Pickup Ion Modulation on Plateau-like Turbulence in the Martian Magnetosheath

Abstract

Abstract The distribution of magnetic energy across scales, represented by the turbulence spectrum, provides insights into magnetic field dynamics in astrophysical and space plasma. While the Earth’s magnetosheath exhibits a conventional two-slope spectrum, the Martian magnetosheath often displays a prominent plateau-like spectrum. However, the underlying physical mechanism remains unresolved. Based on MAVEN observations, we present appealing evidence of pickup ions (PUIs) modulating the plateau-like spectrum through proton cyclotron waves (PCWs). PCWs, driven by unstable pickup H+ ion distributions, significantly influence the formation of plateau-like spectra. Both case and statistical studies suggest that the spectral evolution is affected by the relative abundance of pickup O+ ions. A substantial presence of pickup O+ ions can suppress PCWs driven by pickup H+ ions, resulting in a decline in the slope of the plateau spectrum. Particle-in-cell simulations confirm the role of PUI-modulated PCWs in the plateau-range energy injection. Our results provide new insight into the impact of PUIs on magnetic turbulence evolution and associated energy transfer processes in space and astrophysical plasma.