Theoretical Concepts of Electromagnetic Star-Planet Interaction

Most exoplanets are expected to be embedded in the flows of plasmas and magnetic fields from their host stars. If the exoplanets are sufficiently close to their host stars such that the wave modes generated at the exoplanets can travel back to the star, then both bodies electromagnetically couple. This coupling is referred to as electromagnetic star-planet interaction (SPI)Electromagnetic star-planet interaction (SPI) and can result in large electromagnetic energy fluxesElectromagnetic Energy Fluxes between the exoplanets and the stars possibly generating luminous effects on the stars. The root cause of the electromagnetic interaction is the relative motion of the exoplanet with respect to the magnetized plasma of the stellar wind of the host star. Due to the large diversity of exoplanets, e.g., distance to the star, size, and the diversity of the host stars, e.g., spectral classes, the energy fluxes in the star planet interaction are expected to exhibit huge qualitative and quantitative differences. This chapter introduces the basic setup of this coupling and the underlying physical mechanisms. Various models of the coupling are discussed, such as the Alfvén wing modelAlfvén wing model or models which describe the release of magnetic stressesRelease of magnetic stresses, e.g., in coronal magnetic fieldsCoronal magnetic fields. The chapter also briefly reviews the existing observational evidence for star planet interaction and puts it in context with theoretical expectations. Additionally, star planet interaction is compared with the well-studied electromagnetic coupling between planets and moons in the outer solar system, e.g., Jupiter and its moon Io.