Monitoring seasonal changes on Titan
Since 2004, the international Cassini mission has been studying Saturn and its moons, including Titan. In addition to the in-situ measurements of Titan's atmosphere and surface that were made by ESA's Huygens probe in January 2005, many targetted flybys with the Cassini orbiter have provided opportunities for dedicated studies of the atmosphere and surface of the largest of Saturn's moons.
Using the Composite Infrared Spectrometer (CIRS) on the orbiter, Sandrine Vinatier and colleagues monitored the seasonal evolution of the temperature, gas and aerosol distributions in the atmosphere of Titan from 2006 to 2013.
Titan experiences seasons as it makes its 29-year orbit around the Sun along with Saturn. Each of the four seasons lasts about seven Earth years so seasonal changes are expected to be very slow. The most recent seasonal switch occurred in 2009, when summer transitioned to autumn in the southern hemisphere.
By mapping how the temperature, gas and aerosol distributions changed with the seasons the scientists could trace changes in the global circulation of the atmosphere. Their study showed that between 2007 and 2011 there was a complete reversal in the circulation of the moon's atmosphere traced out by changes in the temperature at different layers of the atmosphere and by the abundance of hydrogen cyanide (HCN) at different layers.
The seasonal changes described in this animation are based on a study reported in Seasonal variations in Titan's middle atmosphere during the northern spring derived from Cassini/CIRS observations, by Sandrine Vinatier and colleagues, published in Icarus, Volume 250, April 2015, Pages 95–115; doi: 10.1016/j.icarus.2014.11.019.