Io's Sodium Cloud . ... Credit Copyright: Galileo Project , JPL , NASA Explanation: Io has its own cloud. Jupiter 's most active moon is visible on the left of the above false-color photograph , with its left side illuminated by sunlight. ... Here a plume of gas from the active volcano Prometheus also reflects sunlight. ... Surrounding the moon is a yellow haze originating from gas ejected by Io's volcanos . Sodium atoms in the gas cloud are particulary efficient at reflecting yellow light . ...