Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 28, 1997
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Io's Sodium Cloud
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. But what is happening on Io's right side? Here a plume of gas from the active volcano Prometheus also reflects sunlight. A second active volcano, Pele, is also visible: marked by the red spot just below Io's center. 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. Several points of light are background stars.

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Official: Phillip Newman. Specific rights apply.
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& Michigan Tech. U.

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