February 2, 2007—Saturn's largest moon Titan is really living up to its name.

An image released today shows a huge swirling cloud roughly half the size of the United States over the moon's north pole. The formation—which is made up of ethane, methane, and other organic material—could be the source of methane lakes spotted near the pole last summer.

NASA's Cassini spacecraft captured the image of the 1,490-mile-diameter (2,400-kilometer-diameter) cloud on December 29, 2006. The cloud's presence fits predictions that Titan has a "methane cycle" similar to Earth's water cycle, with bodies of liquid methane evaporating and forming clouds that rain material back down on the surface.

"We knew this cloud had to be there but were amazed at its size and structure," Christophe Sotin of the University of Nantes in France and a member of the Cassini imaging team, said in a NASA release.

The cloud system will shift position with the moon's seasons, experts predict, and it will eventually migrate from the north pole to the south pole.

Ground-based observations suggest that total cloud activity on Titan lasts for about 25 years, then vanishes for a 4- to 5-year period. The massive cloud over the pole should be around for several more years before it disintegrates.

—Victoria Gilman

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