Effect of Solar Wind Turbulence on Temperature‐Anisotropy‐Driven Modes in Mercury's Magnetosheath

Abstract Planetary magnetosheaths are plasma regions between the solar wind and planetary magnetospheres where temperature anisotropies act as a source of free energy driving plasma instabilities. While these instabilities have been extensively studied at Earth, their properties at Mercury remain poorly investigated. To support the science goals of the ongoing BepiColombo mission, we investigate the development of ion temperature anisotropy throughout Mercury's magnetosheath using the first global hybrid particle‐in‐cell simulations of the Hermean plasma environment under turbulent solar wind conditions. We employ the 3D hybrid PIC code Menura to model Mercury's magnetosphere for both laminar and turbulent upstream states and classify magnetosheath regions by local bow‐shock geometry (quasi‐parallel, quasi‐perpendicular, and intermediate). The simulations reveal strong spatial variations in plasma stability, with quasi‐perpendicular sectors showing enhanced occurrence of mirror‐mode and ion‐cyclotron unstable plasma. Turbulent solar wind produces a dayside magnetosheath that is, on average, more unstable than in laminar case, while the nightside becomes comparatively more stable. These results demonstrate that upstream solar wind turbulence plays a role in regulating anisotropy‐driven instabilities in Mercury's magnetosheath and should be accounted for in the interpretation of in situ BepiColombo observations.