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The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f,Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent most likelyplanets which are surrounded by dense H/He envelopes or contain deep H2O oceansalso surrounded by dense hydrogen envelopes. Although these "super-Earths" areorbiting relatively close to their host stars, they have not lost theircaptured nebula-based hydrogen-rich or degassed volatile-rich steamprotoatmospheres. Thus it is interesting to estimate the maximum possibleamount of atmospheric hydrogen loss from a terrestrial planet orbiting withinthe habitable zone of late main sequence host stars. For studying thethermosphere structure and escape we apply a 1-D hydrodynamic upper atmospheremodel which solves the equations of mass, momentum and energy conservation fora planet with the mass and size of the Earth and for a "super-Earth" with asize of 2 R_Earth and a mass of 10 M_Earth. We calculate volume heating ratesby the stellar soft X-ray and EUV radiation and expansion of the upperatmosphere, its temperature, density and velocity structure and related thermalescape rates during planet's life time. Moreover, we investigate under whichconditions both planets enter the blow-off escape regime and may thereforeexperience loss rates which are close to the energy-limited escape. Finally wediscuss the results in the context of atmospheric evolution and implicationsfor habitability of terrestrial planets in general.

XUV exposed non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: Atmospheric expansion and thermal escape