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arXiv · 1312.4721

Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"

K. G. Kislyakova·C. P. Johnstone·P. Odert·N. V. Erkaev·H. Lammer·T. Lüftinger·M. Holmström·M. L. Khodachenko·M. Güdel
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Abstract

We study the interactions between stellar wind and the extended hydrogen-dominated upper atmospheres of planets and the resulting escape of planetary pick-up ions from the 5 "super-Earths" in the compact Kepler-11 system and compare the escape rates with the efficiency of the thermal escape of neutral hydrogen atoms. Assuming the stellar wind of Kepler-11 is similar to the solar wind, we use a polytropic 1D hydrodynamic wind model to estimate the wind properties at the planetary orbits. We apply a Direct Simulation Monte Carlo Model to model the hydrogen coronae and the stellar wind plasma interaction around Kepler-11b-f within a realistic expected heating efficiency range of 15-40%. The same model is used to estimate the ion pick-up escape from the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b-f. From the interaction model we study the influence of possible magnetic moments, calculate the charge exchange and photoionization production rates of planetary ions and estimate the loss rates of pick-up H+ ions for all five planets. We compare the results between the five "super-Earths" and in a more general sense also with the thermal escape rates of the neutral planetary hydrogen atoms. Our results show that for all Kepler-11b-f exoplanets, a huge neutral hydrogen corona is formed around the planet. The non-symmetric form of the corona changes from planet to planet and is defined mostly by radiation pressure and gravitational effects. Non-thermal escape rates of pick-up ionized hydrogen atoms for Kepler-11 "super-Earths" vary between approximately 6.4e30 1/s and 4.1e31 1/s depending on the planet's orbital location and assumed heating efficiency. These values correspond to non-thermal mass loss rates of approximately 1.07e7 g/s and 6.8e7 g/s respectively, which is a few percent of the thermal escape rates.

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K. G. Kislyakova, C. P. Johnstone, P. Odert, N. V. Erkaev, H. Lammer, T. Lüftinger, M. Holmström, M. L. Khodachenko, M. Güdel. 2014-01-22. Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths". https://doi.org/10.1051/0004-6361%2F201322933

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