The Lagoons of Titan: Oily Liquid Confirmed on Saturn Moon

By Alexis Madrigal

Earthlings might be scrambling to find liquid hydrocarbons buried in our planet, but Saturn's moon Titan has plenty to spare.

Scientists say that a dark, smooth surface feature spotted on the moon last year is definitely a lake filled primarily with liquid ethane, a simple hydrocarbon.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid," said the paper's lead author, University of Arizona professor Robert Brown.

The new observations affirm that Titan is one of the likeliest places to look for life in our solar system. Some astrobiologists have speculated that life could develop in the moon's hydrocarbon lakes, although it would have to be substantially different from known life on Earth, which requires liquid water.

Mixed in solution with the ethane, the lake is also believed to contain nitrogen, methane, and a variety of other simple hydrocarbons.

The Cassini-Huygens probe determined the chemical composition of the liquid by the way it reflected light, a technique known as spectrometry that has provided most of our knowledge about other planets' atmospheric compositions.

"It was hard for us to accept the fact that the feature was so black when we first saw it," Brown said. "More than 99.9 percent of the light that reaches the lake never gets out again. For it to be that dark, the surface has to be extremely quiescent, mirror smooth. No naturally produced solid could be that smooth."

Further, the scientists saw the specific absorption signature of ethane, which absorbs light at exactly 2-micron wavelengths.

These kinds of measurements are made more difficult by the hydrocarbon haze that engulfs the moon, making it hard to actually see the Titanic ground. Cassini scientists have to take advantage of narrow observation windows. One of these occurred in December 2007, which allowed them to catch this view of the lake, Ontario Lacus. At 7,800 square miles, it's slightly larger than the Earthbound Lake Ontario

Ethane is the byproduct of a solar-energy-induced reaction that transforms atmospheric methane, aka natural gas. Scientists believe ultrafine particles of ethane fall from the atmosphere to the surface and fill the lake.

Here on earth, ethane is used to create ethylene, which is used as an all-purpose chemical precursor and is the world's most-produced organic compound.

Brown and his team will publish their results in the July 31 issue of the journal Nature.

Image: Courtesy NASA. Ontario Lacus, which translates roughly to "Bigfoot track on Saturnian moon."

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