Moon and Saturn
 Saturn's smog-encircled moon Titan hovers behind the planet's rings in this recent image from the Cassini spacecraft. The smaller moon Epimetheus is just above Titan. Using radar and other instruments, Cassini has peered through Titan's thick atmosphere and discovered that hundreds of lakes dot the regions around its north and south poles. The lakes probably are filled with liquid methane. [NASA/JPL/SSI]
Saturn has a bunch of moons of its own, including one of the largest and most intriguing in the solar system. Titan is about half again as big as our Moon. What makes it intriguing, though, is that it's like a supercold version of Earth.
Because it's so far from the Sun, Titan's surface temperature is hundreds of degrees below zero. Yet the big moon has an atmosphere that's thicker than Earth's. And its surface is altered by falling and flowing liquids -- not water, which is frozen as hard as rock, but liquid methane and ethane.
Using radar to peer through Titan's hazy atmosphere, the Cassini spacecraft has mapped hundreds of lakes and seas on Titan. Most of them are in the far north, although the craft is starting to look at the far south, too. The largest is bigger than Lake Superior.
The lakes and seas are filled by a rain of methane and ethane. These supercold liquids also carve rivers, just like the rains on Earth. These rivers sculpt Titan's terrain.
As the seasons on Titan change, the methane and ethane evaporate and form clouds, which then rain on other areas, filling other lakes and seas. It's a chilly cycle that just keeps repeating -- just like the cycle of water here on Earth.
Script by Damond Benningfield, Copyright 2007
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