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,\ 5.380\,18× 10⁸,\ 5.380\,18× 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 η ₙᵤₘ~ 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 (Beq=0.32–1.28 G), the maximum cyclotron frequencies are ν c,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.