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.