Thursday, December 20, 2012

1212.4710 (K. G. Kislyakova et al.)

XUV exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets II: Hydrogen coronae and ion escape    [PDF]

K. G. Kislyakova, H. Lammer, M. Holmström, M. Panchenko, P. Odert, N. V. Erkaev, M. Leitzinger, M. L. Khodachenko, Yu. N. Kulikov, M. Güdel, A. Hanslmeier
The interactions between the stellar wind plasma flow of a typical M star such as GJ 436 and hydrogen-rich upper atmospheres of an Earth-like planet and a "super-Earth" with the radius of 2 R_Earth and a mass of 10 M_Earth, located within the habitable zone at ~0.24 AU are studied. The formation of extended atomic hydrogen coronae under the influence of such factors as the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause) and the heating efficiency on the evolution of the hydrogen-rich upper atmospheres is investigated. XUV fluxes which are 1, 10, 50 and 100 times higher compared to that of the present Sun are considered and the formation of the high-energy neutral hydrogen clouds around the planets due to charge-exchange reaction under various stellar conditions have been modeled. Charge-exchange between stellar wind protons with the planetary hydrogen atoms and photoionization leads to the production of initially cold ions of planetary origin. Depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere we found that the ion production rates for the studied planets can vary over a wide range from ~1.0x10^{25} s^{-1} to ~5.3x10^{30} s^{-1}. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. The estimations of the long-time non-thermal escape for these planets are obtained and compared with the thermal ones. According to our estimates, non-thermal escape of ionized hydrogen atoms over a planet's lifetime varies between ~0.4 Earth ocean equivalent amounts of hydrogen (EO_H) to < 3 EO_H and usually is several times smaller in comparison to the thermal atmospheric escape.
View original: http://arxiv.org/abs/1212.4710

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