Basic atmospheric parameters of Gl 486 b. Left: Surface temperature as a function of Bond albedo and atmospheric optical thickness, from 500 K to 2000 K in steps of 100 K. The coolest isotherms are labelled. The isotherm of 880 K, at which silicon-based surfaces melt, is drawn with a thick line. The Earth and Mars are indicated as a reference (but their T_surf do not correspond to those of Gl 486 b because of different L_* and a; see Eq. (10)). Venus, with τ ≈ 160, is out of limits. Left: Scale height as a function of surface temperature and mean molecular mass for different atmospheric compositions. From top to bottom: 90% H + 10% He (1.31 u, red), H₂ (2.02 u, orange), H₂O (18.0 u, green), N₂ (28.0 u, cyan), Earth dry air (29.0 u, blue), CO₂ (44.0 u, magenta). The dashed horizontal line indicates the Earth scale height (H_φ = 8.5 km), while the grey shaded area marks the surface temperature for rock volatilisation (T_surf ≳ 880 K).