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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,

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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,


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 ?


EXOBASE

●Stellar X-ray and EUV induced expansion of the upper atmospheres

Stellar XUV luminosity energy deposition to upper atmospheres


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


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


●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


●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


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


●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)


●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


RA

●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


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


●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)


●Paraboloid Magnetospheirc Model (PMM) for ‘Hot Jupiters’

 magnetospheric parameters (estimated and calculated)

(Jupiter)


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.


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