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Io's full disk
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High-altitude ionosphere found at Io by Galileo
News story originally written on October 23, 1996

Scientists participating in NASA's Galileo mission have discovered that the during its Io fly-by, Galileo spacecraft may have flown through an ionized region, or the ionosphere. This discovery suggests that Io's atmosphere is time variable and is made of volcanic gas raised to very high altitudes.

"Sensors on the spacecraft found a very dense region of ionized oxygen, sulfur and sulfur dioxide at 555 miles on Io that must be pumped into that region by Io's relentless volcanic activity," said Dr. Louis A. Frank of the University of Iowa, principal investigator on Galileo's plasma science experiment. "Instead of being swept away by Jupiter's rotating magnetosphere as anticipated, the ionized gases surprisingly remain with Io," he said.


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