Profiles along the planet-to-star direction. Left: temperature (black line) and velocity (grey line) of protons (in 10⁴ K and km s⁻¹, respectively; the scale for both is on the right axis) and density of major species labelled in the plot (left axis). Right: rates of the reactions responsible for the processes of population and depopulation of metastable He I listed in the legend. The black line shows the sum of reactions 1 and 2, while the blue line is the sum of reactions 7 and 8 (see legend). The x axes are in units of planetary radii.