SP6 – MAGNETOSPHERES Magnetospheric electrodynamics of exoplanets Annual results, 2012

1. SP6 – MAGNETOSPHERESMagnetospheric electrodynamics of exoplanetsAnnual results, 2012 Maxim Khodachenko, Zoltán Vörös, Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria and Cooperating partners SINP MSU, Moscow; ILP RAS, Novosibirsk, Russia, FMI Finland

2. Major research directions & results in 2012 ●Work in progress (in line with the proposed plan) Major goal:better understanding of the physics behind the formation of and exoplanetary magnetodisk; Confirmation of the magnetodisk phenomenon ●Basic directions of work in 2012: 1. Parametric study of magnetodisk influence of the size of exoplanetary magnetosphere; Continuation of work -- implications for HD209458b 2. Analytical treatment of the case of an expanding partially ionized plasma flow in a dipole-type magnetic field; 3. Numerical MHD modelling of fully ionized plasma expansion in the presence of the background magnetic dipole field; 4. Experimental simulation of magnetodisk formation during the plasma outflow from the region occupied by the magnetic dipole field 5. Study of external triggering of magnetic reconnection in current sheets

3. Exoplanet magnetospheres – role of magnetodisk J.-M. Grießmeier, A&A, 2004, 425, 753 Relatively large amount of observed Hot Jupiters (28%): ”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 magnetosphere  more complete planetary magnetosphere model, including the whole complex of the magnetospheric electric current systems

4. Exoplanet magnetospheres – role of magnetodisk Rs Rt ●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’  Schematic view of PMM elements: Paraboloid shape: general view: x (Rt/Rs)2 = Rt2 – y2 – z2 particular case:(Rt/Rs)2 = 2 Approx. Equilibr. Shape 2x Rs = 2 Rs2 – y2 – z2 I.Alexeev, 1978, Geomag.&Aeron., 18, 447. I.Alexeev et al., 2003, Space Sci. Rev., 107, 7. I.Alexeev, E.Belenkaya, 2005, Ann. Geophys., 23, 809.

5. Exoplanet magnetospheres – role of magnetodisk scaled in Jovian parameters  Increase of ωp (i.e. decrease RA) , 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: Khodachenko et al. ApJ, 2012, 744, 70

6. 1. Paramertic study of magnetodisk influence Implications for HD209458b • - Orbital parameters d  0.045 AU around a solar-like G star - Mass of planet Mpl  0.69 MJup - Planet radius Rpl  1.35 RJup - Estimated magnetic momentsμ = (0.03 – 0.1) μJup – tidal lock model • μ= 0.41 μJup– evolution model - Estimated mass loss rates1011 g/s (inner bound. temp. 11000K) 3 x 1010 g/s (inner bound. temp. 8000K) 3 x 109 g/s (inner bound. temp. 6000K) - Stellar wind parameters nsw= 9.1 x 103 cm-3  Vsw= 210, 330, 450 km/s

7. 1. Paramertic study of magnetodisk influence Implications for HD209458b  μp = 0.1 μJ

8. 2.Expanding partially ionized plasma flow in a dipole-type magnetic field: Analytic treatment ●Partially ionized plasma case: •  m.Field (planetary intrinsic m.dipole) is not frozen into plasma •  neutral gas slips through m.Field and plasma → charge separation • Electr.field Ecs, ambipolar diffusion •  Strong anisotropy of conductivity • Strong magnetic tension forces acting on the expanding plasma ●Similarity with intense m.tube formation in solar photosph.conv.flow: - Hall current JH ~ [B x ECS] distorts the background m.field

9. 2.Expanding partially ionized plasma flow in a dipole-type magnetic field: Analytic treatment - velocity of the center of mass - pressure function - conductivity and - relative densities - momentum due to collisions with neutrals ●Partially ionized plasma case: Generalized Ohm‘s law: where usually << 1

10. 2.Expanding partially ionized plasma flow in a dipole-type magnetic field: Analytic treatment  projection of the Generalized Ohm‘s Law on φ-axis normalized variables ; ; plasma characteristic parameters ; ; magnetic Reynolds number in partially ionized plasma ●Partially ionized plasma case:  look for a m.field configuration (Br, Bθ, Bφ=0), co-existing with (Vr, Vθ=0, Vφ=0)  assume axial symmetry, i.e. d/dφ =0 ; p(r) where

