To help answer this, scientists instructed the robot spacecraft Galileo to take hourly pictures of this moon of Jupiter prior to its most recent encounter. The most obvious changes in Io are due to the changing amount of sunlight reflected from the moon to the spacecraft. More careful inspection does verify continuous volcanic plumes . The most prominent plume visible is from Prometheus, visible just below Io 's equator. On most browsers, the above picture will appear animated.
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