Super-CMEs, solar-like particle storms: How a young Sun's strong magnetic field tames its energetic particles

The atmospheric evolution of exoplanets is shaped not only by radiation, but also by stellar energetic particles (EPs) that drive ionization, photochemistry and additional atmospheric escape. However, for planets orbiting active young stars, current estimates rely on extrapolating solar EP observations, which usually believe stronger stellar eruptions would lead to order-of-magnitude stronger EPs. Here we present the first global 3D simulations of EP events driven by stellar coronal mass ejection (CME) shocks from EK Draconis, a young solar-type star (G1.5V, $\sim$100 Myr, P_rot=2.8 days) with observational constraints on magnetic activity and eruptions. We employ the Space Weather Modelling Framework (SWMF) coupled with the Multiple Field-Line Advection Model for Particle Acceleration (M-FLAMPA), a state-of-the-art module validated against solar EP events. The simulated CMEs with kinetic energies of $10^{33}-10^{35}$ erg and mean radial speeds of 3000 and 10000 $kms^{-1}$, drive shocks that accelerate protons to high energies. The peak differential intensities at 1au shows similar values as typical solar EP events at energies above 10 MeV. This is because the stronger magnetic fields make the strong-shock condition harder to satisfy, so that even the fast stellar CMEs drive shocks with properties similar to those of solar CMEs. The tightly wound Parker spiral imposed by rapid stellar rotation produces energy- and latitude-dependent EP onset timings, such that planets at different orbital inclinations and distances would experience markedly different particle radiation histories. By delivering spatially and temporally resolved EP spectra at planetary distances, our results offer essential input for atmospheric chemistry and escape models of young exoplanets, complementing XUV irradiation estimates.