11. 2.Expanding partially ionized plasma flow in a dipole-type magnetic field: Analytic treatment   assume incompr.flow, i.e. solutions: 1) = Const 2) ●Partially ionized plasma case:  look for a solution in the form rAφ= Φ(r,θ) = Φ(r) Sin θ  asymptotic case r→∞( >> R0) : , → 0 , → = 

12. 3.MHD simulation of plasma expansion in the background magnetic dipole field ●Fully ionized plasma case: numerical simulation with MHD (Inst.of Laser Phys. Russ.Acad. of Sciences) - pressure P0 and density ρ0 in the inner boundary - initial dipole magnetic field plasma is key parameter Plasma preassure maps for different β Column density & mass loss rate as function of β „Dead zone“ size as function of β - formation of a „dead zone“ (r < RA) where plasma is „locked“ by dipole field - beyond RA the region of open filed lines and magnetodisk

13. 3.MHD simulation of plasma expansion in the background magnetic dipole field ●Fully ionized plasma case: -outside “dead zone” (r > RA) magnetic field is progressively compressed near the equatorial plane by plasma flow  formation of thin current sheet (disk) -flux accumulation  reconnection which removes the added flux. -For reconnection is stationary  acceleration of plasma outside of the dead point. Jφdistribution for β=10-2 Equatorial (Z=0) profile of velocity and current for β=10-2

14. 4.Experimental simulation of magnetodisk formation ●Laboratory plasma experiment: Vacuum chamber KI-1 at Institute of Laser Phys., Russ. Acad. Sci. Novosibirsk - vacuum chambers (120x500 cm; 100x55 cm) - dipole magnetic field (5x5 cm, Md = 3 x 105 G cm3); discharge plasma injectors - diagnostics with 1) Langmuire probe (charge dens.); 2) Faraday cap (ion flux); 3) Rogovskii coil (electric current). All sensors are movable. - sequence of pulses (V = 50, 40, 30 km/s, n = 1012 - 1013 cm-3), C+ & 2 H+

15. 5.Study of the external triggering of magnetic reconnection in thin current sheets -60RE GUMICS-4 code, Finnish Meteorological Institute X-Y plane THB THC ION DENSITY 7o Directional changes and pressure pulses in the solar wind compress and shift the magnetotail to a new position. Compressions lead to thin current sheet configurations and magnetic reconnection.

16. 5.Study of the external triggering of magnetic reconnection in thin current sheets Global MHD simulation and observation of reconnection signatures in the tail; (Vörös et al. in prep.) Thinning current sheet favourable for magnetic reconnection Bx Statistics: ~2/day long duration directional changes in the SW between 1995-2012; Close-in exoplanets: reconnection regime and triggering can be controlled by both internal (e.g. plasma beta – see simulation results, point 3.above) and external factors, such as stellar wind flow directional changes and pressure pulses. Bz P1 Plasmoids observed by P1 in the tail Bx Pressure puls Bz electron density reconnection site Plasmoid flux of accelerated electrons

17. Future work & internal cooperation plans ●Continuation of the work ♦ MHD and Hybrid simulations (fully ionized case): inclusion of the effects of planet gravity; rotation and more realistic energy deposition model in the upper atmosphere/ionosphere; ♦MHD (partially ionized case): The anatomy of "inner roots" of magnetodisk will be studied numerically (based on the obtained analytical solutions); ♦Development of kinetic plasma approaches for description of structure of the thin current sheet of the equatorial magnetodisk; ♦Simulation (MHD and Hybrid) of interaction of magnetodisk-dominated magnetospheres with the stellar winds; ♦ Investigation of the external triggering of magnetic reconnection for the case of close-in exoplanets; ♦Organization of continuation of laboratory experiments: Search for addi- tional funding; communication with the European Task Force in Laboratory Astrophysics (ETFLA) of the ASTRONET project

18. Future work & internal cooperation plans ●Collaboration with other sub-projects ♦ With SP07 (ongoing): characterization of possible exoplanetary magneto- spheric obstacles. ♦With SP03 (the newly discovered): modelling of plasma expansion in the presence of a dipole-type (rotating) magnetic field. Similarity between stellar winds and exopanetary material escape. ♦With SP02 (in future): exoplanetary magnetodisk MHD/HYB model may be of interest for the extension of the present hydrodynamic model of a stellar disk to include the electromagnetic fields. ♦With SP08 (in future): planetarymagnetospheres in binary systems.