The Lakes of Titan

February 02, 2009

The lakes on Titan have changed shape, bolstering suspicions it is raining hydrocarbons on Saturn’s largest moon.

New images from the Cassini spacecraft, published in last week’s Geophysical Research Letters, show features in  lakes on Titan’s south polar region that were not present when Cassini flew by a year ago.

If scientists understand Titan’s cloud formations properly, the moon’s northern hemisphere is due for a deluge as summer approaches.

These mosaics of Titan's south polar region were made from images taken almost one year apart. In the images on the right, taken in 2005, new dark areas are visible (shown in circles.)  The very bright features are clouds in the lower atmosphere. The images were taken  infrared light. Resolution is several miles per pixel. Credit: NASA/Jet Propulsion Laboratory

Lake, ahoy!

July 30, 2008

While debate swirls about allocation, taxation and mitigation of Earth’s key energy source -- i.e. oil -- scientists have confirmed the location of a huge, untapped pool of liquid ethane and methane that’s your’s, mine and our’s for the taking.

It’s a bit far though. On a moon of Saturn.

Still, the discovery, announced in this week’s issue of the science research journal Nature, underscores a key reason for undertaking space exploration: so we can learn what’s out there.

What the dazzlingly brilliant and disciplined minds behind the Cassini science mission at Saturn have uncovered is that yes, indeed, Earth is not the only place in the universe that has liquids on its surface. Scientists have long suspected Titan had the goods, but it has taken years of detailed, methodical investigation to deliver the evidence.

Confirmation comes from a team at the University of Arizona charged with operating Cassini’s visual and infrared mapping spectrometer, which can ID chemicals by dissecting and analyzing wavelengths of light. VIMS found spectral fingerprints of liquid ethane pooled together in an area roughly 7,800 square miles (20,000 square km), which is just a bit bigger than Lake Ontario. Hence its name: Ontario Lacus.

Explains UA’s Robert Brown, the lead scientist for VIMS: "We know the lake is liquid because it reflects essentially no light at 5-micron wavelengths. It was hard for us to accept the fact that the feature was so black when we first saw it. 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."

Observations at 2-micron wavelengths apparently clinched the deal, when the signature of ethane appeared at the precise wavelength that ethane absorbs infrared light. Brown says tiny particles of ethane, small as cigarette smoke, are filtering out of the atmosphere and into the lake. Atmosphere ethane is made when ultraviolet light from the sun zaps methane molecules.

There’s more: Titan’s lake apparently is evaporating, as would be expected since its summer-time on Titan’s southern hemisphere, where the lake is located.

"We can see there's a shelf, a beach, that is being exposed as the lake evaporates," Brown said.

The beach is darker than the shoreline, indicating that it is wet with organics or covered with a thin layer of liquid organics. Scientists know what’s not there: water ice, ammonia, ammonia hydrate or carbon dioxide. And it’s cold -- about 290 below zero Fahrenheit. That’s why the hydrocarbons are in a liquid state, not gas.

Personally, but I don’t mind the extra charge to Uncle Sam’s credit card to keep Cassini flying. Takes the edge off all the other mindless stuff.