon Io as seen by the Galileo spacecraft in April. The photo on the right, taken by Galileo in September, shows a newly-formed volcano, almost as big as Arizona, in the upper right. The ringed dark spo t near the center is the active volcano Pele, which has existed at least since the Voyager spacecraft passed Jupiter in 1979.

NASA released images yesterday of one of the solar system's largest known active volcanoes on Jupiter's moon Io - a fire-belching mountain the size of Arizona.

The images, taken in September by the Galileo spacecraft orbiting Jupiter, show a giant gray spot about 249 miles in diameter with lava flows in the center nearly 43 miles long, said Alfred McEwen, University of Arizona planetary scientist. The volcano is in its infancy; it did not exist last April.

"This is the largest surface change on Io observed by Galileo during its entire two-year tour of the Jovian system," McEwen said.

McEwen is a member of the Galileo imaging team and leader of the team observations for Io. Galileo passed Io last April and sent back images of a surface bearing no trace of the upstart volcano. But in June, scientists noticed a major new eruption on the moon.

They received images from Galileo revealing a new heat source and a volcanic plume reaching about 75 miles above the moon's surface, but the spacecraft was too far away to provide details of the event.

McEwen said the ring of debris ejected from the volcano may allow scientists to measure the composition of Io's interior.

"Io is an experiment in planetary physics and how planets react when extensively heated," he said.

He explained that Io may provide a demonstration of how some of the massive volcanic events on Earth occurred.

"But mostly, it's just way cool," he said.

Galileo was launched in 1989 and reached its orbit around Jupiter in December 1995.

It will complete the first two-year stage of its mission today when it sweeps just 1,269 miles from Europa, a Jovian moon whose frozen surface may cover vast oceans of liquid water.