By the light of the fiery moon

larger   Culann Patera, one of the most colorful volcanic centers on Io, is the centerpiece of this mosaic of the best high-resolution, color view of the Jupiter moon yet returned by NASA's Galileo

Photos of Jupiter's Io reveal
land of sizzling lava lakes

In this story:

Sulfur plumes offer colorful show
Powerful tide lifts rocky surface
'Mountains up to 10 miles high'
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From staff and wire reports

WASHINGTON -- Unstable doesn't begin to describe Io, Jupiter's most volatile moon.

Within 42 hours, that moon's surface rises and falls by up to 300 feet. Poisonous gas shoots in the air to twice the height of Mount Everest.

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And don't mention temperatures. Io (pronounced EYE-o) is going through some type of climatic schizophrenia. On Io, lava lakes sizzle as hot as 3,000 degrees Fahrenheit (1,650 Celsius), while away from the volcanic pools, temperatures plummet to way below zero.

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The new information about this convulsing, shrinking, sizzling moon comes from recent close-up images taken by Galileo, one of NASA's spacecraft, during three recent flybys.

Io has "the greatest temperature range of anything in the solar system," said Alfred S. McEwen, a planetary geologist at the University of Arizona in Tucson and first author of a report that appeared in the journal Science.

But the temperatures are just the beginning of the horrendous conditions on Io.

Sulfuric smoke from volcanoes spews dozens of miles into the air. That gaseous type of sulfur probably recombines into larger molecules with a reddish appearance when they fall on Io's surface. Eventually the molecules rearrange themselves into a more stable configuration, which form ordinary pale yellow sulfur.

Unusual chemical reactions help produce the colorful display, according to scientists at NASA's Jet Propulsion Laboratory, which manages Galileo.

Io's diameter also keeps it in a state of flux. Io is 2,000 miles (3,220 kilometers) in diameter, about the size of the Earth's moon. It orbits about 260,000 miles (418,500 kilometers) 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.

In a 42-hour span, every point on Io goes from high tide to low tide, with its rocky surface rising and falling by up to 300 feet (90 meters) or more, said McEwen. This constant tidal motion is what triggers the endless volcanoes, he said.

"The dimensions of Io are constantly being squeezed and expanded," he said. "That's like bending a piece of metal back and forth -- it heats up."

"There are an awfully lot of quakes going on," said John R. Spencer of the Lowell Observatory in Flagstaff, Arizona, a co-author of the study. "If you were on Io, everything around you would be rising up and down. It would be like being on a boat out in the ocean."

Away from lava pools, temperatures on Io plummet to minus 250 degrees Fahrenheit. BRRRRR!!!!

Io hardly has any atmosphere, and what atmosphere it does have is virtually all poisonous.

Spencer said Io spews out so much sulfur gas that the entire complex of moons and natural satellites around Jupiter is affected.

"There is a huge cloud of glowing gas that has escaped from Io and is just hanging around in Jupiter's magnetosphere now," Spencer said. Studies suggest that sulfuric acid deposits, possibly from Io, cover large areas of Europa, one of Io's sister moons.

Spencer said that, by some estimates, Io is slowly shrinking, at the rate of about 1 ton every second, from the loss of rock vaporized into space by the volcanic heat.

During the last 4.5 billion years -- the age of the solar system -- volcanism has caused Io to shrink by about two miles (3.2 kilometers), Spencer said. Given the moon's size, however, he said it is unlikely that Io "is ever going to just boil away to nothing."

But McEwen said it is clear that Io is melting and re-melting itself, time after time after time.

"We estimate that Io has been completely melted at least 400 times -- and perhaps as many as 4,000 times -- over the age of the solar system," McEwen said.

It is unknown how thick Io's crust is or how far below is the layer of molten rock that spews to the surface as lava. But McEwen said the moon has to have a crustal layer of about 18 miles (29 kilometers) thick to support its impressive range of mountains.

"It has mountains up to 10 miles [16 kilometers] high," McEwen said. "That takes considerable strength [in the crust]."

The Associated Press contributed to this report.