Cassini Finds Titan's Clouds Hang on to Summer

[nansy]

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.

 

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.