Huge Lake of Hydrocarbon Studied on Saturn's Titan

A giant, glassy lake larger than North America's Lake Ontario graces the south pole of Saturn's largest moon Titan, according to research from the University of Arizona's Lunar and Planetary Laboratory. Titan, which is one-and-a-half times the size of Earth's moon and bigger than either Mercury or Pluto, is one of the most intriguing bodies in the solar system when it comes to exploring environments that may give rise to life.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid,"reported lead researcher Robert Brown of the University of Arizona in late July, 2008.  The lake which covers 20,000 square kilometers is filled mostly with methane and ethane, hydrocarbons that are gases on Earth but liquid on the bone-freezing surface of Titan -the only solar system moon known to support a planet-like atmosphere.

More recent research shows that Titan may have a subterranean ocean of hydrocarbons and some topsy-turvy topography in which the summits of its mountains lie lower than its average surface elevation.

Titan is also more squashed in its overall shape—like a rubber ball pressed down by a foot—than researchers had expected, said Howard Zebker, a Stanford geophysicist and electrical engineer involved in the work. The new findings may help explain the presence of large lakes of hydrocarbons at both of Titan's poles, which have been puzzling researchers since being discovered in 2007.

"Since the poles are squished in with respect to the equator, if there is a hydrocarbon 'water table' that is more or less spherical in shape, then the poles would be closer down to that water table and depressions at the poles would fill up with liquid," Zebker said. The shape of the water table would be controlled by the gravitational field of Titan, which is still not fully understood.

Hydrocarbons are the only materials on Titan's surface that would remain liquid at minus180 degrees Celsius, the average temperature of the moon's surface. Any water would be frozen, making it plausible that instead of groundwater, Titan would have the equivalent in hydrocarbons.

Zebker, the lead author, and a group of colleagues have been making radar measurements of Titan's surface over the last four years using an instrument aboard the Cassini spacecraft, which is orbiting Saturn. Whenever Cassini passes close enough, they sweep beams of cloud-penetrating radar through Titan's thick atmosphere and across the surface. Using the radar data, they can calculate the surface elevations along the tracks of the sweep.

Before the imaging of the Cassini mission, astronomers thought Titan was covered in a global ocean, though the spacecraft's flybys of the moon debunked notion. Using an instrument on NASA's Cassini orbiter, they discovered that a lake-like feature in the south polar region of Saturn's moon, Titan, is truly wet. The lake is about 235 kilometers, or 150 miles, long. Evidence for features similar to Earth's lakes and seas, along with telltale signs of erosion from flowing water, have come to light.

Possible evidence for lake-like features came from radar images, but this method can't distinguish between liquid and very fine gravel or other tiny solids, Brown explained.

"Detection of liquid ethane in Ontario Lacus confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan," said researcher Larry Soderblom of the U.S. Geological Survey in Flagstaff, Ariz.

Soderblom, Brown and their colleagues used the infrared abilities of Cassini's visual and infrared mapping spectrometer, or VIMS, to peer through Titan's hazy veil of hydrocarbons that extends more than 620 miles (1,000 km) above the moon's surface. Only part of the lake is visible on Titan's sunlit side. What appears to be a 'beach' is seen in the lower right of the image, below the bright lake shoreline.

When VIMS observed the lake, named Ontario Lacus, it detected ethane, a simple hydrocarbon that Titan experts have long been searching for. The ethane is in liquid solution with methane, nitrogen and other low-molecular weight hydrocarbons.

The ubiquitous hydrocarbon haze in Titan's atmosphere hinders the view to Titan's surface. But there are transparent atmospheric "windows" at certain infrared light wavelengths through which Cassini's VIMS can see to the ground. VIMS observed Ontario Lacus on Cassini's 38th close flyby of Titan in December 2007.

Infrared spectroscopy doesn't tell the researchers how deep the lake is, other than it must be at least a centimeter or two, or about three-quarters of an inch, deep.

"We know the lake is liquid because it reflects essentially no light at 5-micron wavelengths," Brown said. "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."

VIMS observations at 2-micron wavelengths shows the lake holds ethane. The scientists saw the specific signature of ethane as a dip at the precise wavelength that ethane absorbs infrared light. Tiny ethane particles almost as fine as cigarette smoke are apparently filtering out of the atmosphere and into the lake, Brown said.

