# Role of planetary obliquity in regulating atmospheric escape: G-dwarf vs. M-dwarf Earth-like exoplanets

## TL;DR

This study uses a multi-fluid MHD model to assess how planetary obliquity affects atmospheric escape rates on Earth-like exoplanets, finding a weak influence around G-dwarfs but a significant impact around M-dwarfs.

## Contribution

It introduces a detailed multi-fluid MHD model to quantify atmospheric ion losses considering planetary obliquity effects on different star types.

## Key findings

- Weak dependence of escape rates on obliquity for G-dwarf planets.
- Obliquity can alter escape rates by over 200% for M-dwarf planets.
- Atmospheric retention is moderately influenced by planetary obliquity.

## Abstract

We present a three-species (H$^+$, O$^+$ and e$^-$) multi-fluid magnetohydrodynamic (MHD) model, endowed with the requisite upper atmospheric chemistry, that is capable of accurately quantifying the magnitude of oxygen ion losses from "Earth-like" exoplanets in habitable zones, whose magnetic and rotational axes are roughly coincidental with one another. We apply this model to investigate the role of planetary obliquity in regulating atmospheric losses from a magnetic perspective. For Earth-like exoplanets orbiting solar-type stars, we demonstrate that the dependence of the total atmospheric ion loss rate on the planetary (magnetic) obliquity is relatively weak; the escape rates are found to vary between $2.19 \times 10^{26}$ s$^{-1}$ to $2.37 \times 10^{26}$ s$^{-1}$. In contrast, the obliquity can influence the atmospheric escape rate ($\sim$ $10^{28}$ s$^{-1}$) by more than a factor of $2$ (or $200\%$) in the case of Earth-like exoplanets orbiting late-type M-dwarfs. Thus, our simulations indicate that planetary obliquity may play a weak-to-moderate role insofar as the retention of an atmosphere (necessary for surface habitability) is concerned.