Supersaturation on Pluto and elsewhere

The atmosphere of Pluto contains a global thin haze layer, possibly clouds and a variety of gaseous species which may be supersaturated under some conditions. Studies of Pluto climate necessitate a fairly good knowledge of the interactions between gases and aerosols since it has an impact on the vertical profiles of these species and on the fluxes of matter at the planetary scale. In this paper we use the laws of cloud nucleation to evaluate the supersaturation which is needed to trigger condensation. HCN and H2O can supersaturate by factor from several thousand to several billions depending on the type of nucleation which is used. Other species can supersaturate, but with smaller values of saturation. Gaseous species also found as ices at the surface (e.g., CO, N2, CH4) are of special interest. At a surface temperature of 37 K, they can be supersaturated with S between 1.5 to 2 even if condensation nuclei are available in large number. Such supersaturation factors have an impact on fluxes of these species from the surface to the atmosphere.