Radiation Conditions near Exoplanets of the TRAPPIST-1 System

Abstract

Stellar and galactic cosmic rays (SCR and GCR) are the primary factors influencing the radiation conditions near exoplanets. The GCR spectrum and its time variations are shaped by modulation processes in the astrosphere (the parameters of stellar wind and the local interstellar medium). The estimation of the velocity and density of hot stellar wind in the Parker model demonstrates that their values may change several fold, while the observations reveal that the stellar magnetic fields (and, consequently, the magnetic field of stellar wind) vary by one or two orders of magnitude. Galactic CR may be virtually non-existent near exoplanets of stars with strong magnetic field as a result of the modulation. The radiation conditions are then determined by SCR: the stellar activity, the energy of stellar flares, and the parameters of exoplanet orbits. The estimates of GCR and SCR fluxes near the exoplanets in the habitable zone of the TRAPPIST-1 system, which were obtained using the Parker model and the available data on the stellar magnetic field and activity, are presented below.