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.

November 29, 1996
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Io: The Fissure King?
Voyager Project, Galileo Project, JPL, NASA

Explanation: Is Io the solar system's Fissure King? Well, probably not ... but it is the most active volcanic moon. Active volcanoes on Jupiter's moon Io were a surprise discovery of the Voyager missions of the late 1970s. The extent of Io's volcanic activity today is being investigated close-up by the Galileo spacecraft currently exploring the Jovian system. The two frames above show a roughly 300 mile square area around the Io volcano called Marduk. The left-hand view of Marduk was made by Voyager in 1979, the right-hand view by Galileo earlier this year. A comparison reveals that dramatic changes have occured, including the creation of a dark, linear feature running diagonally through the Galileo image that is probably a huge volcanic fissure.

Tomorrow's picture: Aurora Astern

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
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