Titan is the most interesting body in the solar system from a weather standpoint. It has a thick and robust atmosphere, a liquid cycle of methane and other hydrocarbons, and it has seasonal variations in these patterns. It’s essentially a cold and oxygen-deficient version of Earth. Because the seasons on Titan take 7.5 years to pass, we have few opportunities to study them up close with the Cassini spacecraft. So as long as Cassini is operating, we are using our time wisely to see how Titan is changing. The first major change is a giant ice cloud that has formed in the south polar region of Titan’s Stratosphere.
Seen in 2012, 300 Km above the surface, this giant ice cloud, similar to fog here on Earth, had condensed in the stratosphere. New data shows the cloud is much larger, extending deeper toward the surface down to an altitude of 200 Km. Cassini’s Infrared Spectrometer, CIRS, allowed the Cassini team to get a deeper view of the monster cloud.
“When we looked at the infrared data, this ice cloud stood out like nothing we’ve ever seen before,” said Carrie Anderson of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It practically smacked us in the face.”
Rain clouds on Earth condense when evaporated water rises with the air. The moist air reaches colder temperatures and lower pressures, condensing into a familiar cloud. On Titan the process is a little different. Gases in the warmer pole of the planet are circulated to the cooler pole, where they begin to sink due to the cooler temperatures. As they reach colder temperatures, different gases in the air mass condense to form the different layers of the ice cloud.
As Winter begins at the south pole of Titan, new clouds are forming, while the North pole clouds evaporate in the transition to Summer. “Titan’s seasonal changes continue to excite and surprise,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “Cassini, with its very capable suite of instruments, will continue to periodically study how changes occur on Titan until its Solstice mission ends in 2017.”
By studying the cloud, scientists can model the seasonal changes in an attempt to better understand the cycles in Titan’s atmosphere. By looking at the south polar cloud, they determined that the temperatures at the south pole must get down to at least -150 degrees Celsius. They also found that the seasonal changes are much more prominent moving into southern Winter than they are in the Northern hemisphere moving into Summer. “The opportunity to see the early stages of winter on Titan is very exciting,” said Robert Samuelson, a Goddard researcher working with Anderson. “Everything we are finding at the south pole tells us that the onset of southern winter is much more severe than the late stages of Titan’s northern winter.”
As Cassini continues to study the Titanic weather (pun intended), we will be able to study and model the climate of Titan, to try and understand the variety and complexity of the behavior of Titan’s atmosphere.