Cassini Finds Titan's Clouds Hang on to Summer

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DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov

IMAGE ADVISORY: 2009-093 June 3, 2009

Cassini Finds Titan's Clouds Hang on to Summer

Cloud chasers studying Saturn's moon Titan say its clouds form and move much like those on
Earth, but in a much slower, more lingering fashion.

Their forecast for Titan's early autumn -- warm and wetter.

Scientists with NASA's Cassini mission have monitored Titan's atmosphere for three-and-a-half
years, between July 2004 and December 2007, and observed more than 200 clouds. They found
that the way these clouds are distributed around Titan matches scientists' global circulation
models. The only exception is timing -- clouds are still noticeable in the southern hemisphere
while fall is approaching.

"Titan's clouds don't move with the seasons exactly as we expected," said Sebastien Rodriguez
of the University of Paris Diderot, in collaboration with Cassini visual and infrared mapping
spectrometer team members at the University of Nantes, France. "We see lots of clouds during
the summer in the southern hemisphere, and this summer weather seems to last into the early fall.
It looks like Indian summer on Earth, even if the mechanisms are radically different on Titan
from those on Earth. Titan may then experience a warmer and wetter early autumn than
forecasted by the models."

On Earth, abnormally warm, dry weather periods in late autumn occur when low-pressure
systems are blocked in the winter hemisphere. By contrast, scientists think the sluggishness of
temperature changes at the surface and low atmosphere on Titan may be responsible for its
unexpected warm and wet, hence cloudy, late summer.

The new infrared images showing the global cloud pattern are now available at:
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

As summer changes to fall at the equinox in August 2009, Titan's clouds are expected to
disappear altogether. But, circulation models of Titan's weather and climate predict that clouds
at the southern latitudes don't wait for the equinox and should have already faded out since
2005. However, Cassini was still able to see clouds at these places late in 2007, and some of
them are particularly active at mid-latitudes and the equator.

Titan is the only moon in our solar system with a substantial atmosphere, and its climate shares
Earth-like characteristics. Titan's dense, nitrogen-methane atmosphere responds much more
slowly than Earth's atmosphere, as it receives about 100 times less sunlight because it is 10 times
farther from the sun. Seasons on Titan last more than seven Earth years.

Scientists will continue to observe the long-term changes during Cassini's extended mission,
which runs until the fall of 2010. Cassini is set to fly by Titan on May 5.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and
the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Cassini-Huygens mission for NASA's Science Mission Directorate. The Cassini orbiter was
designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team
is based at the University of Arizona.

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