BY DR EMILY BALDWIN
Posted: 5 June, 2009
A three-and-a-half year study of over 200 clouds in Titan’s dense atmosphere reveals their formation and movement to be somewhat out of synch with the moon’s seasons.
The study was conducted between July 2004 and December 2007 using data from NASA’s Cassini mission. While the clouds follow the predicted global circulation models, they are slightly out of synch with the seasons, with clouds still lingering in the southern hemisphere as fall fast approaches.
This infrared image of Saturn's moon Titan shows a large burst of clouds in the moon's south polar region. These clouds form and move much like those on Earth, but in a much slower, more lingering fashion. Image: NASA/JPL/University of Arizona/University of Nantes.
“Titan’s clouds don’t move with the seasons exactly as we expected,” says 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.”
Abnormally warm autumns occur on the Earth when low pressure systems are blocked in the winter hemisphere. By contrast, scientists think that the unexpectedly warm and wet - and therefore cloudy - summer on Titan could be the result of sluggish temperature changes at the surface.
As the equinox approaches in August 2009, so summer on Titan morphs into fall, and the moon’s clouds are expected to disappear altogether. Circulation models, however, predicted that the southern latitude clouds should have started to fade out since 2005, but Cassini spotted clouds at these locations well into 2007, with particularly active systems at mid-latitudes and the equator.
Since Titan is the only moon in our Solar System with a substantial atmosphere, it shares important similarities to the Earth’s own weather system, but also significant differences. Titan’s dense, nitrogen-methane atmosphere responds much more slowly than Earth’s atmosphere, as it receives about 100 times less sunlight due to its greater distance from our warmth-giving star. Furthermore, seasons on Titan last more than seven Earth years.
Scientists will continue to observe the long-term changes in Titan's atmosphere during Cassini’s extended mission, which runs until the fall of 2010.