A NASA spacecraft has spied a vortex swirling in the atmosphere high above the south pole of the Saturn moon Titan, hinting that winter may be coming to the huge body's southern reaches.

NASA's Cassini probe photographed the polar vortex — or mass of swirling gas — during a flyby of Titan on June 27. The vortex appears to complete one full rotation in nine hours, while it takes Titan about 16 days to spin once around its axis.

"The structure inside the vortex is reminiscent of the open cellular convection that is often seen over Earth's oceans," Tony Del Genio, a Cassini team member at NASA's Goddard Institute for Space Studies in New York, said in a statement.

"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," he added. "But so soon in the game, we're not sure." [Gallery: Amazing Titan Photos]