Magnetospheric protection of ``Hot Jupiters'': The key role of magnetodisks in scaling

1. Magnetospheric protection of ``Hot Jupiters'': The key role of magnetodisks in scaling of a planetary magnetospheric obstacle M. L. Khodachenko 1, I. I. Alexeev 2, E. Belenkaya 2, H. Lammer 1 (1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria, (2) Institute of Nuclear Physics, Moscow State University, Moscow, Russia,

2. Exoplanet – Status Jun. 2011 usual Giants Hot Jupiters >0.2 MJ < 0.3 AU 165 (29%) • • Solar system planets • • • ? Evolution of planets ? Formation of terrestrial type worlds • 33 planets, <10 mEarth • 11 planets, < 5 mEarth • 465 Exoplanetary systems • 556 Exoplanets • 57 Multiple Planetary systems Super-Earths ?

3. Exoplanet evolution – mass loss EXOBASE ●Stellar X-ray and EUV induced expansion of the upper atmospheres Stellar XUV luminosity energy deposition to upper atmospheres

4. Exoplanet evolution – mass loss Magnetically protected planet Early Earth present Earth present Venus, Mars, or Titan Magnetically non-protected planet ●Soft X-ray and EUV induced expansion of the upper atmospheres high thermal & non-thermal loss rates The size of magneto- sphere is a crucial parameter Thermal escape: particle energy > WESC  Jeans escape–particles from “tails”  hydrodynamic escape – all particles Non-thermal escape:  Ion pick-up  Sputtering (S.W. protons & ions)  Photo-chemical energizing & escape  Electromagnetic ion acceleration

5. Exoplanet magnetic fields – role in planet protection Busse, F. H., Phys. Earth Planet. Int.,12, 350, 1976 Interval of possible values for planetary magnetic dipole: Mmax … Mmin J.-M. Grießmeier, A&A, 2004, 425, 753 J.-M. Grießmeier,Astrobiology, 2005,5 Stevenson, D.J., Rep. Prog. Phys., 46, 555, 1983  Mizutani, H., et al., Adv. Space Res., 12, 265, 1992 Mizutani, H., et al., Adv. Space Res., 12, 265, 1992 Sano, Y., J. Geomag. Geoelectr, 45, 65, 1993 ●Magnetic moment estimation from scaling laws  range for possible M rc - radius of the dynamo region (“core radius”): rc ~ MP0.75 RP-0.96 c - density in the dynamo region - conductivity in the dynamo region  - planet angular rotation velocity

6. Exoplanet magnetic fields – role in planet protection ●Magnetic moment estimation from scaling laws  range for possible M  Limitation of Mby tidal locking [Grießmeier, J.-M., et al., Astrobiology, 5(5), 587, 2005] Tidal locking strongly reduced magnetic moments HD 209458b : M = (0.005 … 0.10) MJup

7. Exoplanet magnetic fields – role in planet protection ●Non-thermal mass loss of a Hot Jupiter with a dipole type magnetosphere (a problem of protection against of strong atm. erosion) Khodachenko et al., PSS, 55, 631, 2007; Khodachenko et al., Astrobiology, 7, 167, 2007 CME induced H+ ion pick-up loss at 0.05 AU for ‘Hot Jupiters’  HD209458 b Mass loss ~1011 g/s even for weak CMEs & Mmax strong magn. protection in reality

8. Exoplanet magnetospheres – importance of magnetodisk J.-M. Grießmeier, A&A, 2004, 425, 753 Relatively large amount of observed Hot Jupiters (29%): ”survival” of close-in giants indicates their efficient protection against of extreme plasma and radiation conditions All estimations were based on too simplified model Magnetospheric protection of exoplanets was studied assuming a simple planetary dipole dominated magnetosphere  dipole mag. field B = Bdip ~ M / r3 balances stellar wind ram pressure  big M are needed for the efficient protection (but tidal locking  small M  small Rs) Specifics of close-in exoplanets  new model  strong mass lossof a planet should lead to formation of a plasma disk (similar to Jupiter and Saturn)  Magnetodisk dominated magnitosphere  more complete planetary magnetosphere model, including the whole complex of the magnetospheric electric current systems

9. Exoplanet magnetospheres – importance of magnetodisk • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’ Semi-analytical model. Key assumption: magnetopause is approximated by paraboloid of revolution along planet-star (VSW) line PMM considers mag. field of different currentsystems on the boundaries and within the boundaries of a planetary magnetopause:  planetary magnetic dipole;  current system of magnetotail;  magnetodisk;  magnetopause currents;  magnetic field of stellar wind, partially penetrated into the magnetospheric obstacle. I.Alexeev, 1978, Geomag.&Aeronomia, 18, 447. I.Alexeev et al., 2003, Space Sci. Rev., 107, 7. I.Alexeev, E.Belenkaya, 2005, Ann. Geophys., 23, 809. M.Khodachenko et al., ApJ, 2011 (submitted)

10. Exoplanet magnetospheres – importance of magnetodisk ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’ Formation of magnetodisk  “sling” model: dipole mag. field can drive plasma in co-rotation regime only inside “Alfvenic surface” (r < RA); Centrifugal inertial escape of plasma for r>RA  “material-escape driven” models:  Hydrodynamicescape of plasma (a) Fully ionized plasma outfow – Similarity with heliospheric current sheet (disk) (b)Partially ionized material outflow Background magn.field (dipole), charge separation electric field, ambipolar diffusion, azimuth.Hall current in equator.plane

11. Exoplanet magnetospheres – importance of magnetodisk RA dΘ ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’ Formation of magnetodisk – “sling” model (analogy with the Jupiter):  “Alfvénic surface” radius RA Co-rotation until = , RA:  is estimated from thermal mass loss Increase of and  decrease of RA 

12. Exoplanet magnetospheres – importance of magnetodisk scaled in Jovian parameters  Increase of ωp , dMp(th) /dt  increase of RS ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’ Magnetic field structure in PMM with magnetodisk  r < RA: magnetic field of dipole (~R-3)  r > RA: conservation of m.flux reconnected across the disc  m.field of the disk (and current density)~R-2 Determination of sub-stellar magnetopause distance: pressure balance condition   Decrease of RA increase of RS

13. Exoplanet magnetospheres – importance of magnetodisk ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’ Magnetosphere at 0.045 AU, RS = 8.0 RJ (tidally locked) Magnetosphere at 0.3 AU, RS = 24.2 RJ (tidally un-locked)

14. Exoplanet magnetospheres – importance of magnetodisk ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’  magnetospheric parameters (estimated and calculated) (Jupiter)

15. Conclusions Magnetodisks of close-in giant exoplanets (Hot Jupiters) influence the structure and character of their manetospheres, leading to a new type of „magnetodisk dominated“ magnetosphere. Extended up to (40 – 70) % magnetodisk magnetospheres, as compared the to dipole type ones, may efficiently protect planetary environments, even close to a host star.