During the long, dark winter nights at high Earth latitudes, the Aurora Borealis puts on a dazzling, magnetically-induced light show above the Arctic Circle. The aurora's best effort though, is but a dim flicker compared to the brilliant, flashing firestorm of atmospheric lights that an observer on Jupiter's innermost moon Io would see.

Last fall, a team of American and Taiwanese scientists working with data from the Galileo spacecraft turned their attention to Galileo's observations of Io as the satellite passed through a solar eclipse. As the moon was shaded by Jupiter's shadow, the researchers noticed three distinct patterns of red, blue and green aurora-like lights glowing in Io's atmosphere.

Now the group is announcing that the light effects are the result of an energetic interaction between Io's atmosphere and Jupiter's powerful magnetic field. The results of a detailed study of the Galileo data are being published in this week's issue of the journal Science.

Paul Geissler, a planetary scientist at the University of Arizona's Lunar and Planetary Laboratory in Tucson, Ariz., is the lead author on the article. He said the eclipse was an outstanding opportunity to view Io's light show. Without interference from bright, reflected sunlight, the colorful displays were clearly visible, he said.

"These are gasses that are excited by the impact of charged particles, and we see this at visible wavelengths," Geissler said in an interview Wednesday.

The brightest of the glimmering spots are two blue glows that extend above volcanic plumes on opposite sides of Io. These are umbrella-shaped structures that extend as much as 500 miles (800 kilometers) above Io's surface, said Alfred McEwen a co-author who is also at Arizona's Lunar and Planetary Lab.

These blue glows almost certainly emit from sulfur dioxide that rises above volcanoes, Geissler said. They are bright enough that they could be seen with the naked eye anywhere in the Jovian system. "If you were hanging on to Gallileo and looking over its shoulder, the blue glows in particular would knock your socks off," he said.

The red light appears as a ring that circles the moon, but it is brightest at one or another of the poles. The bright pole fluctuates over a 13-hour period. First the north pole is brightest, then the south pole.

Geissler and his colleagues believe this red is emitted by oxygen in Io's atmosphere, and that the fluctuation in brightness is a reaction to a periodic wobble in Jupiter's magnetic field.

In the background, over Io's entire globe, the atmosphere glows green, a glint that dims noticeably about 30 minutes after the moon enters eclipse. Most likely, this is due to a contracting of Io's atmosphere as it cools, Geissler said. Io's atmosphere is probably primarily composed of sulfur dioxide, scientists believe. It expands when warmed by sunlight, and changes phase from surface ice to gas during the day. As the gas cools during an eclipse or during the Io night, it contracts with some condensing back to frost.

Daytime highs on Io are about minus 225 degrees Fahrenheit while the chill at night approaches minus 300 degrees.

As the atmosphere shrinks, and as it cools, there is less gas to react with Jupiter's magnetic radiation, and thus, the glow dims, Geissler and his colleagues speculate.

Scientists will discover more about Io during further Galileo orbits of Jupiter. The spacecraft will soon enter the Io phase of its mission, in which the probe descends in its Jupiter orbit falling closer and closer to Io.