* Astronomy

NASA scientists are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre "runaway" process that is transporting vaporised water ice from the dark areas to the white areas of the Saturnian moon.
This "thermal segregation" model may explain many details of the moon's strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA's Cassini spacecraft.
Infrared observations from the flyby confirm that the dark material is warm enough (approximately minus 230 degrees Fahrenheit or 127 Kelvin) for very slow release of water vapour from water ice, and this process is probably a major factor in determining the distinct brightness boundaries.

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This image of Iapetus was taken by the Cassini space probe on September 11, 2007, when it was approximately 81,835 kilometres.


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Credit NASA

The image was taken using the UV2 and UV3 filters.

This is a 15-frame mosaic of most of Iapetus' trailing hemisphere, which was composed by Gordan Ugarkovic.



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Credit: NASA/JPL/Space Science Institute

This image was taken on Sept. 10, 2007, with the Cassini spacecraft narrow-angle camera at a distance of approximately 9,240 kilometres from Iapetus. Image scale is 55 meters per pixel.
The terrain seen here is located on the equator of Iapetus at approximately 199 degrees west longitude, in the transition region between the moon's bright and dark hemispheres. North is up.