Solar Orbiter encounters an unusually high Mach number interplanetary shock

¹ Swedish Institute of Space Physics, Uppsala, Sweden
² Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
³ ESA ESAC, Madrid, Spain
⁴ Northumbria University, Newcastle, UK
⁵ Queen Mary University of London, London, UK

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 11 December 2025
Accepted: 23 February 2026

Abstract

Aims. The objective of this study is to characterise and understand the magnetic structure of an extremely high Mach number interplanetary shock.

Methods. We analysed magnetic field and plasma data from Solar Orbiter during the shock crossing and compared them with high-resolution MMS observations and results from a hybrid particle-in-cell (PIC) shock simulation. Shock profiles, magnetic overshoots, and upstream wave activity were examined across all datasets.

Results. Solar Orbiter measured an exceptionally large magnetic amplification (B_max/B_u ∼ 10), though the magnitude was highly sensitive to the instrument sampling rate. No clear evidence of ion reflection or whistler precursors (expected for such high Mach numbers) was observed by Solar Orbiter. In contrast, MMS and simulation data revealed complex spatial and temporal structures that were not resolvable by Solar Orbiter. The hybrid PIC model reproduces several global shock features, but its agreement with observations depends strongly on the chosen spatial cut and simulation time step. Upstream Langmuir waves were observed without signs of a sustained electron foreshock, implying intermittent magnetic connectivity and a distorted shock surface.

Conclusions. The results suggest that high Mach number interplanetary shocks possess substantial non-stationary and fine-scale structure, but their rapid motion and limited in situ sampling make these features difficult to resolve. Accurate interpretation therefore requires coordinated analyses using multi-mission observations and numerical simulations.