Acceleration of Electrons in Plasmospheres of Hot Jupiter-Type Exoplanets with a Relatively Weak Magnetic Field

Abstract

In analogy with the acceleration mechanism implemented in the Jupiter–Io system, the electron acceleration mechanism is discussed with the example of the plasmasphere of exoplanet HD 189733b. Under conditions when the oncoming stellar wind flow with the stellar magnetic field included in it reaches a region of the atmosphere with a sufficient number of neutral particles, the different frequencies of collisions of stellar electrons and ions with neutrals ensure charge separation and the emergence of an electric field of charge separation. In this process, an important role is played by the anisotropy of the conductivity of the exoplanet’s plasmasphere, which ultimately leads to a powerful electric field, that has a projection on the direction of the magnetic field and causes electron acceleration. The characteristic energies and fluxes of accelerated electrons for exoplanet HD 189733b are estimated. The possibilities of this acceleration mechanism are discussed from the viewpoint of the occurrence of plasma instability in the atmosphere of the exoplanet and generation of a radio emission flux necessary for recording on Earth. A conclusion is drawn about the energy sufficiency of the proposed acceleration mechanism for observing the radio emission of this exoplanet. The possibilities of implementing the electron acceleration mechanism described above for the other two most studied hot Jupiter-type exoplanets—WASP 12 b and HD 209458 b—are also discussed.