H. Lammer, N. V. Erkaev, P. Odert, K. G. Kislyakova, M. Leitzinger, M. L. Khodachenko
The discovery of transiting "super-Earths" with inflated radii and known masses such as Kepler-11b-f, GJ 1214b and 55 Cnc e, indicates that these exoplanets did not lose their nebula-captured, degassed or impact-delivered hydrogen-rich protoatmospheres by atmospheric escape processes. Because hydrodynamic blow-off of atmospheric hydrogen atoms is the most efficient atmospheric escape process we apply a time-dependent numerical algorithm which is able to solve the system of 1-D fluid equations for mass, momentum, and energy conservation to investigate the criteria under which hydrogen-rich "super-Earths" can experience hydrodynamic expansion by heating of the stellar XUV (soft X-rays and extreme ultraviolet) radiation and thermal escape via blow-off. Depending on orbit location, XUV flux, heating efficiency and the planet's mean density our results indicate that the upper atmospheres of all "super-Earths" can expand to large distances, so that besides of Kepler-11c all of them experience atmospheric mass-loss due to Roche lobe overflow. The atmospheric mass-loss of the studied "super-Earths" is one to two orders of magnitude lower compared to that of "hot Jupiters" such as HD 209458b, so that one can expect that these exoplanets cannot lose their hydrogen-envelopes during their remaining lifetimes.
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http://arxiv.org/abs/1210.0793
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