Total hydrogen ion production rates (charge exchange, XUV ionization, electron impact ionization) of the evaporating hydrogen atmosphere of HD 209458b at an orbital distance of 0.045 AU (slow shock regime: three upper curves) and a hypothetical similar exoplanet at 0.2 AU (fast shock regime: three lower curves) as a function of planetary radii. The solid curves correspond to an exobase H number density of 10⁴ cm⁻³, the dashed curves to ﹩5\times 10^{4}﹩ cm⁻³, and the dotted lines to 10⁵ cm⁻³.