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Exoplanets

The discovery of more than 350 Jupiter-size exoplanets at very short orbital distances raises questions of atmospheric stability against thermal and non-thermal escape. Upper planetary atmospheres are mainly controlled by absorption of X-rays and extreme ultraviolet (XUV) radiation of their stars. The high radiation and strong stellar wind exposure at orbital periods less than 1 AU can lead to large exospheric temperatures and thermal escape rates, which is typical for hydrogen-dominated thermospheres. In cases where the planet is in orbits less than 0.1 AU the heating leads to hydrodynamic atmospheric conditions and planetary winds for Uranus- and Jupiter-class planets. Hydrogen-rich Uranus-class planets may even lose their entire atmospheres by this process and evolve into a new kind of terrestrial-like bodies. Afterwards, these planets might develop secondary atmospheres by out-gassing their remaining ice-rocky cores.

Recent studies indicate that, at orbital distances less than 0.03 AU, Jupiter-class exoplanets can fully evaporate over their age, which could explain the paucity of exoplanets detected at these small orbital distances. On the other hand the close orbital distance of planetary obstacles to their host stars will lead to extreme interaction-conditions for planetary obstacles in the stellar wind, or if they are hit by CME-magnetic clouds, etc. (CME = Coronal Mass Ejections). These interaction processes may lead to reconnection between planetary and stellar magnetic fields, high energetic particles beams, which can hit the stellar surface and may produce Jupiter-Io like phenomena.

Space-borne telescopes like COROT are using high precision photometry and the transit technique will have the capability to detect exoplanets with sizes of about 2 Earth radii and larger at orbital distances up to 0.5 AU. The theoretical studies carried out at IWF are important for the mission because they give information on planetary mass-relations as function of distance to the stars and may help to identify observable stellar processes, which are triggered due to planetary plasma phenomena.

The COROT mission observes up to 6000 stars in one run simultaneously. Each measured light curve needs to be filtered for stellar activity and investigated for transit-like signals.

Future development will include the search for planets in binary systems and planetary systems around solar-like stars.

Latest information on exoplanets is found at Paris Observatory.

Publications

1.  Guenther et al.: Constraints on the exosphere of CoRoT-7b, Icarus, 525, A24, 2011.
2.  Mura et al.: Comet-like tail-formation of exospheres of hot rocky exoplanets: Possible implications for CoRoT-7b, Icarus , 211, 1-9, doi:10.1016/j.icarus.2010.08.015, 2011.
3.  Ekenbäck et al.: Energetic neutral atoms around HD 209458b: Estimations of magnetospheric properties, Astrophys. J., 709, 670–679, doi:10.1088/0004-637X/709/2/67, 2010.
4.  Lammer et al.: Exoplanet status report: Observation, characterization and evolution of exoplanets and their host stars, Solar Syst. Res., 44, 290-310, doi:10.1134/S0038094610040039, 2010.
5.  Lammer et al.: Geophysical and atmospheric evolution of habitable planets, Astrobiol, 10, 45-68, doi:10.1089/ast.2009.0368, 2010.
6.  Grießmeier et al.: On the protection of extrasolar Earth-like planets around K/M stars against galactic cosmic rays, Icarus, 19, 526-535, doi:10.1016/j.icarus.2008.09.015, 2009.
7.  Lammer et al.: What makes a planet habitable?, Astron. Astrophys., 17, 181–249, doi:10.1007/s00159-009-0019-z, 2009.
8.  Holmström et al.: The origin of hydrogen around HD 209458b. Reply, Nature, 456, E1-E2, doi:10.1038/nature07403, 2008.
9.  Holmström et al.: Energetic neutral atoms as the explanation for the high-velocity hydrogen around HD 209458b, Nature, 451, 970-972, doi:10.1038/nature06600, 2008.
10.  Penz et al.: Influence of the evolving stellar X-ray luminosity distribution on exoplanetary mass loss, Astron. Astrophys., 477, 309-314, doi: 10.1051/0004-6361:20078364, 2008.
11.  Yelle et al.: Aeronomy of extra-solar giant planets, Space Sci. Rev., 139, 437-451, doi:10.1007/s11214-008-9420-6, 2008.
12.  Erkaev et al.: Roche lobe effects on the atmospheric loss from ''Hot Jupiters'', Astron. Astrophys., 472, 329-334, doi:10.1051/0004-6361:20066929, 2007.
13.  Khodachenko et al.: Mass loss of Hot Jupiters - Implications for CoRoT discoveries. Part 1: The importance of magnetospheric protection of a planet against ion loss caused by coronal mass ejections, Planet. Space Sci., 55, 631-642, 2007.
14.  Khodachenko et al.: Coronal mass ejection (CME) activity of low mass M Stars as an important factor for the habitability of terrestrial exoplanets. I. CME impact on expected magnetospheres of Earth-like exoplanets in close-in habitable zones, Astrobiol., 7, 167-184, 2007.
15.  Lammer et al.: Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones, Astrobiol., 7, 185-207, 2007.
16.  Khodachenko et al.: The importance of magnetospheric protection of “Hot Jupiters” against ion loss caused by Coronal Mass Ejections: Implications for CoRoT discoveries, Part II, submitted to Planet. Space Sci., 2006.
17.  Langmayr et al.: Hydrodynamic modelling of atmospheric evaporation of hydrogen-rich “Hot Jupiters”: Implications for CoRoT discoveries, Part I, submitted to Planet. Space Sci., 2006.
18.  Erkaev et al.: Plasma and magnetic field parameters in the vicinity of short-periodic giant exoplanets, Astrophys. J. Suppl., 157, 396-401, 2005.
19.  Grießmeier et al.: Cosmic ray impact on Earth-like planets in close-in habitable zones, Astrobiol., 5, 587-603, 2005.
20.  Jaritz et al.: Roche lobe effects on expanded upper atmospheres of short-periodic giant exoplanets, Astron. Astrophys., 439, 771-775, 2005.
21.  Baraffe et al.: The effect of evaporation on the evolution of close-in giant planets, Astron. & Astrophys., 419, L13-L16, 2004.
22.  Grießmeier et al.: The effect of tidal locking on the magnetospheric and atmospheric evolution of “Hot Jupiters'', Astron. Astrophys., 425, 753-762, 2004.
23.  Léger et al.: A new family of planets? "Ocean-Planets", Icarus, 169, 499–504, 2004.
24.  Lammer et al.: Atmospheric Loss of Exoplanets Resulting from Stellar X-Ray and Extreme-Ultraviolet Heating, Astrophys. J. Lett., 598, L121-L124, 2003.
Last update: 12/29/09
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