Abstract
Early during Titan’s southern fall, images captured by Cassini’s Imaging
Science Subsystem (ISS) revealed the formation of a large cloud above
Titan’s south pole. Subsequent analysis of Cassini data revealed the
cloud contained HCN ice, but the cloud’s evolution has not been
examined. We reviewed imagery of Titan’s south pole between 2012 and the
end of mission at Ls=93°. We find evidence of cloud formation as early
as Ls=32° (April 2012), one terrestrial month earlier than previously
reported, after which the cloud persists until Ls=79° (mid 2016). The
cloud top altitude descended from about 320 km at Ls=32° to below 230 km
by Ls=79°, at which point it became obscured by atmospheric methane
absorption. The cloud also grew laterally; initially confined poleward
of 81°S, by Ls=75° the cloud extended as far as 64.5°S. These
measurements place new constraints on Titan’s polar stratospheric
temperature structure and circulation during southern fall.