SO webloquio: Star-planet plasma interactions and radio emissions

Exoplanets are expected to sustain various plasma interactions with their parent star, depending on the stellar and planetary magnetic field strengths and on the sub- or super-Alfvénic wind speed at the planet’s orbit. Three such interactions lead to electron acceleration and subsequent radio emissions in our solar system: magnetized planets hit by the super-Alfvénic solar wind, and the sub-Alfvénic interactions of the unmagnetized moon Io and and the magnetized moon Ganymede with Jupiter’s rotating magnetosphere. The resulting radio emissions are all produced by the cyclotron Maser (CM) instability. I will present the main properties of solar system CM radio emissions before summarizing the CM theory, that is at an advanced enough stage for providing a remote sensing tool of exoplanet’s magnetic field, rotation, plasma environment, orbit inclination, and interaction (type and energetics) with its parent star, provided that radio emission intensity and polarization are detected with a reasonable SNR in the time-frequency domain. Without knowing electron distributions in the sources, that can only be obtained via in-situ measurements, it is not possible to predict radio emission intensity from basic plasma physics. But I showed that solar system radio emissions follow a scaling law that relates the emitted radio power to the Poynting flux dissipated in the star-planet interaction. Extrapolated to known exoplanets, this law predicts high levels of radio emission for the ones orbiting close to their parent star, susceptible to be detected by large existing radio telescopes and arrays. I will give a brief overview of the radio detections to date, and prospects for the near future. Finally, I will propose a general framework for classifying start-planet plasma interactions, that includes the types observed in the solar system as well as yet unobserved predictions, and is perhaps even applicable to the elusive fast radio bursts.

21/06/2022 - 12:30
Dr. Philippe Zarka
Observatoire de Paris