Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Extrasolar PlanetsGeneral Properties and Magnetospheric Aspects
Uwe Motschmann
Institute for Theoretical Physics, Technical University of Braunschweig, Germany
Co-workers:
J.M. Griessmeier, TU BraunschweigS. Preusse, MPS Katlenburg-Lindau
E. Kuehrt, DLR BerlinH. Rucker, IWF Graz
G. Mann, AIP PotsdamA. Lipatov, Moscow
Workshop Solar Terrestrial Interactions, Sinaia, September 2005
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Outline
Discovery
Properties
Detection techniques
Magnetic interaction with the host star
Planetary radio emission
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Known Extrasolar Planets (ESP)(24 August 2005)
163 planets
139 planetary systems[http://www.obspm.fr/encycl/encycl.html]
First ESP was detected in 1995[Mayor & Queloz, Nature ,1995]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Distribution of ESP
They are everywhere!
[http://capote.pharm.uky.edu/Skymap1.htm]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Definition of ESP
Spherical metal rich non-fusor
in an orbit around a fusor
outside the solar system
[Neuhäuser, http://www.astro.uni-jena.de]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Orbital Radii
[http://jilawww.colorado.edu/~pja/planets/extrasolar.html]
“Hot Jupiters”:~30 planets
with d<0.1 AU (2004)
Terrestrial planets: not (yet)
detectable
?
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection Techniques
• direct imaging• radial velocity method (Doppler shift)• transit (dimming of star)• secondary transit (dimming of planet)• astrometry• microlensing
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection by Doppler Shift(Radial Velocity Method)
Motion around center of mass → shift of spectral lines.
Detected ESP parameters: M sin(i), T, e
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection by Transit
Transit of planet in front of the star
→ decrease of total intensity (1).
Detected ESP parameters: M, T, R
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection by Secondary Transit
Second. transitPrimary transit
transit in front of star
decrease of total intensity (1)
transit behind star
decrease of IR intensity (0.25)
planetary emission
temperature of planet
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection by Astrometry
motion around center of mass → observed motion of the star.
Detected parameters: M, T
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Detection by Microlensing
Light from a distant star focussed by gravity
→ fine structure caused by planet.
Detected parameters: Mp/Ms, R, orbit
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Direct Imaging
Infrared or vis imaging (adaptive optics)
→ optical separation of planet possible.
Detected parameters: R, spectrum
[Neuhäuser et al, A&A, 2005]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Summary: Detection Methods
1?
(2005) (GP Lupi)
Direct obs.
1
2002(Gl 876 b)
Astro-metry
28>100
2003 (O235/M53)
2000(HD
209458b)
1995(51 Peg b)
Micro-lensing
TransitDoppler
shiftSecond. Transit
2004 (HD
209458b)
2
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Magnetic Interaction of ESP
• Interaction of ESP with stellar wind– Stellar wind– ESP (planetary magnetic field, …)
• Action of the stellar wind to ESP• Re-action of the ESP to star• Purpose of the study
– New phenomena compared with solar system– Observable consequences: superflares, planetary radio
emission
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Stellar Wind Models
• Parker [1958]• hydrodynamic approach• spherical symmetry• no rotation• no selfconsistent magnetic field
• Weber & Davis [1967]• magnetohydrodynamic approach• axisymmetric• rotation• magnetic field
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Parker’s Wind
0 1 2 3 4 5-3
-2
-1
0
1
2
3
0
1
2
Noz
zle
radi
us /
criti
cal r
adiu
s
distance / critical radius
Velocity / sound speed
Sonic point
Rcrit☼ = 8 ·106 km
= 0.05 AU
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Weber and Davis’ Wind
→ 3 characteristic points: Alfven point,
supermagnetosonic point,
submagnetosonicsonic point.
