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October
12, 2007: Newly assembled radar images from the Cassini
spacecraft are giving researchers their best-ever view of
hydrocarbon lakes and seas on the north pole of Saturn's moon
Titan, while a new radar image reveals that Titan's south
pole also has lakes.
Approximately
60 percent of Titan's north polar region (north of 60o
latitude) has been mapped by Cassini's radar. About 14 percent
of the mapped region is covered by what scientists believe
are lakes filled with liquid methane and ethane:
Above:
A false-color mosaic of Titan's north pole. [More]
The
mosaic image was created by stitching together radar images
from seven Titan flybys over the last year and a half. At
least one of the pictured lakes is larger than Lake Superior.
"This
is our version of mapping Alaska, the northern parts of Canada,
Greenland, Scandinavia and Northern Russia," says Rosaly
Lopes, Cassini radar scientist at NASA's Jet Propulsion Laboratory.
"It's like mapping these regions of Earth for the first
time."
Lakes
and seas are very common at Titan's high northern latitudes
where winter is now underway. Scientists say it
rains methane and ethane there, filling the lakes and
seas. These liquids also carve meandering rivers and channels
on the moon's surface.
Now
Cassini is moving into unknown territory: the south pole of
Titan. On Oct. 2, the spacecraft excecuted a flyby in which
a prime goal was the hunt for southern lakes. Lopes explains:
"We wanted to see if there are more lakes present there
and, sure enough, there they are, three little lakes smiling
back at us."
Above:
Two of three newfound lakes near Titan's south pole. [More]
"Titan
is indeed the land of lakes and seas," she adds. "It
will be interesting to see the differences between the north
and south polar regions." It
is now summer at Titan's south pole. A season on Titan lasts
nearly 7.5 years, one quarter of a Saturn year, which is 29.5
years long. Monitoring seasonal changes in the lakes will
help scientists understand the processes at work there.
They
are already making progress in understanding how the lakes
may have formed. On Earth, lakes fill low spots or are created
when the local topography intersects a groundwater table.
Lopes and her colleagues think that the depressions containing
the lakes on Titan may have formed by volcanism or by a type
of "karstic erosion" which leaves a depression where
liquids can accumulate. Karstic
lakes are common on Earth. For example, in parts of Minnesota
and central Florida there are hundreds of such lakes.
"The
lakes we are observing on Titan appear to be in varying states
of fullness, suggesting their involvement in a complex hydrologic
system akin to Earth's water cycle. This makes Titan unique
among the extra-terrestrial bodies in our solar system,"
says Alex Hayes, a graduate student who studies Cassini radar
data at the California Institute of Technology in Pasadena.
"The
lakes we have seen so far vary in size from the smallest observable,
approximately 1 square kilometer, to greater than 100,000
square kilometers, which is slightly larger than the Great
Lakes in the Midwestern U.S.," Hayes says. "Of the
roughly 400 observed lakes, 70 percent of their area is taken
up by 'seas' greater than 26,000 square kilometers."
Future
radar flybys will map terrain even closer to the south pole.
Stay tuned for more lakes!
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Editor: Dr.
Tony Phillips | Credit: Science@NASA
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