Total flux (or phase function) and degree of polarization of incident unpolarized starlight that is reflected by the model planets in the 4 evolutionary phases as functions of α and λ. Left column: the total flux (or phase function). Right column: degree of polarization. First row: phase 1 (‘Current Earth’). Second row: phase 2 (‘Thin cloud Venus’). Third row: phase 3 (‘Thick cloud Venus’). Fourth row: phase 4 (‘Current Venus’). The phase functions are normalized such that at α = 0°, and they equal the planet’s geometric albedo A_G.