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Soggy Moon

May 18, 2011

When you visit the tropics, it's a good idea to take along an umbrella -- you're probably going to get wet. And right now, that applies not just to Earth, but to the largest moon of the planet Saturn.

Titan is the only moon in the solar system with a thick atmosphere -- a blanket of nitrogen mixed with smatterings of methane and other hydrocarbons. The atmosphere is denser than Earth's, and a lot colder -- close to minus-300 degrees Fahrenheit.

At those temperatures, the methane condenses to form clouds. And like the clouds here on Earth, they sometimes produce rain -- enough to carve rivers and fill big lakes.

Over the last few years, the Cassini spacecraft has watched the climate on Titan change. Early on, most of the clouds appeared at high latitudes. Recently, though, they've been concentrated more in the tropics -- around the moon's equator. They've dumped so much rain that they've darkened some of the giant dunes that girdle the equator.

The change is caused by a change in seasons -- it's now early spring in Titan's northern hemisphere -- the equivalent of about the middle of April here on Earth. As the season progresses, the weather patterns change -- bringing heavy rains to the tropics on this frigid moon.

Saturn is high in the southern sky at nightfall, and looks like a bright golden star. One of the stars of Virgo is just a whisker away. Titan is visible through a telescope, and looks like a tiny star quite close to the bright planet.


Script by Damond Benningfield, Copyright 2011


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