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Jovian moon in tumult, photos show

Jupiter's moon Io, the most volcanically active body in the solar system, is a world of multicolored lava erupting constantly in showers, fountains and clouds of poison gas, according to new close-up photos.

The Galileo spacecraft, in orbit of Jupiter, has made three close flybys of Io, snapping dramatic photos and taking instrument readings of the bizarre moon. It found oceans of soupy lava, molten rock spewing from superheated geysers and vast sulfur plains, like fields of yellow snow, punctuated with streaks of green and spots of vivid red.

It is a world where there is never, by Earth standards, a pleasant day, says Alfred S. McEwen, a planetary geologist at the University of Arizona, Tucson, and first author of a report appearing today in the journal Science.

Away from the volcanic vents, temperatures drop to minus 280 degrees, while in the midst of a lava lake the heat could reach almost 3,000 degrees Fahrenheit. This is far colder than the Earth's poles and far hotter than the most searing terrestrial lava.

"This is the greatest temperature range of anything in the solar system," McEwen said.

Io is 2,000 miles in diameter, about the size of the Earth's moon. It orbits about 260,000 miles above Jupiter, closer to the giant planet than the other three major moons, Europa, Ganymede and Callisto.

As a result, said McEwen, Io is constantly being churned and tortured by the gravitational, or tidal forces, of its mother planet and its sister moons.

Every 42 hours, every point on Io goes from high tide to low tide, with its rocky surface rising and falling by 300 feet or more, said McEwen. This constant tidal motion is what triggers the endless volcanoes, he said.

"There are an awfully lot of quakes going on," said John R. Spencer of the Lowell Observatory, Flagstaff, Ariz., a co-author of the study. "If you were on Io, everything around you would be rising up and down by at least 30 meters (about 90 feet) every day. It would be like being on a boat out in the ocean."

Shuttle to launch today

The shuttle Atlantis was scheduled to lift off at 6:12 a.m. today with new batteries and other replacement parts for the international space station, which also will get a boost in orbit from the shuttle.