The Cassini spacecraft detected what appear to be lakes and ponds near Titan's equator. If so, one lake is almost forty miles long, 25 miles wide, and at least three feet deep. Natural processes on the moon's surface rain down methane mixed with hydrocarbons, but only near the poles. Near the moon's equator, natural processes evaporate the methane. So, after many millennia, any ancient equatorial methane lakes on Titan should have completely dried. The methane lakes' continued presence baffles astronomers, leaving them to face the difficult task of explaining it.
Caitlin Griffith, planetary scientist at the University of Arizona in Tucson, is lead author of the study results published in Nature. She told Nature News, "Lakes at the poles are easy to explain, but lakes in the tropics are not."