Modelling the imposed magnetospheres of Mars-like exoplanets: star–planet interactions and atmospheric losses

Abstract

Based on 3D compressible magnetohydrodynamic (MHD) simulations, we explore the interactions between the magnetized wind from a solar-like star and a Mars-like planet – with a gravitionally stratified atmosphere – which is either non-magnetized or hosts a weak intrinsic dipolar field. The primary mechanism for the induction of a magnetosphere around a non-magnetized conducting planet is the pile-up of stellar magnetic fields in the day side region. The magnetopause stand-off distance decreases as the strength of the planetary dipole field is lowered and saturates to a minimum value for the case of a planet with no magnetic field. Global features such as bowshock, magnetosheath, magnetotail and strong current sheets are observed in the imposed magnetosphere. We explore variations in atmospheric mass loss rates for different stellar wind strengths to understand the impact of stellar magnetic activity and plasma winds – and their evolution – on (exo)planetary habitability. In order to simulate a case analogous to the present-day Mars, a planet without atmosphere is considered. The results are found to be in good agreement with observational data from Mars missions such as MGS and MAVEN.

Exoplanet Radio Transits as a Probe for Exoplanetary Magnetic Fields—Time-dependent MHD Simulations

“…When we perform the simulation with a non-magnetized planet, we find an induced magnetosphere around the nonmagnetized planet (see Figure 5). This reaffirms previous findings (Stevenson 2003;Ma et al 2013;Basak & Nandy 2021) that non-magnetized planet possess an induced magnetosphere. Figure 5 shows the density modulations of the surrounding medium due to the induced magnetosphere when the planet is non-magnetized.…”

“…In our solar system, interaction between the solar wind and the Venus atmosphere is an ideal example of such an unipolar interaction. It was shown that the unipolar interaction leads to the creation of an induced magnetosphere having similar global structure like other self-generated planetary magnetosphere (e.g., Luhmann et al 1981;Kivelson & Russell 1995;Russell et al 2006;Basak & Nandy 2021). However, (e.g., Ma et al 2013) have shown that induced magnetosphere has much less spatially extended compared to the self-generated planetary magnetoshpere.…”

“…This figure indicates that the size of the planetary magnetosphere is larger for the higher planetary magnetic field. Kivelson & Russell 1995;Russell et al 2006;Basak & Nandy 2021). However, Ma et al (2013) have shown that the induced magnetosphere was much less spatially extended compared to the self-generated planetary magnetosphere.…”

Mean field models of flux transport dynamo and meridional circulation in the Sun and stars

“…The global magnetic field distribution in the Sun and stars, its parity, and the structure of coronal magnetic fields are governed by the dynamo mechanism (Dash et al, 2023) and surface emergence and evolution of magnetic flux (Nandy et al, 2018;Kavanagh et al, 2021). The magnetic field topology in turn determines the global stellar magnetosphere and magnetized stellar wind (Réville et al, 2015;Vidotto et al, 2014b) that play critical roles in star-planet interactions (Das et al, 2019;Basak and Nandy, 2021;Carolan et al, 2021) and the forcing of (exo)planetary space environments (Nandy et al, 2021;Hazra et al, 2022). Also, the stellar magnetic cycle alters the total X-ray and EUV (XUV) radiation from host stars affecting exoplanetary atmospheres (Hazra et al, 2020).…”

Impact of Changing Stellar and Planetary Magnetic Fields on (Exo)planetary Environments and Atmospheric Mass Loss

“…Gravitational (tidal) interactions can be neglected if the planet lies far away (as in the case for Sun-Earth system) and in such a scenario, the stellar wind independently affects the planetary environment without the possibility of the coronal structure of the star getting modified. The evolution of planetary atmospheres and the nature of its interaction with the stellar wind are profoundly affected by changes in their respective magnetic field strengths (Cohen et al 2015;Basak & Nandy 2021). Discovery of several exoplanets (Mayor & Queloz 1995;Pepe et al 2014;Lunine et al 2009) has sparked interest in exploring the signatures of life-sustaining conditions and understanding habitability from the perspective of the origin and evolution of planetary atmospheres (Lammer et al 2009;Lammer 2013;Pollack & Yung 1980;Cridland et al 2017).…”