NASA's Cassini probe has spotted a vast vortex over the south pole of Saturn's moon Titan, triggered by the moon's move into winter.
"The structure inside the vortex is reminiscent of the open cellular convection that is often seen over Earth's oceans," says Tony Del Genio of NASA's Goddard Institute for Space Studies.
"But, unlike on Earth, where such layers are just above the surface, this one is at very high altitude - maybe a response of Titan's stratosphere to seasonal cooling as southern winter approaches. But so soon in the game, we’re not sure."
When Cassini first arrived in the Saturn system in 2004, one of the first things it saw was a 'hood' of high-altitude haze and a vortex over Titan’s north pole.
While this hood is still there, the circulation in the upper atmosphere has been moving from the illuminated north pole to the cooling south pole, causing down-wellings over the south pole, haze and the formation of the vortex.
Cassini’s visible light cameras saw the first signs of hazes starting to concentrate over Titan’s south pole in March.
"[Cassini's visual and infrared mapping spectrometer] VIMS has seen a concentration of aerosols forming about 200 miles above the surface of Titan's south pole," says Christophe Sotin of NASA's Jet Propulsion Laboratory. "We've never seen aerosols here at this level before, so we know this is something new."