Research

Space plasma turbulence is a complex phenomenon, whose characteristic is the nonlinear cross-scale transfer of turbulent disturbance energy. In the solar wind, the power spectral density of magnetic field fluctuations typically exhibits three distinct power-law intervals, separated by two spectral breaks: the small-scale break marks the transition from magnetohydrodynamic (MHD) scales to ion kinetic scales, while the large-scale break clearly separates the MHD inertial range (corresponding to the frequency interval following an f⁻⁵/³ scaling in the spacecraft frame) from a flatter f⁻¹ scaling regime at larger scales. This characteristic spectral signature is universal and has been observed in the magnetosheaths of multiple planets, including Earth, Mars, Venus, and Saturn. Elucidating the physical nature of turbulent fluctuations is of great significance. Currently, various methods can be employed to separate the relative contributions of different MHD modes and coherent structures from satellite observation parameters. Previous studies have confirmed that a variety of cross-scale fluctuations and plasma coherent structures, such as Alfvén waves, fast/slow magnetosonic waves, filamentary Alfvén vortices, current sheets, and magnetic holes, are key carriers of energy transfer and dissipation processes.

The turbulence in the Martian magnetosheath exhibits unique characteristics that distinguish it from other planetary magnetosheaths, primarily due to its distinct spatial scales and plasma environment. The spatial extent of the Martian magnetosheath is exceptionally compact, only 5%–10% that of Earth’s magnetosheath. This characteristic fundamentally constrains the development of solar wind turbulence processed by the bow shock, potentially directly affecting the spatial evolution of turbulence and its extension to smaller scales. Meanwhile, neutral particles from Martian atmospheric escape generate pickup ions imbued with free energy in the solar wind rest frame through photoionization and charge exchange processes. The local energy injection from these particles can trigger the development of proton cyclotron waves (PCWs) and other wave modes within the Martian magnetosheath. This not only complicates the understanding of cross-scale energy transfer processes but may also significantly enhance the rate of turbulent energy transfer across scales. However, to date, this phenomenon has only been observationally confirmed in regions of PCWs upstream of the Martian bow shock in the solar wind. Currently, systematic and in-depth understanding of the parametric dependencies and spatial evolution of the cross-scale energy transfer rate in Martian magnetosheath turbulence remains lacking, indicating significant gaps in related research.

Recently, the research group lead by Academician Wang Chi from the State Key Laboratory of Solar Activity and Space Weather, in collaboration with researchers from École Polytechnique in France, the University of Buenos Aires in Argentina, and University College London in the UK, conducted a detailed analysis of the solar wind turbulence energy cascade rate near Mars. This analysis was based on years of high-resolution magnetic field and ion data provided by the MAVEN spacecraft, focusing on the evolution of the solar wind turbulence energy cascade rate across the Martian bow shock. For the first time via in situ spacecraft observations, this study characterized the spatial evolution features of the turbulence energy cascade rate at MHD scales and its correlation with bow shock parameters. The key findings reveal that the turbulence energy cascade rate increases by an average of three orders of magnitude during the transition from the solar wind to the magnetosheath. Surprisingly, the turbulence energy cascade rate downstream of oblique and quasi-perpendicular shocks is higher than that observed downstream of quasi-parallel shocks. These results provide the first direct observational evidence for the correlation between shock normal angles and enhanced turbulence energy dissipation, offering important insights into the shock-solar wind turbulence interaction process, which is ubiquitous in space plasmas.

The paper was recently published in the international journal Geophysical Research Letters.

Paper information： Jiang, W., Li, H. Andrés, N., Hadid, L., Verscharen, D., & Wang, C. (2025). Significant amplification of turbulent energy dissipation through the shock  transition at Mars. Geophysical Research Letters, 52, e2025GL117801. https://doi. org/10.1029/2025GL117801

Figure 1. (a) Spatial distribution of the solar wind turbulence energy cascade rate upstream and downstream of the Martian bow shock. (b) Distribution of the solar wind turbulence energy cascade rate as a function of distance from Mars. (c-e) Distributions of the solar wind turbulence energy cascade rate upstream of the bow shock, downstream of the bow shock, and the upstream-to-downstream ratio, respectively, as functions of the shock normal angle.

Figure 2. (a) Distributions of the turbulent Mach number and density fluctuation amplitude in the Martian magnetosheath as functions of the shock normal angle; (b) Statistical distributions of the compressible turbulence energy cascade rate in the solar wind upstream of the Martian bow shock and in the magnetosheath downstream as functions of the turbulent Mach number.