The black areas on this view of Titan's equator are large methane lakes.… (JPL/NASA )
Infrared imaging by JPL's Cassini spacecraft has shown the existence of large methane lakes near the equator of Saturn's moon Titan. One of them is about the size of Utah's Great Salt Lake at its lowest recorded level and is at least three feet deep. The spacecraft also discovered smaller, shallower "ponds" nearby similar to marshes on Earth, with knee- to ankle-level depths.
Astronomers have previously observed large methane lakes near Titan's poles, but the discovery of the "tropical" lakes is a surprise because it was generally assumed that this region was too warm to allow such lakes to exist for any length of time. Titan's weather system is similar to Earth's in one respect, but with liquid methane instead of water. The methane near the equator evaporates and is transported by winds to the poles, where it condenses back into a liquid. On Earth, the water is carried back to the equator by ocean currents, but there is no comparable mechanism on Titan, so researchers have assumed there could be no large bodies of methane near the equator.
But a team headed by planetary scientist Caitlin Griffith of the University of Arizona at Tucson reported in the journal Nature that they observed a large black area, covering about 927 square miles, at the equator and near where Cassini's Huygens probe had landed on the surface. The black region is characteristic of liquid methane. Because the methane evaporates readily, Griffith and her colleagues concluded that there is an underground "aquifer" of methane that continually feeds the lakes, dampening the ground over large areas. In effect, she said, "Titan may have oases."
Like water vapor, which dissociates in the upper atmosphere to form ozone, methane is also dissociated by sunlight to produce reactive carbon atoms that can combine to form organic chemicals such as amino acids. Such compounds have been detected in Titan's atmosphere and are the basis of some researchers' speculation that Titan may harbor life forms of some sort.