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NASA Confirms Liquid Lake on Saturn Moon

Written by thomas · Filed Under Aeronautics News 

July 30, 2008

thomas

PASADENA, Calif., July 30 /PRNewswire-USNewswire/ — NASA scientists
have concluded that at least one of the large lakes observed on Saturn’s
moon Titan contains liquid hydrocarbons, and have positively identified the
presence of ethane. This makes Titan the only body in our solar system
beyond Earth known to have liquid on its surface.

Scientists made the discovery using data from an instrument aboard the
Cassini spacecraft. The instrument identified chemically different
materials based on the way they absorb and reflect infrared light. Before
Cassini, scientists thought Titan would have global oceans of methane,
ethane and other light hydrocarbons. More than 40 close flybys of Titan by
Cassini show no such global oceans exist, but hundreds of dark lake-like
features are present. Until now, it was not known whether these features
were liquid or simply dark, solid material.

“This is the first observation that really pins down that Titan has a
surface lake filled with liquid,” said Bob Brown of the University of
Arizona, Tucson. Brown is the team leader of Cassini’s visual and mapping
instrument. The results will be published in the July 31 issue of the
journal Nature.

Ethane and several other simple hydrocarbons have been identified in
Titan’s atmosphere, which consists of 95 percent nitrogen, with methane
making up the other 5 percent. Ethane and other hydrocarbons are products
from atmospheric chemistry caused by the breakdown of methane by sunlight.

Some of the hydrocarbons react further and form fine aerosol particles.
All of these things in Titan’s atmosphere make detecting and identifying
materials on the surface difficult, because these particles form a
ubiquitous hydrocarbon haze that hinders the view. Liquid ethane was
identified using a technique that removed the interference from the
atmospheric hydrocarbons.

The visual and mapping instrument observed a lake, Ontario Lacus, in
Titan’s south polar region during a close Cassini flyby in December 2007.
The lake is roughly 7,800 square miles in area, slightly larger than North
America’s Lake Ontario.

“Detection of liquid ethane confirms a long-held idea that lakes and
seas filled with methane and ethane exist on Titan,” said Larry Soderblom,
a Cassini interdisciplinary scientist with the U.S. Geological Survey in
Flagstaff, Ariz. “The fact we could detect the ethane spectral signatures
of the lake even when it was so dimly illuminated, and at a slanted viewing
path through Titan’s atmosphere, raises expectations for exciting future
lake discoveries by our instrument.”

The ethane is in a liquid solution with methane, other hydrocarbons and
nitrogen. At Titan’s surface temperatures, approximately 300 degrees
Fahrenheit below zero, these substances can exist as both liquid and gas.
Titan shows overwhelming evidence of evaporation, rain, and fluid-carved
channels draining into what, in this case, is a liquid hydrocarbon lake.

Earth has a hydrological cycle based on water and Titan has a cycle
based on methane. Scientists ruled out the presence of water ice, ammonia,
ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also
suggest the lake is evaporating. It is ringed by a dark beach, where the
black lake merges with the bright shoreline. Cassini also observed a shelf
and beach being exposed as the lake evaporates.

“During the next few years, the vast array of lakes and seas on Titan’s
north pole mapped with Cassini’s radar instrument will emerge from polar
darkness into sunlight, giving the infrared instrument rich opportunities
to watch for seasonal changes of Titan’s lakes,” Soderblom said.

Launched in Oct. 1997, Cassini’s 12 instruments have returned a daily
stream of data from Saturn’s system. The mission is a cooperative project
of NASA, the European Space Agency and the Italian Space Agency.

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