Three upper panels a–c present the profiles of the number density of ions (colored lines) and electrons (black line) as a function of height in the upper atmosphere of the Earth (panel a), π Men c (panel b) and Trappist-1 b (panel c). Panel d shows the electron number density of the three models on the same plot. Panel e shows the conductivity profile above 1µbar for the Earth (black lines), Trappist-1 b (blue lines) and π Men c (orange lines). The parallel conductivity σ₀ (Eq. (15)) is shown by dotted lines. We assume a constant magnetic field B_P = 0.2 G to compute the Pedersen (solid lines, Eq. (17)) and Hall (dashed lines, Eq. (16)) conductivities. The underlying atmospheric and ionospheric models are taken from IRI-2016 and NRLMSIS-00 models for the day-side Earth (see text), and García Muñoz (2023) for Trappist-1 b and π Men c.