Voyage to Saturn

The rain comes just once every thousand years, in torrents of liquid methane. The noxious air dims sunshine to an eternal orange twilight. The cold—290 degrees below zero Fahrenheit—is a lethal assault. And beyond the hazy sky looms the ringed planet Saturn.

Yet here on Saturn's outsize moon Titan is a world eerily like our own."Titan is a Peter Pan world," says Tobias Owen of the University of Hawaii's Institute for Astronomy. "It's got all the materials and elements to develop into a planet like Earth," he says, "but it never had the chance to grow up." The dense atmosphere is filled with hydrocarbon smog, "like L.A. on a bad day," Owen says. The rare methane monsoons create sudden rivers that cut deep channels in Titan's low hills and run down to a great sandy plain. Like Earth, Titan may have geologic activity and volcanism—a slow, chilly version that erupts a lavalike mix of half-melted water and ammonia. Most tantalizing of all, Titan's gentle winds carry a rich brew of organic molecules, some reminiscent of compounds that provided the raw material for life on Earth.