by Brian Thomas, M.S. 

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.1 She told Nature News, “Lakes at the poles are easy to explain, but lakes in the tropics are not.”2

These observations are easy to explain if evaporation has only been occurring for thousands, not billions of years. How could methane lakes still exist on Titan’s equator after billions of years of evaporation?

“Because tropical lakes on Titan should evaporate over a period of just a few thousand years, the researchers argue that these ponds and lakes are being replenished by subsurface oases of liquid methane,” according to Nature News.2 That kind of argument is very familiar.

For example, in 2008 Cassini discovered frozen carbon dioxide on Iapetus, another of Saturn’s moons, even though sixty-trillion tons of the carbon dioxide are lost to space during each orbit. To explain this, researchers proposed that it is replenished from below the surface or from impacts, but neither explanation has supporting evidence.3

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