Moon-Planet and Exoplanet-Star Couplings: Common Electrodynamic Interaction

Mechanisms Throughout the Universe

Joachim Saur, Timo Grambusch, Stefan Duling

University of Cologne, Germany

Magnetic coupling: Satellite-planet

Clarke et al., 2002

Magnetic coupling: Planet-star

Radial distribution of Exoplanets Evidence for Planet-Star Coupling: HD 179949

Skolnik et al. (2003, 2005, 2008)Ca 3947 A line correlation with orbital period of 3.1 dEnergy flux: 1020 W

Our aim:

• Electromagnetic planet-star interaction for exoplanets has been studied by: – Ip et al. (2004), – Preusse et al. (2005, 2006)– Grießmeier et al. (2004, 2007)– Zarka (2007)– Lanza (2008, 2009)– Nichols (2011)– Poppenhaeger et a. (2010, 2011)

• This work: Energetics of the coupling, which is dominated by the Poynting flux.

Model for energy flux• Calculate Poynting flux S= (E x B)/μ0 • Based on Alfven wing model by Neubauer (1980).

Kivelson et al. 2004 Neubauer 1998

With internal field Exoplanet geometryStandard case

Total Poynting flux launched at satellite/planet

Limitation: No considerations about the fate of the energy along the flux tube No partially reflection/transmission (Hess et al. 2010a,2010b) considered.

No nonlinear reflection at central body (Jacobsen et al. 2007) considered.No conversion of Poynting flux into particle acceleration considered.

Benchmarking at Jupiter and Saturn

• Io: – Theory: 2 x 1012 W– UV Observations: 1-10 x 1010

W • Europa:

– Theory: 1-7 x 1010 W– UV Observations: 1-5 x 108 W

• Ganymede: – Theory: 1-3 x 1011 W– UV Observations: 2-15 x 108 W

• Callisto:– Theory: 0.3-6 x 109 W

• Enceladus:– Theory: 2x108 W– UV Observations: 106-107 W

Estimated MA at all known 562* exoplanets * until last Friday

Poynting flux for 192 exoplanets with MA<1

Summary

• Electromagnetic planet star coupling is possible if relative flow velocity < Alfven velocity. 192 of 562 exoplanets exhibit sub-Alfvenic interaction.

• Only a few exoplanets generate energy fluxes large enough to be detectable.

• HD 179949 b produces 1020 W if both exoplanet and star have magnetic fields 10 x stronger than Jupiter and sun, respectively.

Parker Model for Properties near 564 Exoplanets

Modelled Energy Flux:HD179949 and companion

TS= 9d, FM = 1010 kg/s, r=0.045 AU, RS=1.19 Rsun, T=107 K, spectral class: F8V