Ethane is a simple hydrocarbon produced when ultraviolet light from the sun breaks up its parent molecule, methane, in Titan's methane-rich, mostly nitrogen atmosphere.

Before the Cassini mission, several scientists thought that Titan would be awash in global oceans of ethane and other light hydrocarbons, the byproducts of photolysis, or the action of ultraviolet light on methane over 4.5 billion years of solar system history. But 40 close flybys of Titan by the Cassini spacecraft show no such oceans exist.

The observations also suggest the lake is evaporating. The lake is ringed by a dark beach, where the black lake merges with the bright shoreline.

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

That the beach is darker than the shoreline could mean that the "sand" on the beach is wet with organics, or it could be covered with a thin layer of liquid organics, he said.

The VIMS measurements rule out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The VIMS result gives researchers new insight on Titan's chemistry and weather dynamics.

Cassini cameras and radar and the UA-built camera aboard the European Space Agency's Huygens probe that landed on Titan in January 2005 have shown that methane saturates and drains from Titan's atmosphere, creating river-like and lake-like features on the surface. Just as water cycles through the hydrologic regime on Earth, methane cycles through a methanological cycle on Titan.

The Cassini mission is an international cooperative effort of NASA, the European Space Agency (ESA), Italian Space Agency (ASI) and several separate European academic and industrial contributors.

Posted by Casey Kazan.

Source Link:

http://uanews.org/node/20615

Comments

[Daniel]

Why, when the article says it's bigger than Lake Ontario do you depict an image comparing it to Lake Superior?

[knoxvilledaniel]

This sounds like prime beach - front property on Titan, a VERY good place to land a future space probe. There's no telling WHAT we might find there. A possible primordial Earth - like environment ?

[cristian]

lol Daniel.

[EvilCosmicMonkeyfrom Knoxville]

NASA, JPL, et al, has to stick a crowbar in its checkbook & free up some $$$ for a probe to send to that lake. How's about a submersible rather than landing a probe close to it ?

This is doable.

[claudio]

It has been said and repeated by quite few scientists that Titan resemble what the Earth was hundreds Millions or billions of Y agò.

This is completely WRONG...............these scientists should go back to school.

The Earth was always very near to the Sun (basically 1 AU) while the moon of Saturn is at say 11 AU.

No heat from the sun would it make resembling earth....never.

Titan holds an atmosphere of methane for some 95% and additional hydrocarbons - Ammonia and other for the remaining 5%....and when it rains the methane comes down and becomes liquid at surface temperature of -180°C....and may very well form lakes of liquid methane.

NO life forms are believed to exist on Titan...NONE of any kind.

Totally dissimilar to earth ever.

The methane in the ATM is a powerful 'house flower gas' but considering the very low sun heat the temperature is extremely cold.

How and in what Titan resembles earth and can help understanding on how the earth was hundreds millions Y agò ???????????

The simple fact that pushed NASA and ESA to go to Titan were the images of Voyager that showed clearly an ATM there....tell these new-joung 'scientists'.

Titan , aside from any declaration of the so called scientists...is 'another world' ...as intereting as Venus can be...both being deadly bodies...the one too cold and with a Hydrocarbon and ammonia based ATM and the other plenty of Sulfur-acid ATM and extremely high surface temperature...and pressure.

Both unlivable and rather difficult to explore in depth....even from robotized units...and then Why to spend additional money for Titan ith another mission ???

The Cassini-Huygens mission was expensive enough for us European and for You americans.

What else to say ??

Look at Europa...or similar moons....much smarter missions...even Mars is smarter than spending money for Titan.

Regards to the Tax Payers.

[Mifkin]

Claudio I believe its "Earth-Like" minues 200 degrees.

All the geological processes are fairly similar and water acts like it does here on Earth, just 200 degress colder, would be interesting to see what type of lifeform could survive in that.

[Brad]

Claudio has some very valid points, but exploration should pick up on the moon and not deminish. If we could replicate the way Titan produces these hydrocarbons from the Atmospheric methane (natualy occuring without biologic interjection) we could in theory create hydrocarbons that could take over oil use. Creating a renewable atlernate fuel.