The images, taken between July 1999 and February, provide an unprecedented look into the fiery volcanic outbursts of the moon Io. They reveal parallels to volcanism on Earth and provide clues to the planet s mineral composition. Another image shows the cracked icy surface of the moon Europa, which may help settle the longstanding question of whether a liquid, perhaps life-supporting ocean lies below. Galileo has been orbiting Jupiter and its moons since December 1995. The first image, above, depicts volcanic craters, lava flows and cliffs on Io's south pole.
Calderas are depressions that form during volcanic eruptions.
Two of these three calderas are surrounded by yellow material, which may have been thrown out of the calderas by explosive eruptions. The bright, white material is thought to be sulfur-rich frost. It may be formed when liquid sulfur dioxide seeps out at the base of mountain, vaporizes into a plume of gas, and then condenses again on the surface. The second image of Io reveals lava flows similar to those found in Hawaii. The similarity to Hawaii s lava flows suggests that the floor of the caldera has been covered by a combination of lava flows and lava lakes.