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M. L. Khodachenko 1, I. I. Alexeev 2, H. Lammer 1, E. Belenkaya 2, J.-M. Grieïmeier 3
(1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria, (2) Institute of Nuclear Physics, Moscow State University, Moscow, Russia, (3) LPC2E Orleans France


Exoplanet - Status Jan. 2011

usual Giants Hot Jupiters
(0.5-1,75)MJ 136 (27%)

Ç ÇÇ Ç Ç
Solar system planets

? Evolution of planets ? Formation of terrestrial
435 Exoplanetary systems 519 Exoplanets 54 Multiple Planetary systems type worlds Ç 28 planets, <10 mEarth Ç 9 planets, < 5 mEarth

Super-Earths ?


Exoplanet evolution - mass loss



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

energy deposition to upper atmospheres

EXOBASE


Exoplanet evolution - mass loss



Soft X-ray and EUV induced expansion of the upper atmospheres



high thermal & non-thermal loss rates

Thermal escape: particle energy > WESC

Jeans escape - particles from "tails" hydrodynamic escape - all particles Magnetically protected planet

The size of magnetosphere is a crucial parameter
Ion pick-up Sputtering (S.W. protons & ions) Photo-chemical energizing & escape Electromagnetic ion acceleration

Non-thermal escape:



Early Earth

present Earth present Venus, Mars, or Titan

Magnetically non-protected planet


Exoplanet magnetic fields - role in planet protection



Magnetic moment estimation from scaling laws

range for possible

M

Busse, F. H., Phys. Earth Planet. Int., 12, 350, 1976 Stevenson, D.J., Rep. Prog. Phys., 46, 555, 1983 Mizutani, H., et al., Adv. Space Res., 12, 265, 1992 planetary magnetic dipole: Mizutani, H., et al., Adv. Space Res., 12, 265, 1992 Sano, Y., J.-M. Grieïmeier,Astrobiology, 65, 5,5 J. Geomag. Geoelectr, 45, 200 1993
0.75 P -0.96 P J.-M. Grieïmeier, A&A, 2004, 425, 753



Interval of possible values for

Mmax ... Mmin

rc - radius of the dynamo region ("core radius"): rc ~ M c - density in the dynamo region - conductivity in the dynamo region - planet angular rotation velocity

R


Exoplanet magnetic fields - role in planet protection



Magnetic moment estimation from scaling laws
Limitation of

range for possible

M
]

M

by tidal locking [

Grieïmeier, J.-M., et al., Astrobiology, 5(5), 587, 2005

HD 209458b M = (0.005 ... 0 magnetic moments Tidal locking : strongly reduced .10) MJup


Exoplanet magnetic fields - role in planet protection



Magnetospheric protection of evaporating/eroded planetary atmospheres
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


Exoplanet magnetospheres - importance of magnetodisk
Relatively large amount of observed Hot Jupiters (27%):

"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)
J.-M. Grieïmeier, A&A, 2004, 425, 753

Specifics of close-in exoplanets

new model

strong mass loss of 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


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 current systems 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, Geomag.&Aeronomia, 1978, 18, 447 M.Khodachenko et al., ApJ, 2010 (submitted)

Ç ÇÇ Ç ÇÇ Ç ÇÇ Ç ÇÇ Ç ÇÇ ÇÇ Ç ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ ÇÇ Ç


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 escape of plasma "material-escape driven" models: Hydrodynamic escape 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


Exoplanet magnetospheres - importance of magnetodisk



Paraboloid Magnetospheirc Model (PMM) for `Hot Jupiters'
Formation of magnetodisk - "sling" model (analogy with the Jupiter):

"Alfvùnic surface" radius R Co-rotation until

A

=

,




RA :

R

A

d

is estimated from thermal mass loss


Increase of and decrease of R

A


Exoplanet magnetospheres - importance of magnetodisk



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 R
A



increase of R

S


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)


Exoplanet magnetospheres - importance of magnetodisk



Paraboloid Magnetospheirc Model (PMM) for `Hot Jupiters'
magnetospheric parameters (estimated and calculated)

(Jupiter)


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.