Four evolutionary phases of the model planets (Bullock & Grinspoon 2001). In Phases 1 and 2, the clouds consist of liquid water droplets, and in Phases 3 and 4, they consist of liquid sulfuric acid solution droplets. The cloud optical thickness is indicated by b^c and the cloud particle effective radius by r_eff. For the effective variance υ_eff of the size distributions in Phases 1–3, we used 0.1, and for Phase 4 we used υ_eff = 0.07.