New data from NASA’s Cassini spacecraft shows that a shift in seasonal sunlight has resulted in an abrupt, wholesale reversal in the circulation of the atmosphere of Saturn’s moon Titan. According to researchers, the data shows “definitive” evidence for sinking air at the moon’s south pole where previously the air was upwelling. A paper on the data published today in the journal Nature states that the “key” to air circulation in Titan’s atmosphere is the moon’s tilt in relation to the sun.

“Cassini’s up-close observations are likely the only ones we’ll have in our lifetime of a transition like this in action,” said Nick Teanby, the study’s lead author and a Cassini team associated at the University of Bristol. “It’s extremely exciting to see such rapid changes on a body that usually changes so slowly and has a ‘year’ that is the equivalent of nearly 30 Earth years.”

Titan is interesting to researchers because is is one of only a few objects in our solar system, along with Earth, Venus, and Mars, that has both a solid surface and substantial atmosphere. Models of Titan’s atmosphere have predicted atmosphere circulation changes for almost 20 years, but the Titan pole that is currently undergoing winter is normally pointed away from Earth. Cassini is finally observing the circulation changes directly.

“Understanding Titan’s atmosphere gives us clues for understanding our own complex atmosphere,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory. “Some of the complexity in both places arises from the interplay of atmospheric circulation and chemistry.”

NASA also stated that Cassini has detected complex chemical production in Titan’s atmosphere at up to 600 kilometers (400 miles) above the moon’s surface. This means that atmospheric circulation extends to about 100 kilometers (60 miles) higher than scientists expected. The compression of that air as it sank lower created a “hot spot” high above Titan’s south pole. That suggested that changes would be coming to the moon’s atmosphere, and that a layer of haze first detected by NASA’s Voyager spacecraft may not be as “detached” as was previously thought. The haze, instead, may be where small haze particles combine into larger aggregates that drop in Titan’s atmosphere and give the moon it’s orange color.

“Next, we would expect to see the vortex over the south pole build up,” said Mike Flasar, Cassini’s composite infrared spectrometer principal investigator at NASA’s Goddard Space Flight Center. “As that happens, one question is whether the south winter pole will be the identical twin of the north winter pole, or will it have a distinct personality? The most important thing is to be able to keep watching as these changes happen.”

(Image courtesy ESA)