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   January 2000 

Prometheus' fire

“Io makes Dante’s Inferno seem like another day in paradise,” said Dr. Alfred McEwen, a member of the Galileo imaging team, on Nov. 19, the day NASA released its latest images of Jupiter’s moon, Io—the most volcanically active body in our solar system. Galileo collected data for new, higher resolution images on Oct. 10, when the NASA craft dipped to a mere 611 kilometers above the surface of Io. The near-infared spectrometers used to collect imaging data were focused on Pele, Loki and Prometheus, the three most active volcanoes out of more than 100 on the moon. 

Prometheus, shown in the photo here, has been likened to Hawaii’s Kilauea volcano. Prometheus’ volcanic plume has migrated nearly 100 kilometers west of the location observed by Voyager in 1979 and has been erupting consistently for more than 20 years. New images reveal that what was previously thought to be a large lava flow is in part a lava-filled caldera 28 kilometers long and 14 kilometers wide. It is now believed that the lava is transported westward through lava tubes for approximately 100 kilometers before erupting onto the surface and creating a large plume. Kilauea’s lava-filled caldera is similar, but on a much smaller scale. Kilauea’s lava lake is about 100 meters across and lava is transported only 10 kilometers in lava tubes into the Pacific Ocean where steam plumes are formed.

Galileo flew even closer to Io at an altitude of 300 kilometers on Nov. 25.

—Laura Wright