Notes. M_core and R_core are the mass and radius of the core, with a composition assumed to be Fe/Mg = 0.75 and Mg/Si = 1.02. R_transit are the transit radii measured by Spitzer. Adopted masses and radii are expressed in Earth units (M_⊕ and R_⊕, respectively). Surface pressures P_surf (i.e. the pressure at the core or atmosphere boundary) and transit pressures P_transit (i.e. the atmospheric pressure at the transit radius) are expressed in bars. CH₄ and H₂ O volume mixing ratios were arbitrarily fixed according to C/O solar abundances; that is, 5 × 10⁻⁴ and 1 × 10⁻³, respectively.“cond.” indicates those cases where water vapour (at solar abundance) starts to condense in the atmosphere, and should thus be highly depleted. We note that, given the assumptions made on the core composition, TRAPPIST-1e cannot accommodate a H₂ -dominated atmosphere at all.