Les magnétosphères exoplanétaires dans le domaine radio

Planetary-scale magnetic fields are a window to a planet’s interior and provide shielding of the planet’s atmosphere and surface for life. The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal dynamo currents that generate planetary-scale magnetic fields. When coupled to energetic (keV) electrons, such as those produced by solar windmagnetosphere interaction (compression or magnetic reconnection), magnetosphere-ionosphere or magnetosphere-satellite coupling, the polar regions of a planetary magnetic field are the place of intense, coherent, circularly polarized cyclotron radio emissions. These emissions – that may be as intense as solar ones – are produced by all magnetized planets in the solar system in the MHz range, and up to 40 MHz at Jupiter. Detection of similar emissions from exoplanets will provide constraints on the thermal state, composition, and dynamics of their interior – very difficult to determine by other means – as well as an improved understanding of the planetary dynamo process and of the physics of star-planet plasma interactions.

Detailed knowledge of magnetospheric emissions from solar system planets and the discovery of exoplanets motivated both theoretical and observational work on magnetospheric emissions from exoplanets. Scaling laws and theoretical frameworks were built and extrapolated to obtain orderof- magnitude predictions of frequencies and flux densities of exoplanetary radio emissions. The present stage of the theory suggests that radio detection of exoplanets will develop the new field of comparative exo-magnetospheric physics, but also permit to measure exoplanetary parameters such as rotation or orbit inclination.

Observational searches started even before the confirmed discovery of the first exoplanet. I review the scientific return of the detection of exoplanetary radio emissions, the current status of observational searches with UTR-2 (Ukraine), LOFAR (The Netherlands)), GMRT (India), and discuss the future promise in the context of SKA (especially SKA1- Low that will be able to detect Jupiter-like planets up to about 10 pc) and future space projects.