moons
Image: NASAM

The aging spacecraft Galileo continues to send home informative snapshots of Jupiter's moons. Its latest series of images offer the closest view yet of Io, known for its ever-erupting volcanoes, oozing lava flows and jagged mountain ranges. The new pictures reveal another characteristic feature of this hostile world: sulfur-rich particles or crystals that blanket much of the satellite like snow. "We see this volatile material everywhere on Io where we've had a close-up look," said Alfred McEwen of the University of Arizona. "It looks like this volatile material is sublimating or eroding away by some means, yet it's still there. We'd like to know where it is coming from, how the surface layer is being supplied."

The scientists believe that heat from Io's active volcanoes helps redistribute the white pseudo-snow. Images reveal a bluish haze around the lava spreading from Io's Prometheus volcano (above). Arizona graduate student Moses Milazzo explains that the lava's heat turns the volatile solids into gas--and the haze is most likely representative of that gas crystallizing back into solid flakes of a sort. "We see the bright volatiles being redeposited up to about a kilometer away," he adds. One looming question is why this volatile material has not been lost into space over the years or has not become concentrated around Io's colder poles.