Icy Cloud on Titan Marks Change of Seasons: 'Winter is Coming' on Saturn's Moon

The turn of seasons doesn't only affect Earth. It also affects Titan, Saturn's largest moon. Researchers have witnessed a massive ice cloud taking shape over the moon's south pole, the latest sign that the change of seasons is setting off a cascade of radical adjustments across the surface of Titan.

The latest findings were made with the Composite Infrared Spectrometer (CIRS) on NASA's Cassini spacecraft. Using the far infrared part of the light spectrum, scientists were able to view the southern ice cloud.

This cloud wasn't always at the south pole, though. It was first created as warm air from the southern hemisphere rose high into the atmosphere and was then transported to the cold north pole. The air then cooled and sank down to the lower layers of the atmosphere, where it formed ice clouds. A similar phenomenon can be seen on Earth, called a Hadley cell, when warm, moist air is carried from the tropics to the cooler middle latitudes.

Yet this new southern ice cloud reveals that an important pattern of global air circulation on Titan has actually reversed direction. Instead of the north pole, it seems that the air has travelled to the south pole. Researchers have long expected this reversal--it occurs during the change of seasons. The official transition from winter to spring at Titan's north pole occurred in August 2009; because each of the moon's seasons lasts for about seven and a half Earth years, though, it's only now that the reversal is taking place.

"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," said Carrie Anderson, a CIRS team member, in a news release.

It seems that the southern ice cloud is building rapidly as the seasons change. The northern ice cloud, in contrast, is slowly fading away.  Currently, researchers are still attempting to find out exactly what these clouds are composed of, though they have already ruled out simple chemicals such as methane, ethane and hydrogen cyanide.

The cloud formation doesn't only tell researchers more about Titan, though. It could also have implications for Earth. What is currently happening at Titan's poles has some analogy to our planet and its ozone holes. More specifically, the ices in the high polar clouds on Earth play a role in releasing the chlorine that destroys ozone. Understanding how this affects Titan's chemistry could, in turn, tell researchers a bit more about Earth.