Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Image Credit: NASA/JPL-Caltech/Space Science Institute
Although you wouldn’t want to go fishing here, Saturn’s moon Titan shows evidence of a methane lake in its tropical zone. Estimated to be about one metre deep, the non-toxic “puddle” appears about half the size of Utah’s Great Salt Lake.
This was unexpected. Scientists had theorized that long-standing bodies of this liquefied, colorless, odorless substance should only be found at the poles. So where did it come from? “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”
Why is this new Cassini finding significant? By understanding how lakes and other standing bodies of liquids form on Titan’s surface helps scientists to understand more about this Saturnian satellite’s weather patterns. Similar to Earth’s water recycling patterns, Titan has a methane cycle. Its atmosphere refracts ultraviolet light which breaks methane apart and triggers a complex chain of chemical reactions. However, current models haven’t quite been able to pinpoint the abundance of methane which creates liquid bodies.
Titan shown in ultraviolet and infrared wavelengths. Photo captured by the Cassini spacecraft (Photo credit: Wikipedia)
“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”
By creating a global circulation model, researchers have attempted to explain this phenomenon. They theorize liquid methane evaporates in the equatorial regions and is transported to the poles via winds.
Here cooler temperatures cause this greenhouse gas to condense and return to the surface in the form of polar lakes. Through the use of Cassini’s visual and infrared mapping, they have spotted dark markings in the tropical region known as Shangri-La, near the spot where the European Space Agency’s Huygens probe landed in 2005.
When the probe landed, its lamp vaporized localized methane – evidence that it may have landed in a condensed area. Dark visual images appear on mapping taken by the infrared spectrometer where liquid methane and ethane occur and need not be deep to be detected.
While Cassini’s radar mapper has found dark regions in the polar areas, this is the first where it has captured evidence of lakes at lower latitudes.
The Casinni team has been careful in its research. The tropical lakes aren’t a recent find and have been studied since 2004 when detected by the infrared mapping spectrometer. During this time there has been only one “rain shower” recorded, so researchers are confident the lakes aren’t fed by evaporation and falling of methane rain.
“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, Pasadena, Calif. “Cassini still has multiple opportunities to fly by this moon going forward, so we can’t wait to see how the details of this story fill out.”
Original Story Source: JPL/NASA News Release.
