http://ciclops.org/view/5471/CASSINI_FINDS_HYDROCARBON_RAINS_MAY_FILL_TITAN_LAKES

MEDIA RELATIONS OFFICE
CASSINI IMAGING CENTRAL LABORATORY FOR OPERATIONS
(CICLOPS)
SPACE SCIENCE INSTITUTE, BOULDER, COLORADO
http://ciclops.org
media{at}ciclops.org 

Joe Mason (720) 974-5859
CICLOPS/Space Science Institute, Boulder, Colo.

Michael Buckley (240) 228-7536
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.

For Immediate Release: January 29, 2009

CASSINI FINDS HYDROCARBON RAINS MAY FILL TITAN LAKES

Recent images of Titan from NASA's Cassini spacecraft affirm the
presence of lakes of liquid hydrocarbons by capturing changes in the
lakes brought on by rainfall.

For several years, Cassini scientists have suspected that dark areas
near the north and south poles of Saturn's largest satellite might be
liquid-filled lakes. An analysis published today in the journal
Geophysical Research Letters of recent pictures of Titan's south polar
region reveals new lake features not seen in images of the same region
taken a year earlier. The presence of extensive cloud systems covering
the area in the intervening year suggests that the new lakes could be
the result of a large rainstorm and that some lakes may thus owe their
presence, size and distribution across Titan's surface to the moon's
weather and changing seasons.

The high-resolution cameras of Cassini's Imaging Science Subsystem
(ISS)
have now surveyed nearly all of Titan's surface at a global scale. An
updated Titan map, being released today by the Cassini Imaging Team,
includes the first near-infrared images of the leading hemisphere
portion of Titan's northern "lake district" captured on Aug. 15-16,
2008. (The leading hemisphere of a moon is that which always points in
the direction of motion as the moon orbits the planet.) These ISS
images
complement existing high-resolution data from Cassini's Visible and
Infrared Mapping Spectrometer (VIMS) and RADAR instruments.

Such observations have documented greater stores of liquid methane in
the northern hemisphere than in the southern hemisphere. And, as the
northern hemisphere moves toward summer, Cassini scientists predict
large convective cloud systems will form there and precipitation
greater
than that inferred in the south could further fill the northern lakes
with hydrocarbons.

Some of the north polar lakes are large. If full, Kraken Mare -- at
400,000 square kilometers -- would be almost five times the size of
North America's Lake Superior. All the north polar dark "lake" areas
observed by ISS total more than 510,000 square kilometers -- almost 40
percent larger than Earth's largest "lake," the Caspian Sea.

However, evaporation from these large surface reservoirs is not great
enough to replenish the methane lost from the atmosphere by rainfall
and
by the formation and eventual deposition on the surface of
methane-derived haze particles.

"A recent study suggested that there's not enough liquid methane on
Titan's surface to resupply the atmosphere over long geologic
timescales," said Dr. Elizabeth Turtle, Cassini imaging team associate
at the Johns Hopkins University Applied Physics Lab in Laurel, Md.,
and
lead author of today's publication. "Our new map provides more
coverage
of Titan's poles, but even if all of the features we see there were
filled with liquid methane, there's still not enough to sustain the
atmosphere for more than 10 million years."

Combined with previous analyses, the new observations suggest that
underground methane reservoirs must exist.

Titan is the only satellite in the solar system with a thick
atmosphere
in which a complex organic chemistry occurs. "It's unique," Turtle
said.
"How long Titan's atmosphere has existed or can continue to exist is
still an open question."

That question and others related to the moon's meteorology and its
seasonal cycles may be better explained by the distribution of liquids
on the surface. Scientists also are investigating why liquids collect
at
the poles rather than low latitudes, where dunes are common instead.

"Titan's tropics may be fairly dry because they only experience brief
episodes of rainfall in the spring and fall as peak sunlight shifts
between the hemispheres," said Dr. Tony DelGenio of NASA's Goddard
Institute for Space Studies in New York, a co-author and a member of
the
Cassini imaging team. "It will be interesting to find out whether or
not
clouds and temporary lakes form near the equator in the next few
years."

Titan and the transformations on its surface brought about by the
changing seasons will continue to be a major target of investigation
throughout Cassini's Equinox mission.

The Titan map and images of the lakes are available at:
http://ciclops.org, http://saturn.jpl.nasa.gov , and
http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory (JPL), a division of the California Institute of Technology
in Pasadena, manages the Cassini-Huygens mission for NASA's Science
Mission Directorate, Washington. The Cassini orbiter and its two
onboard
cameras were designed, developed and assembled at JPL. The imaging
team
consists of scientists from the U.S., England, France, and Germany.
The
imaging operations center and team leader (Dr. C. Porco) are based at
the Space Science Institute in Boulder, Colo. The Applied Physics
Laboratory, a division of Johns Hopkins University, meets critical
national challenges through the innovative application of science and
technology.

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