IWF Graz … 1 H. Lammer (1), M. L. Khodachenko (1), H. I. M. Lichtenegger (1), Yu. N. Kulikov (2), N. V. Erkaev (3), G. Wuchterl (4), P. Odert (5), M. Leitzinger (5), J. Weingrill (1), A. Hanslmeier (5), T. Penz (6) (1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria (2) Polar Geophysical Institute, Russian Academy of Sciences, Murmansk, Russian Federation (3) Institute for Computational Modelling, Russian Academy of Sciences, and Siberian Federal University, Russian Federation (4) Thüringer Landessternwarte Tautenburg, Tautenburg, Germany (5) Institute for Physics, University of Graz, Graz, Austria (6) On leave from the INAF - Osservatorio Astronomico, Palermo, Italy Determining the mass loss boundary for hot gas giants: What can we learn from transit observations? 1 th CoRoT Symposium, February , Paris, France, 2009

IWF Graz … Motivation  What is the effect on the mass evolution of close-in gas giants related to thermal and non-thermal atmospheric escape?  Are these loss processes efficient enough to remove the hydrogen inventory of very close gas giants during their life-time?  What is the influence of these loss processes to the mass and size of discovered hot Neptune`s and other lower mass exoplanets? Energy limited approaches → thermal escape modelling - Lammer et al. [ApJ 598, L121, 2003] → evolution studies (Loss overestimation) - Baraffe et al. [A&A 419, L13, 2004] → evolution studies (Loss overestimation) - Lecavalier des Etangs et al. [A&A 418, L1, 2004] (Loss overestimation) - Lecavalier des Etangs [A&A 461, 1185, 2007] → evolution studies (Loss overestimation) - Hubbard et al. [Icarus 187, 358, 2007] - Hubbard et al. [ApJ 685, L59, 2007] - Penz et al. [A&A 477, 309, 2008] → evolution studies Hydrodynamic approaches → thermal escape modelling - Yelle [Icarus 170, 167, 2004] - Tian et al. [ApJ 621, 1049, 2005] - Gracia Muñoz [PSS 55, 1426, 2007] - Penz et al. [PSS 56, 1260, 2008] → evolution studies Stellar plasma – atmosphere erosion → non-thermal escape modelling - Erkaev et al. [ApJS 157, 396, 2005] - Khodachenko et al. [PSS 55, 631, 2007] → evolution studies 2

IWF Graz … 3 Thermal escape of hydrogen from close-in gas giants → non-linear process Penz et al. [PSS, 56, 1260, 2008] Penz et al. [A&A 477, 309, 2008] HD209458b at AU Hydrodynamic approach Energy limited approach incl. Roche lobe effect G stars → XUV evolution Solar proxies - Sun in Time program -

IWF Graz … Loss enhancement due to the Roche Lobe 4 η K is the potential energy reduction factor due to the stellar tidal forces Penz et al. [PSS, 56, 1260, 2008] Erkeav et al. [A&A 472, 329–334 (2007)] HD209458b at 0.02 AU

IWF Graz … 5 Thermal escape of hydrogen from close-in gas giants Based on the hydro-loss model of Penz et al. [A.&A, 477, 309, 2008]; Penz et al. [PSS, 56, 1260, 2008] EGP I: M EGP I = 1 × g  16.7 M Earth ~ 1 M Neptune EGP II: M EGP II = 1 × g  167 M Earth ~ 1.75 M Saturn ~ 0.5 M Jupiter A Neptune-type body can loose its hydrogen envelope due to thermal escape Thermal escape is not efficient enough to evaporate a Hot Jupiter down to its core size

IWF Graz … 6 ● Parameters of CMEs: density ♦ At the larger distances (0.3 – 1) AU n CME and  CME are measured in-situ by spacecraft. Magnetic Clouds (MCs) – the indicator of far CME ♦ White-light SoHO/LASCO coronagraphs images  empirical power-law dependence for n CME (d) ( Lara, et al., Geofísica Internacional, 43, 75, 2004 ): n CME (d) = n 0 (d / d 0 )  - good approximation within  20 R Sun ( n 0 ~ (5-50)x10 5 cm -3 ; d 0 ~ (3 - 5)R Sun ) n MC (d) = n 0 MC (d / d 0 )  - approximation at > 0.3 AU ( n 0 MC = 6.47  0.95 cm -3 ; d 0 = 1 AU ) n min CME (d) = 4.88 (d / d 0 ) -2.3 n max CME (d) = 7.10 (d / d 0 ) -3.0 with d 0 = 1 AU Stellar wind & CME activity → extreme plasma interaction → non-thermal escape [Khodachenko et al. PSS, 55, 631, 2007]

IWF Graz … Stellar plasma propagation modelling 7 For G-type stars using the Sun as a proxy

IWF Graz … 8 Estimation of stellar plasma induced ion erosion from a Jupiter-mass exoplanet Lammer et al., in preparation based on test-particle model explained in Khodachenko et al. [PSS, 55, 631, 2007] In case the planet has no or a very weak intrinsic magnetic field the stellar plasma dynamic pressure will be ballanced by the ionospheric pressure THE QUESTION IS: at which altitude distance can the obstacle form? If the planetary obstacle builds up at a distance of about 1.5 planetary radii above the visual radius of the exoplanet, huge ion erosion can be expected!

IWF Graz … 9 Ionosphere profiles of hot Jupiter`s 0.1 AU 0.01 AU 0.45 AU 0.3 R p /R = 3.3 R p Yelle [Icarus, 170, 167, 2004]

IWF Graz … 10 Ionopause estimation for non- or weakly magnetized hot Jupiter’s R ip ≥ 3 R pl → We do not expect that stellar plasma erosion at close orbital distances is efficient enough to remove the whole hydrogen atmoshere of a hot Jupiter so that the core of these gas giants remain Closer d → higher ionoization → higher ion pressure Closer d → denser stellar plasma → lower plasma velocity Non-magnetic hot Jupiter`s: Can they survive? 3R pl

IWF Graz … Conclusions 11 Roche lobe effect becomes relevant at d ≤ 0.02 AU! All discovered hot Neptune`s are not remaining remnants of more massive gas giants! They may have lost or loose their hydrogen envelopes but they originated as lower mass planets