|Photo by University of Arizona/NASA/JPL|
A typical day on Jupiter's moon Io is a sojourn into Dante's Inferno,
complete with flowing lava and blasts of hot ash. Now it appears that equally nasty ice dwells amid the fire, says planetary scientist Alfred McEwen of the University of Arizona. Studying recent images from the Galileo
spacecraft (right), McEwen found that much of Io's surface is covered with a fluffy blanket of snow, up to half a mile thick in some areas. But unlike the stuff that piles up in your driveway, Io's blizzards are composed of sulfur dioxide and other noxious, sulfur-rich molecules.
The downfall originates in the gas plumes that spew from hundreds of erupting volcanoes. Although Io is the most volcanically active body in the solar system, temperatures plummet to about -280 degrees Fahrenheit a short distance from the hot spots. Sulfur dioxide, which freezes at about -225 degrees, quickly turns to ice, bringing together the worst of both worlds. "The lava flows can come within meters of the snow before vaporizing it," says McEwen.