The first planet outside of our solar system was discovered in 1995. A decade later, more than hundred extrasolar planets had been detected. With the Corot mission having launched at the end of 2006 the exoplanet search is extended by satellite based programs which will significantly increase the detection rate.
Extrasolar planets feature an enormous spectrum of properties. Scenarios that do not appear in our solar system as giant planets orbiting far inside an orbit comparable to Mercury are most spectacular. Thereby, completely new interaction types of the exoplanet with the host star's stellar wind occur.
On the one hand, the planet can be located within the critical points, where the stellar wind reaches sound speed, alfénic speed or magnetoacoustic speed. In this subcritical case, the magnetic communication between star and exoplanet is mutual, while planets of our solar system are all within the supercritical region and they do not permit feedback to the sun. Miscellaneous speculations about possible consequences could be made, up to triggering of superflares at generally "good natured", sun like stars. With magnetohydrodynamic and hybrid models we simulate these scenarios and we investigate their consequences including effects that are potentially detectable from Earth.
The figure shows a MHD simulation of the embedding of a magnetized exoplanet in a subcritical stellar wind. Stellar magnetic field lines (green), closed magnetic field lines remaining at the exoplanet (red) and magnetic field lines connecting the star and the exoplanet (blue) are shown. [Figure: Sabine Preusse, Dissertation TU Braunschweig, 2005].
On the other hand, the energy input by the stellar wind into the plasma environment or the magnetosphere of an exoplanet can be much larger compared to our solar system. Therefore extrasolar planets might become such strong radio sources that their radiation can be potentially observed on Earth. The radio array LOFAR being under construction is very promising. Its final sensitivity is expected to be sufficient to detect exoplanets by their radio emission.
References
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Johansson, E.P.G., J. Mueller, and U. Motschmann Quasiparallel and parallel stellar wind interaction and the magnetospheres of close-in exoplanets, Astronomische Nachrichten, doi: 10.1002/asna.201111626, 2011.
Johansson, E.P.G., J. Mueller, and U. Motschmann Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets, Astronomy and Astrophysics, 10.1051/0004-6361/201014802, 2011.
Johansson, E.P.G., J. Mueller, and U. Motschmann Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets, Astronomy and Astrophysics, 10.1051/0004-6361/201014802, 2011.
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