→ comparison with ESP position
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080
50
100
150
200
250
300
350
400
450
500
distance in AU
velo
city
in k
ms-1
Hot Jupiter orbits
T=2.0 106 K
T=0.5 106 K
Velocities much lower with respect to 1 AU
ESP may be located within Alfvén point![Preusse et al, A&A, 2005][Lipatov et al, PSS, 2005 ]
Weber and Davis’ Wind
Prot = 3dBsurf = 1…10G
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Magnetic Communication
Close-in ESP Solar System
stellar wind velocityAlfvén velocity
Planetary disturbance is carried away by stellar wind
Planetary disturbance can reach the star
*
ESP
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Superflares
• Stellar flare– catastrophic release of magnetic energy with particle
acceleration and emission of elm radiation
• Superflare– flare at solar like star with total energy release >100 x
energy of most intensive solar flares (>3000 x vis, >1000 x in X-ray)
• Superflare rate– ~101…102y [Schaefer et al, 2000]
• No solar superflare in last 2000y
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Triggering of Superflares
• Reconnection in double star system [Simon et al, 1980]
• Reconnection of the stellar magnetic field with a close-in magnetized planetary companion [Rubenstein & Schaefer, 2000]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Internal Magnetic Field of ESP
Theoretical models scaling laws for magnetic moment
[Sano, 1993]e.g.
Conditions for large magnetic moment:
high density: possible fast rotation: limited by tidal locking
large planet: possible
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Scaling Laws for Magnetic Moment
2/72/1
2/132/12/1
4/12/74/32/1
6/12/72/13/1
42/1
c
c
c
c
c
rM
rM
rM
ErM
rM
Busse 1976
Curtis and Ness 1986
Mizutani et al. 1992
Mizutani et al. 1992
Sano 1993
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Tidal Locking of Close-in ESP
Tidal force bulge on planet
Fast rotation bulge displaced relative to star
Gravitation acts on tidal bulge spin-down
After some time: rotation=revolution
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Timescale for Locked Rotation
tidally locke
d
not tidally locked
10 Gyr0.1 Gyr [Griessmeier et al, A&A, 2004]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Magnetic Moment and Tidal Locking
strongly reduced magnetic moment
Tidal locking
[Griessmeier et al, A&A, 2004]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Size of Magnetosphere
Dipole field:
Distance
magnetopause – planet:
m n v2 Bp2/2μ0
Bp M/RM3
Magnetopause size:
Pressure equilibrium at substellar point:
RM M1/3 (n v2)-1/6 d1/3
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Stellar Wind Evolution
5.2 Gyr
Strong time dependence of stellar wind
velocity and density
Influences size of the magnetosphere
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Planetary Radio Emission in the Solar System
Flux density normalized to 1 AU
[Bastian et al, APJ. 545, 2000]
Strongly magnetized planets are nonthermal radio emitters!
ionospheric cutoff
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Cyclotron Maser Instability (CMI)
vd
vk
bJv
v
fvk
v
fn
parparc
perp
parperppar
perpc
p 3
2'100
2
22 )(
1
2
222
kc
n
c
perpperpvkb
2
1
2
2
1
c
v
refraction index
argument of Besselfunction
Lorentz factor
- resonant wave particle interaction- dispersion relation for X mode [Wu & Lee, 1979]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Power input (stellar wind):
Magnetosphere:
Empirical scaling:
[Zarka et al, Astrophys. Space Sci., 277, 293, 2001]
Prad PSW
PSW (RM /d)2
RM (M, d)
Planetary Radio Emission
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Tau Bootes b as Radio Candidate
Radio Flux normalized to 1AU [Griessmeier et al, 2005]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Radio Contrast Jupiter/Sun
ΦJ / ΦQS 103 [Griessmeier et al, A&A, 2005]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Contrast ESP/Star
Vis 10-8 [Burrows et al, APJ, 2004]IR 10-4 ...10-3 [Burrows et al, APJ, 2004]Radio >1 (>>1) [Griessmeier et al, A&A, 2005]
Contrast: Poynting flux of ESP / Poynting flux of star
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Radio Flux Reaching Earth
Robin 2: sensitivity 100 mJyat 8-80 MHzready ca. 2005?
LOFAR: sensitivity 0.3-1.0 mJyat 10-240 MHzready 2006/08?
[http://www.lofar.org]
Numerical Plasma Simulation, Technical University of Braunschweig, Germany
Outlook• Missions with defined launch time
– COROT (F, Europe, Nov 2005)
– KEPLER (NASA, Oct 2006)
– [EDDINGTON (ESA, 2008+)]
– Space Interferometry Mission (NASA, 2009)
– James Webb Space Telescope (ESA, NASA, 2009+)
– GAIA (ESA, 2008-2012)
• Planned missions– Big Occulting Steerable Satellite
– UMBRAS
– DARWIN (ESA)
– Galactic Exoplanet Survey Telescope
– Planet Imager (NASA)
– Terrestrial Planet Finder (NASA)