Resistive MHD Simulations of Stellar Wind-Magnetosphere Coupling in TRAPPIST-1e

Close-in terrestrial exoplanets around M dwarfs reside in dense, magnetized winds, where non-ideal plasma coupling can strongly affect how electromagnetic energy is redistributed within the dayside interaction region.

We present three-dimensional resistive magnetohydrodynamic simulations of the TRAPPIST-1 wind interacting with a dipolar TRAPPIST-1e magnetosphere for three stellar-wind forcing cases and four prescribed magnetic diffusivities, η=(0, 538.018, 5.38018×10⁸, 5.38018×10¹²) cm² s⁻¹.

Energy transport is diagnosed using maps of the total energy density, the magnitude of the total Poynting flux, and the divergence of the total Poynting flux. We further estimate a radio-power proxy from the volume integral of ∇⋅Stotal over the dayside bow-shock and magnetopause layers.

Across all cases, increasing prescribed η broadens the coupling layer and shifts the dominant energy-conversion regions from thin, patchy boundary arcs to thicker, more spatially extended structures, with an increasing relative contribution from the magnetopause. The inferred radio-power proxy increases by several orders of magnitude across the explored scan.

However, because the estimated numerical magnetic diffusivity in the strongest-gradient regions is ηnum∼10¹⁵-10¹⁶ cm² s⁻¹, the present η scan is best interpreted as a controlled sensitivity study rather than as a direct constraint on the physical diffusivity of the TRAPPIST-1e environment.

For the adopted planetary fields (B_eq=0.32-1.28 G), the maximum cyclotron frequencies are νc,max≈1.8-7.2 MHz, below the ground-based window, implying that meaningful radio constraints on TRAPPIST-1e magnetism will require space-based observations below 10 MHz or substantially stronger planetary fields than those assumed here.

Case #2. Equatorial-plane maps of mass density 𝜌 (panels a and d; g cm⁻³ ) and dynamic pressure 𝑝dyn (panels b and e; dyn cm⁻² ), with magnetic field lines overplotted in black. Panels c and f show meridional-plane maps of 𝜌 at 𝑥 = 1.5 𝑅_p. The top row corresponds to 𝜂 = 0 cm²s ⁻¹, and the bottom row to 𝜂 = 5.38018 × 10¹²cm² s⁻¹ .

J.J. González-Avilés, N. Baltazar Pérez-Negrón, A. Segura

Comments: 10 pages, 6 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2604.00191 [astro-ph.EP] (or arXiv:2604.00191v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.00191
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From: J.J. González-Avilés
[v1] Tue, 31 Mar 2026 19:47:22 UTC (5,788 KB)
https://arxiv.org/abs/2604.00191
Astrobiology, Exoplanet, Space Weather,