  The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f,
Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent most likely
planets which are surrounded by dense H/He envelopes or contain deep H2O oceans
also surrounded by dense hydrogen envelopes. Although these "super-Earths" are
orbiting relatively close to their host stars, they have not lost their
captured nebula-based hydrogen-rich or degassed volatile-rich steam
protoatmospheres. Thus it is interesting to estimate the maximum possible
amount of atmospheric hydrogen loss from a terrestrial planet orbiting within
the habitable zone of late main sequence host stars. For studying the
thermosphere structure and escape we apply a 1-D hydrodynamic upper atmosphere
model which solves the equations of mass, momentum and energy conservation for
a planet with the mass and size of the Earth and for a "super-Earth" with a
size of 2 R_Earth and a mass of 10 M_Earth. We calculate volume heating rates
by the stellar soft X-ray and EUV radiation and expansion of the upper
atmosphere, its temperature, density and velocity structure and related thermal
escape rates during planet's life time. Moreover, we investigate under which
conditions both planets enter the blow-off escape regime and may therefore
experience loss rates which are close to the energy-limited escape. Finally we
discuss the results in the context of atmospheric evolution and implications
for habitability of terrestrial planets in general.
