Saturn’s Moon Titan is Wetter Than We Thought

Saturn's third-largest moon, Dione, is visible through the haze of its largest moon, Titan, with Saturn and its rings in the background. New data suggests Titan has lakes in its tropical regions. Photo Credit: NASA/JPL-Caltech/Space Science Institute

Saturn’s moon Titan is slowly giving up its secrets. Last week, scientists found evidence for tropical lakes; not the temperate vacation spots we enjoy on Earth but liquid methane deposits at latitudes equivalent to our Tropic of Cancer and Tropic of Capricorn, which are far from balmy at about -300F.  Found in the region known as Shangri-La, the discovery surprised scientists and is changing our understanding of the small moon. 

Until now, scientists thought Titan had methane lakes at its poles and vast sand dunes around the tropics. Previous models of methane’s cycle suggested that lakes at the tropics are unstable. The liquid in this region doesn’t last long before it evaporates and is carried by the atmospheric winds to the poles where it rains down to create the polar lakes. It’s strikingly similar to Earth’s water cycle.

Images of Titan at three wavelengths that probe the surface. The new study, written by Griffith et al, is published in Nature. Image Credit: Caitlin A. Griffith et al./Nature

But new data from the Cassini spacecraft’s visual and infrared mapping spectrometer changed that model. It found dark areas in Shangri-La suggesting substantial liquid ethane or methane lakes are present. One is roughly half the size of Utah’s Great Salt Lake and about 3 feet deep.

“We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought,” said Linda Spilker, the Cassini project scientist based at NASA’s Jet Propulsion Laboratory.

The tropical lakes ask more questions than they answer, namely where is the liquid for these lakes coming from?  “A likely supplier is an underground aquifer,” said Caitlin Griffith, a Cassini team associate at the University of Arizona. “In essence, Titan may have oases.

An artist's impression of a lake on smoggy Titan. Image Credit: NASA/JPL

If these lakes can be positively linked to subsurface methane stores, it will explain a lot about the moon’s methane cycle. In Titan’s atmosphere, ultraviolet light breaks apart methane to initiate a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane. “An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said.

Scientific interest in understanding the Titan’s methane cycle goes beyond an atmospheric curiosity. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life,” said Griffith. Understanding how the methane moves around the surface could help scientists pinpoint interesting areas in the search for life.

For now, we have yet to find any simple forms of life vacationing at Titan’s tropical lakes. Cassini still has multiple flybys of Titan planned, giving scientists more opportunities to get a good look at the mystery locked away under the moon’s atmosphere.

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