Inhibition of the electron cyclotron maser instability in the dense magnetosphere of a hot Jupiter

TL;DR

This study uses 3D MHD simulations to investigate why hot Jupiters' expected radio emissions via ECMI are not observed, revealing that their expanding atmospheres inhibit ECMI by raising plasma frequencies.

Contribution

The paper demonstrates through simulations that the dense atmospheres of hot Jupiters inhibit ECMI-driven radio emissions, explaining the lack of observational detections.

Findings

ECMI emission is inhibited by planetary atmospheres due to increased plasma frequency.

Simulations predict a radio flux of 0.069 mJy at 10 pc, near detectability limits.

The magnetosphere's properties align with a colliding wind system model.

Abstract

Hot Jupiter (HJ) type exoplanets are expected to produce strong radio emission in the MHz range via the Electron Cyclotron Maser Instability (ECMI). To date, no repeatable detections have been made. To explain the absence of observational results, we conduct 3D adaptive mess refinement (AMR) magnetohydrodynamic (MHD) simulations of the magnetic interactions between a solar type star and HJ using the publicly available code PLUTO. The results are used to calculate the efficiency of the ECMI at producing detectable radio emission from the planets magnetosphere. We also calculate the frequency of the ECMI emission, providing an upper and lower bounds, placing it at the limits of detectability due to Earth's ionospheric cutoff of $\sim 10 \ \mathrm{MHz}$. The incident kinetic and magnetic power available to the ECMI is also determined and a flux of $0.069 \ \mathrm{mJy}$ for an observer at $10 \ \mathrm{pc}$ is calculated. The magnetosphere is also characterized and an analysis of the bow shock which forms upstream of the planet is conducted. This shock corresponds to the thin shell model for a colliding wind system. A result consistent with a colliding wind system. The simulation results show that the ECMI process is completely inhibited by the planets expanding atmosphere, due to absorption of UV radiation form the host star. The density, velocity, temperature and magnetic field of the planetary wind are found to result in a magnetosphere where the plasma frequency is raised above that due to the ECMI process making the planet undetectable at radio MHz frequencies.