Comparison of Alfvén speed and Alfvénic Mach number profiles in SPMI and the Jovian system. Panel a shows the Alfvén speed distribution in our simulated SPMI system. The red curve traces a magnetic field line from an exoplanet at 5 stellar radii to the star. Panel b presents a meridional slice of Alfvén speed within Jupiter’s magnetosphere, highlighting the localized influence of the Io plasma torus. The blue and green lines mark magnetic field lines traced from the Io and Ganymede orbits, respectively. Panel c plots the Alfvén speed along these field lines and panel d shows the corresponding Alfvénic Mach number profiles along the field lines.