Fig. 1: Modeling the annual evolution of Titan’s southern polar cloud.
a Simulated evolution of the zonally averaged total ice mass mixing ratio, over poleward latitudes higher than 60°S. Altitudes estimated from the Imaging Science Subsystem (ISS) observations are shown in brown17 and pink16, and those from the Composite Infrared Spectrometer (CIRS) observations are shown in purple22. The altitude estimated from Voyager measurements is indicated with an orange star3. The polar cloud evolves between altitudes of 75 and 336 km. Below 75 km, the region remains supersaturated in minor species throughout the year. b Simulated evolution of the zonally averaged mass mixing ratio of each ice above 75 km (color solid curves) and between 30 and 75 km (color dashed curves). Vertical lines correspond to key phases of the polar cloud evolution, depending on Titan’s season and solar longitude (LS): a March 2009 (LS = 355.7°), end of southern summer, before cloud formation; b April 2012 (LS = 32.1°), first detection of the southern polar cloud16; c June 2012 (LS = 34.5°), observation of the cloud patch near Titan’s south pole17; d July 2013 (LS = 47.7°) and e February 2015 (LS = 65.3°), detection of C6H6 ice in the southern polar cloud22; f April 2017 (LS = 89.7°), end of southern autumn, last observation of the southern polar cloud14; g May 2022 (LS = 146.5°), mid-southern winter, corresponding season of the northern polar cloud observation in December 200612; h December 2024 (LS = 175.7°), corresponding season of the northern late-winter annular opacity feature observation12; i October 2028 (LS = 224.2°), beginning of southern spring, analogous season of northern polar cloud dissipation14; j January 2030 (LS = 239.9°), disappearance of the polar cloud in the model during the second half of spring.
