Imagine a frigid world where complex hydrocarbon particles clump together in the thick smog-like atmosphere and fall like black snow onto a light water ice surface. Occasional methane rains and methane springs that emerge from the side of hills wash some of the particles off higher ground and concentrate them in river channels. These rivers flow through the hills to lower-lying areas. Some of the liquid methane with its hydrocarbon particle load collects into pools and lakes. Eventually, the liquid evaporates or soaks into the ground, until the pools are dry, waiting for the next rainfall.

Titan is that world, revealed this morning by scientists involved with the Huygens space probe mission. After last week’s successful landing on the exotic Saturnian moon, data from the probe’s mass spectrometer, imaging system and other sensors confirmed the presence of liquid methane on or near the surface of Titan. Because Huygens detected methane just a few centimeters below the surface, scientists believe that it may have rained recently in the area, perhaps in the few days or weeks before the landing.

Marty Tomasko, Principle Investigator for the Descent Imager-Spectral Radiometer (DISR) on board Huygens, stated that Titan was a world of “earth-like processes” using “exotic materials.” Instead of water, methane is the primary liquid at work on the surface of the moon, and rather than silicate rocks, the rocks of Titan are made of water ice. They interact to create breathtaking vistas such as those near the Huygens landing site: river channels flowing down ridges to temporary lowland lakes with distinct shorelines.

Because no current pools of liquid were detected on the surface, the region photographed by Huygens may be a relatively more arid region of Titan, though little is known about the rest of the moon to substantiate this theory. The region may resemble the deserts of Arizona, where liquid water plays an important role in shaping the landscape despite the aridness, resulting in dry river beds between episodes of seasonal flooding.