The impact of stellar winds and tidal locking effects on the habitability of Earth-like exoplanets around M dwarf stars

TL;DR

This study assesses how stellar wind pressures and tidal locking influence the magnetic protection of Earth-like exoplanets around M dwarfs, highlighting challenges in maintaining Earth-like magnetospheres.

Contribution

It provides a comprehensive analysis of stellar wind effects, including magnetic and ram pressures, on exoplanet magnetospheres considering tidal locking and magnetic field deviations.

Findings

Ram pressure dominates for stars with mass < 0.15 M_sun.

Half of the outer habitable zone planets can sustain early Earth-like magnetospheres.

Deviations from Parker spiral can significantly reduce magnetosphere size.

Abstract

We present an assessment of the effects of stellar wind magnetic and mechanical components on the habitability of Earth-like exoplanets orbiting the inner and outer radii of the habitable zone (HZ) of M dwarfs. We consider stars with masses in the range of $0.09 - 0.75 M_\odot$ and planets with a surface dipolar magnetic field of 0.5 G. We estimate the size of the magnetospheres of such exoplanets using the pressure balance equation including the contribution of magnetic and ram pressures from stellar winds. We explore different scenarios, including fast and slow stellar winds, to assess the relevance of kinetic contribution. Furthermore, the effect of tidal locking and potential deviations from the Parker spiral, typically used to describe the interplanetary magnetic field, are analyzed. We show that for low mass stars ($M < 0.15 M_\odot$), the ram pressure exerted by stellar winds affects the size of the magnetosphere more than the stellar wind magnetic pressure. Interestingly, when the ram pressure is not much stronger than the magnetic pressure, typically for higher mass stars, the inclusion of ram pressure can be beneficial to the magnetosphere due to the magnetopause currents. A magnetosphere with the size of that of modern Earth is difficult to achieve with the current assumptions. However, an early Earth magnetosphere is achieved by roughly half of our hypothetical planets orbiting the outer radius of the HZ in most of the considered cases. We find that deviations from the Parker spiral can affect the results significantly, reducing the magnetosphere by $56\%$ in extreme cases. Most of the hypothetical planets are most likely (or might be) tidally locked, with the notable exception of those orbiting the outer HZ of GJ 846 and V1005 Ori.