Mean radial density profiles of the neutral (blue dots) and singly ionized (red dots) magnesium populations in the cometary tail. Profiles correspond to the best-fit simulation in the G-scenario and are plotted from the exobase level (R_exo = 3 R_p). Electron-recombination compensates for ionization in the Mg-rec layer below R_eq = 13.4 R_p (dashed black line), with a very high efficiency below R_rec = 3.9 R_p (dashed blue line). Density of ionized magnesium below ~5 R_p must be taken with caution as ionized particles are few and far between at these altitudes.