By finding the likely solution to one puzzle about Saturn's largest moon, Titan, astronomers think they have come upon an explanation for another: How Titan sustains an atmosphere rich in methane. New observations by the Cassini spacecraft and ground-based telescopes have focused on trying to understand the peculiar patterns of clouds on Titan. Clouds are rare there, except over the South Pole and in the mid-latitudes of the southern hemisphere. The polar clouds are stormy and persistent, with lifetimes of weeks. The other clouds, at a latitude the equivalent of the one that crosses New Zealand and Argentina, appear and rain out methane in a matter of hours or a few days as they stretch out downwind.