Stellar energetic particles in the magnetically turbulent habitable zones of TRAPPIST-1-like planetary systems

Abstract

Planets in close proximity to their parent star, such as those in the habitable zones around M dwarfs, could be subject to particularly high doses of particle radiation. We have carried out test-particle simulations of ~GeV protons to investigate the propagation of energetic particles accelerated by flares or travelling shock waves within the stellar wind and magnetic field of a TRAPPIST-1-like system. Turbulence was simulated with small-scale magnetostatic perturbations with an isotropic power spectrum. We find that only a few percent of particles injected within half a stellar radius from the stellar surface escape, and that the escaping fraction increases strongly with increasing injection radius. Escaping particles are increasingly deflected and focused by the ambient spiralling magnetic field as the superimposed turbulence amplitude is increased. In our TRAPPIST-1-like simulations, regardless of the angular region of injection, particles are strongly focused onto two caps within the fast wind regions and centered on the equatorial planetary orbital plane. Based on a scaling relation between far-UV emission and energetic protons for solar flares applied to M dwarfs, the innermost putative habitable planet, TRAPPIST-1e, is bombarded by a proton flux up to 6 orders of magnitude larger than experienced by the present-day Earth. We note two mechanisms that could strongly limit EP fluxes from active stars: EPs from flares are contained by the stellar magnetic field; and potential CMEs that might generate EPs at larger distances also fail to escape.

17 pages, 12 figures, ApJ in press

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Cited by in corpus (19)

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• The High-Energy Radiation Environment Around a 10 Gyr M Dwarf: Habitable at Last?
• A review of possible planetary atmospheres in the TRAPPIST-1 system
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• Accounting for Multiplicity in Calculating Eta Earth
• A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection
• Evryscope and K2 Constraints on TRAPPIST-1 Superflare Occurrence and Planetary Habitability
• Stellar versus Galactic: The intensity of cosmic rays at the evolving Earth and young exoplanets around Sun-like stars
• Stellar Winds Drive Strong Variations in Exoplanet Evaporative Outflows and Transit Absorption Signatures
• Stellar Proton Event-induced surface radiation dose as a constraint on the habitability of terrestrial exoplanets
• The Earth-like Galactic cosmic ray intensity in the habitable zone of the M dwarf GJ 436
• The Space Environment and Atmospheric Joule Heating of the Habitable Zone Exoplanet TOI700-d
• The energetic particle environment of a GJ 436 b-like planet
• Revisiting Empirical Solar Energetic Particle Scaling Relations I. Solar flares
• Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU~Microscopii
• Galactic cosmic ray propagation through M dwarf planetary systems
• Under the magnifying glass: A combined 3D model applied to cloudy warm Saturn type exoplanets around M-dwarfs
• Connecting Solar and Stellar Flares/CMEs: Expanding Heliophysics to Encompass Exoplanetary Space Weather
• A huge-amplitude white-light superflare on a L0 brown dwarf discovered by GWAC survey