# Occultations of astrophysical radio sources as probes of planetary environments: A case study of Jupiter and possible applications to exoplanets

## TL;DR

This study investigates using occultations of distant astrophysical radio sources to measure planetary environments, demonstrating potential for Jupiter and suggesting applications for exoplanets, with implications for remote sensing of planetary atmospheres and magnetic fields.

## Contribution

It introduces a novel method of probing planetary magnetic fields and atmospheres via astrophysical radio source occultations, expanding beyond traditional spacecraft-based techniques.

## Key findings

- Significant polarization changes due to Faraday rotation near Jupiter
- Detectable frequency and power variations from neutral atmospheres
- Occultations are likely to occur at least once per year for suitable sources

## Abstract

Properties of planetary atmospheres, ionospheres, and magnetospheres are difficult to measure from Earth. Radio occultations are a common method for measuring these properties, but they traditionally rely on radio transmissions from a spacecraft near the planet. Here we explore whether occultations of radio emissions from a distant astrophysical radio source can be used to measure magnetic field strength, plasma density, and neutral density around planets. In a theoretical case study of Jupiter, we find that significant changes in polarization angle due to Faraday rotation occur for radio signals that pass within 10 Jupiter radii of the planet and that significant changes in frequency and power occur from radio signals that pass through the neutral atmosphere. There are sufficient candidate radio sources, such as pulsars, active galactic nuclei, and masers, that occultations are likely to occur at least once per year. For pulsars, time delays in the arrival of their emitted pulses can be used to measure plasma density. Exoplanets, whose physical properties are very challenging to observe, may also occult distant astrophysical radio sources, such as their parent stars.