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