2025ApJ...994...75S

Recent multiwavelength observations of young solar analogs suggest that the young Sun in the first 600 Myr was a magnetically active star that produced an X-ray and extreme-UV bright corona, fast, massive stellar wind, and energetic eruptive events. These outputs affected the magnetospheric environments of the early Earth and young rocky exoplanets. The interaction of the fast solar wind with the slow wind produced strong shocks from corotating interaction regions (CIRs) that provided high dynamic pressure on the magnetospheres of early Venus, Earth, and Mars. Here, we apply the Space Weather Modeling Framework, coupled with the Rice Convection Model, to simulate the response of the magnetospheric environments and associated Joule heating deposited in the upper atmosphere of the early Earth as it passed through a CIR shock from the young Sun. The model suggests a ∼40% closer dayside magnetopause standoff distance, and higher negative SYMH, cross polar cap potentials, atmospheric Joule heating, field-aligned currents, electron precipitations, and equatorward polar cap expansions, comparable to or exceeding those of recent intense and super geomagnetic storms. The magnetic storm produces dawn-dusk asymmetries in the polar cap boundary arising from the stellar magnetic field B_y. The proton density enhancements during the CIR event are the dominant factor in the overall dynamic pressure for resulting electron precipitation and Joule heating deposited into the Earth's ionosphere. We discuss implications for the magnetospheric states and associated habitability conditions on the early Earth and young rocky exoplanets around magnetically active solar-like stars.