Haze formation and distribution on Titan

Titan photochemical haze is global, optically thick and has a large vertical extension. It completely hides to observers most of the lower atmosphere and surface features. Haze is also a central component of Titan climate. It is produced from photochemistry of nitrogen and methane, which are destroyed by energetic particles and ultraviolet photons. Through its optical properties, haze strongly modifies the thermal equilibrium, and interacts with dynamics to produce a strong positive feedback. Lower haze aerosols are believed to trigger clouds formation. Finally, interaction between surface and atmosphere (and then haze) is completely unknown due to a lack of information. In this paper, our goal is modest in regard of this complexity. We describe the main properties of Titan's haze; the large-scale structures, its annual cycle, the structure of aerosol particles and, finally, the little knowledge we have about composition and photochemical sources of aerosols.