# Magnetic field strengths of hot Jupiters from signals of star-planet interactions

## TL;DR

This study estimates magnetic field strengths of hot Jupiters through star-planet interaction signals, revealing stronger fields than some models predict and suggesting potential radio emissions detectable via further observations.

## Contribution

It provides the first direct estimates of hot Jupiter magnetic fields using chromospheric emission data, challenging existing dynamo predictions and supporting internal heat flux scaling laws.

## Key findings

- Magnetic fields range from 20 G to 120 G.
- Field strengths are 10-100 times larger than dynamo law predictions.
- Potential for observable radio emissions due to strong magnetic fields.

## Abstract

Evidence of star-planet interactions in the form of planet-modulated chromospheric emission has been noted for a number of hot Jupiters. Magnetic star-planet interactions involve the release of energy stored in the stellar and planetary magnetic fields. These signals thus offer indirect detections of exoplanetary magnetic fields. Here we report the derivation of the magnetic field strengths of four hot Jupiter systems using the power observed in Ca II K emission modulated by magnetic star-planet interactions. By approximating the fractional energy released in the Ca II K line we find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, ~10-100 times larger than the values predicted by dynamo scaling laws for planets with rotation periods of ~2 - 4 days. On the other hand, these value are in agreement with scaling laws relating the magnetic field strength to the internal heat flux in giant planets. Large planetary magnetic field strengths may produce observable electron-cyclotron maser radio emission by preventing the maser from being quenched by the planet's ionosphere. Intensive radio monitoring of hot Jupiter systems will help confirm these field values and inform on the generation mechanism of magnetic fields in this important class of exoplanets.