Scientists: Jupiter's Moon Io A Volcanic And Electric Dynamo

MADISON, Wis. - More than 30 volcanoes spew lava, an eerie blue light erupts from torrid fountains, and a natural dynamo generates more electricity than every power plant in America combined. That's Io, a moon of Jupiter that is sort of an energy hell.

New photos from the Galileo satellite show lava glowing in red pools, scattered like an angry rash across the face of Io. Some eruptions give off a bluish light and, in black space just above, an arc of light is generated by power surges estimated at more than 400,000 volts.

It all comes from a combination of volcanic activity, magnetic-field generation of power and the enormous gravitational forces of Jupiter, said Paul Geissler of the Jet Propulsion Laboratory.

Tidal forces from Jupiter twist and contort little Io, creating frictional heat that erupts in at least 32 volcanoes, he said.

"Io is the most volcanically active body in the solar system," Geissler said yesterday at a meeting of the planetary division of the American Astronomical Society.

Enough lava flows every year on Io to cover the entire surface almost a half-inch deep, Geissler said. For this reason, the moon is the only major body in the solar system known to have no evidence of asteroid craters. The lava erases the impact marks, he said.

Pillon, a major volcano on Io, spews lava that is about 2,600 degrees Fahrenheit, hundreds of degrees hotter than volcanoes now active on Earth, Geissler said.

As it orbits Jupiter, Io intersects with powerful magnetic-field lines from the giant planet and acts like an enormous electrical generator. This natural dynamo creates more than a trillion watts of power - greater than the total output of all U.S. power stations, he said.

The power causes Io to glow when it is in Jupiter's shadow. Pictures from Galileo show the moon with a glimmering halo.

Near the surface, the combination of electricity and gases from the volcanoes creates an even more unusual sight, Geissler said. Sulfur dioxide venting from the volcanoes is energized by the charged particles from the electrical fields. The gas then glows a brilliant blue.

Io also has fields of red and green, generated when charged particles energize molecules of oxygen, hydrogen and other gases.

"This light show has been going on for a billion years," Geissler said, "and this is the first time it has ever been seen."

Io is 2,236 miles in diameter, slightly larger than the Earth's moon. It is one of four Jupiter satellites or moons discovered by Italian astronomer Galileo Galilei. Jupiter has at least a dozen smaller moons.