Cassini Spots Swirling, Toxic Cloud at Titan's South Pole as Seasons Change

NASA's Cassini mission continues to reveal new insights when it comes to Saturn's moon, Titan. Now, the mission has revealed that a giant, toxic cloud is hovering over the south pole of the large moon after the atmosphere there cooled dramatically.

"The discovery suggests that the atmosphere of Titan's southern hemisphere is cooling much faster than we expected," said Remco de Kok, lead author of the new study, in a news release.

Titan is the only moon in our solar system that is cloaked in a dense atmosphere. Like Earth, it experiences seasons as it orbits around Saturn. Each season lasts about seven Earth years, and the most recent seasonal switch occurred in 2009 when winter gave way to spring in the northern hemisphere while summer transitioned to autumn in the southern hemisphere.

In May 2012, though, Cassini spotted something unusual. It found a huge swirling cloud several hundred miles across over Titan's south pole. This polar vortex seemed to be an effect of the change of season to autumn. What makes it especially unusual is the fact that it's located about 200 miles above the surface of the moon, where researchers believed it would be too warm for clouds to form.

So what caused the cloud in the first place? It turns out that it's made up of frozen HCN molecules. As a gas, HCN is present in small amounts in Titan's atmosphere. These frozen molecules were able to form due to the fact that the southern hemisphere of Titan had been cooling rapidly, making it possible to reach the cold temperatures needed.

"These fascinating results from a body whose seasons are measured in years rather than months provide yet another example of the longevity of the remarkable Cassini spacecraft and its instruments," said Earl Maize, Cassini project managers. "We look forward to further revelations as we approach summer solstice for the Saturn system in 2017."

The findings are published in the journal Nature.