EAS Publications Series
Volume 29, 2008Tidal Effects in Stars, Planets and Disks
|Page(s)||245 - 273|
|Published online||20 June 2008|
M.-J. Goupil and J.-P. Zahn (eds)
EAS Publications Series, 29 (2008) 245-273
Plasma interactions of exoplanets with their parent star and associated radio emissions
LESIA, Observatoire de Paris–CNRS–UPMC–Univ. Paris Diderot, 92190 Meudon, France
The relatively high contrast between planetary and solar low frequency radio emissions suggests that the low–frequency radio range may be well adapted to the direct detection of exoplanets. We review the most significant properties of planetary radio emissions (auroral as well as satellite–induced) and show that their primary engine is the interaction of a plasma flow with an obstacle in the presence of a strong magnetic field (of the flow or of the obstacle). Scaling laws have been derived from solar system planetary radio emissions that relate the emitted radio power to the power dissipated in the various corresponding flow–obstacle interactions. We generalize these scaling laws into a “radio–magnetic” scaling law that seems to relate output radio power to the magnetic energy flux convected on the obstacle, this obstacle being magnetized or unmagnetized. Extrapolating this scaling law to the case of exoplanets, we find that hot Jupiters may produce very intense radio emissions due to either magnetospheric interaction with a strong stellar wind or to unipolar interaction between the planet and a magnetic star (or strongly magnetized regions of the stellar surface). In the former case, similar to the magnetosphere–solar wind interactions in our solar system or to the Ganymede–Jupiter interaction, a hecto–decameter emission is expected in the vicinity of the planet with an intensity possibly 103 to 105 times that of Jupiter's low frequency radio emissions. In the latter case, which is a giant analogy of the Io–Jupiter system, emission in the decameter–to–meter wavelength range near the footprints of the star's magnetic field lines interacting with the planet may reach 106 times that of Jupiter (unless some “saturation” mechanism occurs). The system of HD 179949, where a hot spot has been tentatively detected in visible light near the sub–planetary point, is discussed in some details. Finally, we discuss the interests of direct radio detection, among which access to exoplanetary magnetic field measurements and comparative magnetospheric physics.
© EAS, EDP Sciences, 2008
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