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- Title
Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths".
- Authors
Kislyakova, K. G.; Johnstone, C. P.; Odert, P.; Erkaev, N. V.; Lammer, H.; Lüftinger, T.; Holmström, M.; Khodachenko, M. L.; Güdel, M.
- Abstract
Aims. We study the interactions between stellar winds and the extended hydrogen-dominated upper atmospheres of planets. We estimate the resulting escape of planetary pick-up ions from the five "super-Earths" in the compact Kepler-11 system and compare the escape rates with the efficiency of the thermal escape of neutral hydrogen atoms. Methods. 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 the thermal escape rates of the neutral planetary hydrogen atoms. Results. Our results show that a huge neutral hydrogen corona is formed around the planet for all Kepler-11b-f exoplanets. The nonsymmetric form of the corona changes from planet to planet and is defined mostly by radiation pressure and gravitational effects. Nonthermal escape rates of pick-up ionized hydrogen atoms for Kepler-11 "super-Earths" vary between ~6.4×1030 s-1 and ~4.1×1031 s-1, depending on the planet's orbital location and assumed heating efficiency. These values correspond to non-thermal mass loss rates of ~1.07 × 107 g s-1 and ~6.8 × 107 g s-1 respectively, which is a few percent of the thermal escape rates.
- Subjects
STELLAR winds; PLANETARY atmospheres; UPPER atmosphere; SUPER-Earths; HYDROGEN atom; KEPLER (Spacecraft)
- Publication
Astronomy & Astrophysics / Astronomie et Astrophysique, 2014, Vol 562, p1
- ISSN
0004-6361
- Publication type
Article
- DOI
10.1051/0004-6361/201322933