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Moving Clouds

May 6, 2012

Changes in seasons bring changes in cloud cover — not just here on Earth, but on other worlds as well. On Saturn’s moon Titan, for example, a giant cloud system above the north pole vanished as winter gave way to spring.

The Cassini spacecraft discovered the cloud deck in late 2006 — near the middle of winter in Titan’s northern hemisphere. The clouds spanned about 1500 miles, so they looked like a beanie cap atop the big, cold moon.

Titan is so cold that the clouds were made not of water, but of ethane and methane — organic compounds that are gases in the warmer climate of Earth. It’s likely that some of these compounds were falling from the clouds as rain, filling cold lakes near the north pole.

The clouds remained in place throughout the rest of the northern winter — which, like all seasons on Titan, lasts about seven Earth years. But in 2009, as winter ended, the clouds began to vanish. By early spring they were gone, leaving the north pole with clear skies. But more clouds were popping up in the southern hemisphere, indicating that just as on Earth, the clouds on Titan change with the seasons.

On Titan, though, the seasonal differences may be more extreme. During summer, Titan’s lakes may evaporate, with the ethane and methane moving to the opposite hemisphere. There, they form fresh clouds that dump heavy rains on the surface, filling the lakes there — part of a constant back-and-forth cycle on this cold, intriguing moon.


Script by Damond Benningfield, Copyright 2012


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