Titan's Giant Methane Sea is Eerily Calm

Because of its Earth-like weather system, astronomers use Saturn's moon Titan as a model for studying the early history of Earth. A new revelation that the moon's second largest sea, Ligeia Mare, is eerily placid - perhaps as smooth as a mirror's surface - has led scientist to theorize that a lack of surface winds is responsible for the smoothness. The report offers new insights into the weather patterns on the distant moon.

"If you could look out on this sea, it would be really still. It would just be a totally glassy surface," said Howard Zebker, a professor of geophysics and electrical engineering at Stanford University.

Writing in the journal Geophysical Research Letters, Zebker and his colleagues, report on the windless sea and offer new theories about the moon's ecosystem.

"Titan is the best analog that we have in the solar system to a body like the Earth because it is the only other body that we know of that has a complex cycle of solid, liquid, and gas constituents," Zebker said.

Titian has a planet-like atmosphere large seas. Measuring at roughly 260 miles (420 km) by 217 miles (350 km), Ligeia Mare is larger than Lake Superior on Earth, but instead of fresh water, the sea is filled with liquid methane and ethane.

Scientist use radar data from NASA's Saturn-orbiting Cassini spacecraft to gather the images of Titan's smooth sea. By bouncing radio waves off the sea's surface and analyzing the echo, scientists can get an idea of how much wave action is going on at sea.

 "If the lake were really flat, it would act as a perfect mirror and you would have an extremely bright image of the sun," Zebker said. "But if you ruffle up the surface of the sea, the light gets scattered in a lot of directions, and the reflection would be much dimmer. We did the same thing with radar on Titan."

This imaging method has revealed an eerily placid Ligeia Mare.

 "Cassini's radar sensitivity in this experiment is one millimeter, so that means if there are waves on Ligeia Mare, they're smaller than one millimeter. That's really, really smooth," Zebker said.

Possible explanations for this include that it just happened to not be windy when the data was collected, resulting in what appears as a smooth sea. Another possibility is that the surface of the lake is coated with a thin layer of material that suppresses surface action. "For example, on Earth, if you put oil on top of a sea, you suppress a lot of small waves," Zebker said.

The analysis also confirmed that the terrain around Ligeia Mare is composed of solid organic material, likely the same methane and ethane that make up the sea.

"Like water on Earth, methane on Titan can exists as a solid, a liquid, and a gas all at once," Zebker said.

Titan is different in the details from Earth, but because there is global circulation happening, the big picture is the same," Zebker added. "Seeing something in two very different environments could help reveal the overall guiding principles for the evolution of planetary bodies, and help explain why Earth developed life and Titan didn't."