Origin, evolution, and fate of Titan's polar clouds.

Saturn's moon Titan exhibits a rich interplay of atmospheric chemistry and meteorology, including the seasonal formation of polar stratospheric clouds, first observed by Voyager and later by the Cassini mission. Using a global climate model with haze and cloud microphysics, we investigate their origin, evolution, and fate. We find that cloud formation begins in early autumn, triggered by rapid radiative cooling and chemical enrichment within the stratospheric polar vortex. Initially extending to 336 km altitude and composed of benzene and hydrogen cyanide ices, these clouds descend to lower altitudes during autumn and winter, evolving in composition as additional species condense, before dissipating in spring. This process reflects a unified, hemisphere-spanning seasonal mechanism shaping Titan's climate. Our model explains observed seasonal patterns and predicts the onset of the next northern polar cloud in 2027. These results provide a predictive framework for future Titan observations, missions, and long-term climate evolution studies.