On Saturn’s Moon Titan, It’s Raining Methane

Imagine a world where the average daytime temperature is -179°C, and torrential rains of liquid methane fall from the skies, forming vast but shallow pools that cover an area larger than the Great Lakes [ScienceNOW Daily News].

That’s the vision of the Saturnian moon Titan provided by the NASA spacecraft Cassini, which has been exploring Saturn and its satellites since 2004. In the latest findings, Cassini scientists have determined that Titan has seasonal weather patterns in which fierce storms fill up the methane lakes. “We see clouds that behave very much as clouds on Earth, and we see evidence of flooding on the surface, just as a lot of people in the [U.S.] Midwest saw last year” [National Geographic News], researcher Elizabeth Turtle said.

The researchers compared images taken in July 2004 and June 2005, and spotted both low-lying clouds and newly formed dark areas representing lakes of hydrocarbons. But the source of the methane that rains down through Titan’s thick atmosphere is still something of a mystery, as the methane should be quickly broken down by UV radiation. According to the researchers, the source most likely lies beneath the surface of the moon. There may be volcanoes releasing plumes of methane, instead of lava, from the interior. That methane, a leftover from the primordial gas cloud that formed Titan, could be plentiful enough to sustain the rainy weather [ScienceNOW Daily News].

The transitory lakes, described in Geophysical Research Letters [subscription required], formed in the south during summer in Titan’s southern hemisphere. But the seasons are slowly shifting, and researchers hope to keep watching the moon to see how rainfall and lake formation are affected. Says researcher Tony DelGenio: “The longer we stay, the more we get to see the seasons progress…. A few years down the line, in 2015, 2016, and 2017—if we last that long—we may be able to see the northern summer” [National Geographic News]. Cassini completed its originally scheduled four-year mission last year, but is now engaged in an extended mission through 2010. Since the craft is still in good working order and since it continues to send back fascinating observations of the Saturnian system, researchers hope NASA will continue to fund it past the 2010 cut-off date.

Image: Space Science Institute/NASA/JPL