Ice clouds on Titan signal start of seven year autumn on south pole of Saturn's largest moon

A seven-year autumn has begun on the south pole of Saturn's largest moon, scientists believe.

An ice cloud made from an unknown material taking shape over Titan’s south pole has led experts to deem that an important pattern of global air circulation on the moon has reversed direction, The Daily Mail reports.

The same type of cloud has been hanging over Titan's north pole, but it is now fading and spring has arrived there, according to observations made by an infrared spectrometer on NASA's Cassini craft.

‘We associate this particular kind of ice cloud with winter weather on Titan, and this is the first time we have detected it anywhere but the north pole,’ NASA spokesman Donald Jennings said.

Cassini first observed the circulation pattern when warm air from the south was rising high in the atmosphere and getting transported to the cold north, where it cooled down and formed ice clouds.

Experts had long expected a reversal of this circulation when Titan's north pole began to get hotter and its south pole started to cool down. The official transition in the north happened in August 2009.
But with each season on the moon lasting around seven-and-a-half earth years, researchers were still unsure when the reversal would happen and how long it would take.

However the first signs of a reversal appeared in data early last year, which showed the southern autumn was beginning and a swirling polar vortex could be seen at the south pole.

Despite this new activity the southern ice cloud was yet to appear, but it was eventually spotted in July 2012, according to a study published in Astrophysical Journal Letters in December last year.

Cassini participating scientist Carrie Anderson said: ‘This lag makes sense, because first the new circulation pattern has to bring loads and loads of gases to the south pole.
'Then the air has to sink. The ices have to condense. And the pole has to be under enough shadow to protect the vapors that condense to form those ices.’

F. Michael Flasar of NASA added: ‘What's happening at Titan's poles has some analogy to Earth and to our ozone holes. And on Earth, the ices in the high polar clouds aren't just window dressing.
‘They play a role in releasing the chlorine that destroys ozone. How this affects Titan chemistry is still unknown. So it's important to learn as much as we can about this phenomenon, wherever we find it.’