# Ohmic heating in the upper atmosphere of hot exoplanets The influence of a time-varying magnetic field

**Authors:** A. Strugarek, A. García Muñoz, A. S. Brun, A. Paul  
**arXiv:** [2412.14072](https://arxiv.org/abs/2412.14072)  
**Date:** 2024-12-18  
**Summary page:** https://www.summarizepaper.com/en/paper/2412.14072v1/

## Key points

- Study conducted by A. Strugarek, A. García Muñoz, A. S. Brun, and A. Paul on Ohmic heating in the upper atmosphere of hot exoplanets
- Close-in exoplanets exposed to intense X-ray and ultraviolet (XUV) radiation leading to significant atmospheric heating
- Ohmic heating induced by variations in strong magnetic fields present in surrounding stellar wind
- Aim to quantify impact of Ohmic heating on upper atmospheres of hot exoplanets due to external time-varying magnetic fields and compare with XUV heating
- Ohmic heating heavily dependent on conductivity properties of upper atmosphere; developed 1D formalism for evaluation based on conductivity profiles
- Ohmic heating can reach values as high as 10$^{-3}$ erg s$^{-1}$ cm$^{-3}$ in upper regions of hot exoplanet atmospheres like Trappist-1 b and $\pi$ Men c
- More pronounced for planets closer to host stars and orbiting lower-mass central stars due to increased ambient magnetic field strength
- Crucial role of Ohmic heating in shaping thermal characteristics of hot exoplanet atmospheres; can surpass XUV heating under favorable conditions
- Strong Ohmic heating shields upper atmosphere from time-varying external magnetic fields, preventing deeper penetration into planetary system

## Summary

The study "Ohmic heating in the upper atmosphere of hot exoplanets: The influence of a time-varying magnetic field," conducted by A. Strugarek, A. García Muñoz, A. S. Brun, and A. Paul, delves into the complex interplay of factors affecting the thermal budget of close-in exoplanets. These planets orbit closely around their host stars and are exposed to intense X-ray and ultraviolet (XUV) radiation, resulting in significant atmospheric heating. However, beyond XUV irradiation, these exoplanets also experience Ohmic heating induced by variations in the strong magnetic fields present in the surrounding stellar wind. The researchers aim to quantify the impact of Ohmic heating on the upper atmospheres of hot exoplanets due to external time-varying magnetic fields and compare it with XUV heating. They emphasize that Ohmic heating is heavily dependent on the conductivity properties of the upper atmosphere and develop a 1D formalism to evaluate its level and localization based on conductivity profiles. Through their analysis focusing on specific cases such as Trappist-1 b and $\pi$ Men c, the team finds that Ohmic heating can reach values as high as 10$^{-3}$ erg s$^{-1}$ cm$^{-3}$ in these hot exoplanet atmospheres' upper regions. Importantly, they note that this type of heating tends to be more pronounced for planets closer to their host stars and orbiting lower-mass central stars due to increased ambient magnetic field strength. The study confirms that Ohmic heating plays a crucial role in shaping the thermal characteristics of hot exoplanet atmospheres and can even surpass XUV heating under favorable conditions. Additionally, they highlight a significant corollary - strong Ohmic heating effectively shields the upper atmosphere from time-varying external magnetic fields, preventing their penetration deeper into the planetary system. Overall, this research underscores the importance of considering multiple sources of atmospheric heating when studying exoplanetary environments and suggests that both Trappist-1b and $\pi$ Men c are likely experiencing intense levels of Ohmic heating in their upper atmospheres.