Lakes Found on Saturn's Moon Titan
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NASA's Cassini spacecraft has found lakes on Saturn's moon Titan.
The lakes are most likely the source of hydrocarbon smog in the frigid moon's
atmosphere. Finding the source of the complex soup of hydrocarbons in
Titan's atmosphere has been a major goal for the Cassini mission and is a
significant accomplishment.
Numerous well-defined dark patches resembling lakes are present in radar
images of Titan's high latitudes. At Titan's frigid temperatures, about minus
180 degrees Celsius, the liquids in the lakes are most likely methane or a
combination of methane and ethane.
"This is a big deal," said Steve Wall, deputy radar team leader at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "We've now seen a place other than
Earth where lakes are present."
This area of Titan has been in winter's shadow since before Cassini arrived,
and the spacecraft had not flown over it before. During the flyby, Cassini's
radar spotted several dozen lakes as small as 0.6 miles wide, with some
nearly 20 miles wide. The biggest lake is about 62 miles long and may be
only partly wet.
"What we see is darker than anything we've ever seen elsewhere on Titan. It
was almost as though someone laid a bull's-eye around the whole north pole
of Titan, and Cassini sees these regions of lakes just like those we see on
Earth," said Larry Soderblom, Cassini interdisciplinary scientist at the U.S.
Geological Survey, Flagstaff, Ariz. "Titan has turned out to be like a musical
crescendo -- each pass is more exciting than the last."
Titan has not yielded its secrets easily because the dense smoggy
atmosphere makes it very difficult to obtain good visible images. Radar can
penetrate the smog and obtain clear images.
Dark regions in radar images generally mean smoother terrain, while bright
regions mean a rougher surface. Some of the new radar images show
channels leading in or out of a variety of dark patches. The shape of the
channels also strongly implies they were carved by liquid.
Some of the dark patches and connecting channels are completely black --
they reflect back essentially no radar signal, which means they must be
extremely smooth and might contain liquid. In some cases rims can be seen
around the dark patches, suggesting deposits that might form as liquid
evaporates.
Scientists had predicted, but had no confirmation until now, that pools of liquid
were contributing to the high concentration of methane and other
hydrocarbons in Titan's atmosphere.
"We've always believed Titan's methane had to be maintained by liquid lakes
or extensive underground 'methanofers,' the methane equivalent of aquifers.
We can't see methanofers but we can now say we've seen lakes," said
Jonathan Lunine, Cassini interdisciplinary scientist at the University of
Arizona, Tucson.
Since lakes come and go with the seasons, they wax and wane over time.
Winds might alter the roughness of their surfaces. Repeat coverage of these
areas is expected to provide more information on these lakes. By passing
over a lake in a different direction, Cassini may see the effect of prevailing
winds in the changing brightness of the lake surface. On later passes toward
the end of its prime mission, Cassini might see changes in the shape or size
of lakes as winter yields to spring in the northern hemisphere.
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