# Planetary Magnetic Field Control of Ion Escape from Weakly Magnetized Planets

## TL;DR

This study uses 3D hybrid simulations to explore how weak planetary magnetic fields influence ion escape, revealing a balance where magnetic strength initially increases escape but then inhibits it, depending on stellar wind conditions.

## Contribution

It demonstrates the complex role of weak magnetic fields in ion escape, providing new insights into planetary atmospheric loss mechanisms and their dependence on magnetic and stellar wind parameters.

## Key findings

- Ion escape rate peaks at an optimal magnetic field strength.
- Stronger magnetic fields can both enhance and inhibit ion escape.
- Power-law relationships describe how escape parameters vary with magnetic field.

## Abstract

Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet's magnetic field enhances ion escape until the magnetic dipole's standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the southern hemisphere from ``misaligned" ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships.