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Tuesday, August 31, 1999 Published at 16:23 GMT 17:23 UK


The changing face of Jupiter's moon

Io - tugged and pulled by gravity

Nasa has revealed the most detailed ever picture of Jupiter's closest large moon, Io.

The image shows how its surface is constantly remoulded by volcanic activity.

On July 3 Galileo flew nearer to Io than it has since entering orbit around Jupiter in 1995. During the encounter the spacecraft captured high-resolution images - 1.3 km per picture element - giving scientists a detailed view of Io's surface.

The colour image was created by combining data from near-infrared, green and violet filters in the spacecraft's camera to approximate what the human eye would see.

[ image: Small volcanoes not seen before]
Small volcanoes not seen before
It shows small-scale volcanic features which have not been previously seen.

Comparison of these images to previous ones reveals many changes due to volcanic activity.

The appearance of Io's surface is constantly altering as it is formed and reformed by lava flows of molten silicate rock caused by the gravitational tug of Jupiter's tides.

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