Bridging observations and simulations: challenges in planetary bow shock studies

Planetary bow shocks provide an excellent laboratory for studying shock physics. Over the past six decades, they have been extensively investigated in situ by various satellite missions aiming to study particle behavior and fields at both macro and micro scales. Despite significant progress, in situ measurements are limited to the spacecraft’s trajectory, providing only a partial description of the shock’s 3D structure. To address this problem, we can combine these measurements with kinetic plasma simulations, which can significantly enhance our understanding of shock physics. Fully kinetic methods, such as Particle-in-Cell (PIC) simulations, have the capability to describe the evolution of shocks at ion scales while also resolving the dynamics of electrons. However, to cover the necessary spatial and temporal scales, PIC simulations often require the use of unrealistic numerical parameters, such as artificially high shock velocities and reduced ion-to-electron mass ratios. These approximations introduce additional challenges because various aspects of shock microphysics—such as parameters of driven instabilities, heating mechanisms, and particle acceleration—exhibit distinct dependencies on these numerical parameters. This discrepancy complicates direct comparisons between PIC simulations and in situ measurements. To mitigate these issues, rescaling procedures tailored to specific phenomena are necessary. Here, we address the problems of magnetic field amplification, electron heating, and electrostatic waves, each requiring its own distinct set of rescaling procedures.