Sudden cooling of a polar hot-spot on Saturn's largest moon, Titan, may have been due to increases of trace gases in the atmosphere, reports a study in Nature Communications this week. The mechanism for this previously unexplained event is elucidated using observations from the Cassini mission.

The formation of polar hot-spots is a seasonal occurrence after the spring equinox in Titan’s higher atmosphere. However, in 2012 the sudden cooling of a hot-spot in the south pole resulted in the formation of a strong winter polar vortex, an event not predicted by models.

Nicholas Teanby and colleagues use observations retrieved by Cassini over the past 13 years to explore the formation and evolution of the south-polar vortex in Titan’s atmosphere. They find that trace gases - which have a strong cooling effect - were produced in the hot-spot, accumulation of which resulted in a change from hot conditions in 2011 to a cold spot that lasted from 2012 to 2015.

The production of these cooling trace gases high in the atmosphere, and subsequent polar vortex formation, is unique to Titan. However, the last observations made by Cassini between 2016 and 2017, before it entered Saturn’s atmosphere, suggest a return of the hot-spot maybe occurring.