Fig. 6.

Example of the XUV volume heating production rate (top left), temperature profile (top right), density profile (bottom left) and the velocity profile (bottom right) for a hydrogen-rich martian upper atmosphere with z₀=100 km by assuming a heating efficiency of 15% (dotted lines) and 40% (dashed lines) and a temperature T₀ at the base of the thermosphere of 200 K as a function of distance in planetary radii for a hydrogen-dominated upper atmosphere at Mars, that is exposed to a 100 times higher XUV flux compared to today's solar value. The solid line shown in the velocity profiles corresponds to the escape velocity $v_{\mathrm{esc}}$ as a function of distance. The dashed–dotted lines ($\eta =15\%$) and the dashed–dotted–dotted–dotted lines ($\eta =40\%$) correspond to similar profiles but with $z_0=1000\mathrm{km}$. The hydrogen atoms reach the escape velocity below the theoretical exobase level at a location of $~35r_0$ for $\eta =15\%$ and at ~24 $r_{\mathrm{pl}}$ for $\eta =40\%$.