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Mirror-mode (MM) structures, characterized by intermittent sharp depressions or enhancements of magnetic magnitude, are key plasma-instability-driven phenomena and commonly observed in high-β and temperature-anisotropic space plasmas. Although MM structures have been well studied in Earth’s magnetosheath, their properties in Jupiter’s magnetosheath remain poorly understood due to the limited spatial and temporal coverage of previous missions. Here, by using Juno observations, we present the first comprehensive statistical analysis of MM structures in Jupiter’s magnetosheath. We investigate their spatial distribution and occurrence rate across a broad range of latitudes, thereby clarifying their global spatial characteristics. In addition, we examine the electron pitch-angle distributions associated with MM events to explore particle behavior and possible wave–particle interactions within these structures. These results advance our understanding of the formation and evolution of MM structures in giant planetary magnetosheaths and their related electron dynamics in Jupiter’s magnetosheath.

Electromagnetic ion cyclotron (EMIC) waves and mirror modes (MMs), both driven by ion temperature anisotropy, are commonly observed in planetary magnetosheaths. Conventional explanations for their co‐occurrence are largely based on linear instability theory in proton–electron plasmas, which requires comparable growth rates for the EMIC and MM instabilities. Magnetosheath plasmas, however, contain a fraction of heavy ions, and how such composition affects the coexistence of EMIC waves and MMs has been less explored. Using kinetic hybrid simulations with typical magnetosheath parameters, we show that although the presence of heavy ions suppresses the initial linear EMIC instability, EMIC waves arise as MMs develop. The evolving MMs generate flat‐top proton velocity distributions with enhanced resonant populations, which in turn excite EMIC waves. These results extend the conventional coexistence scenario of MMs and EMIC waves and reveal a new pathway for energy transfer among MMs, EMIC waves, and particles in magnetosheath plasmas.

Electromagnetic ion cyclotron (EMIC) and mirror-mode (MM) waves are widely observed in terrestrial and other planetary magnetosheaths. Even though linear theory supports that EMIC and MM waves may grow at comparable rates under suitable plasma conditions, their coexistence is rarely reported within magnetosheaths, primarily due to their similar free energy source from anisotropic plasmas. Using MAVEN spacecraft data, we present the first direct in situ observations of mixed MM and EMIC waves in the Martian magnetosheath. Our observations reveal the concurrent presence of EMIC waves and MM waves, both generated in the Martian magnetosheath. Unlike in the Earth’s magnetosheath, where strong plasma compressions at the quasi-perpendicular bow shock can drive the growth of EMIC or MM waves, our results suggest that, in the Martian magnetosheath, the substantial ion anisotropy to generate EMIC and MM waves is provided by both upstream bow shock compressions and ubiquitous ion pickup processes of newborn ions. This study offers new insights into the role of ion pickup processes in the excitation and growth of EMIC and MM waves within planetary magnetosheaths, particularly in magnetosheaths where both shock heating and newborn ion pickup processes provide the prevailing anisotropic plasma environment, as seen in the magnetosheaths of Venus, Mars, and comets.

Saturn’s magnetosheath provides a natural laboratory for studying the generation and evolution of low-frequency plasma waves that play a key role in regulating temperature anisotropy and mediating wave–particle interactions. Using magnetic field and plasma measurements from the Cassini spacecraft, we investigate the occurrence of mirror mode waves (MMWs) and electromagnetic ion cyclotron (EMIC) waves in relation to the large-scale motion of Saturn’s magnetosheath boundaries, namely, the bow shock and magnetopause. A systematic classification of spacecraft crossings reveals that although MMWs are pervasive across all dynamic conditions, their morphology transitions between peak-like and dip-like structures depending on the direction of boundary motion. EMIC waves occur preferentially during outward motion of the bow shock, particularly on the dawnside, where recent upstream pressure reductions may have driven boundary expansion and formed localized low-beta regions favorable for cyclotron instability. These findings highlight the importance of time-dependent boundary dynamics in shaping the wave environment of planetary magnetosheaths, with broader implications for energy dissipation and plasma stability in rapidly rotating planetary magnetospheres and other astrophysical plasmas with evolving boundaries.

High-precision magnetic field measurements are of great significance for the in-depth study of the physical processes in the astrophysical plasma environment. To obtain accurate natural magnetic fields, in-flight calibration is one key step to obtaining zero offset of the spaceborne fluxgate magnetometer (FGM). Mirror mode structures, widely existing in the solar wind and planetary magnetosheaths and magnetospheres, can be used to calculate the zero offset. However, it is difficult to obtain an accurate zero offset by the current methods using mirror mode structures in the planetary magnetosheath. Here, we develop a new method to calculate the zero offset of the spaceborne FGM using magnetic dips, which are a kind of mirror mode structure. This method is based on the assumption that the magnetic field is zero in the cross section of the magnetic dip. Our method is able to calculate the zero offset using only one magnetic dip. We test this method by using the data from the Magnetospheric Multiscale Mission, and find that the calculation errors of 78.1% of the estimated zero offsets are <0.5 nT when using 25 magnetic dips in the terrestrial magnetosheath. This suggests that our method is able to achieve a high accuracy of the zero offset in the planetary magnetosheath.

Magnetopause position is controlled mainly by the solar wind dynamic pressure and north‐south interplanetary magnetic field component and these quantities are included in different empirical magnetopause models. We have collected about 50,000 of dayside magnetopause crossings observed by THEMIS in course of 2007–2019 and compared the observed magnetopause position with model prediction. The difference between observed and predicted magnetopause radial distance, Robs − Rmod is used for quantifying the model‐observation agreement. Its median values are well predicted for cases up to Robs ≈ 12 RE for all models but higher positive deviations are found for larger magnetopause distances, mainly under a nearly radial field and low dynamic pressure. The analysis reveals their connection with transient magnetopause displacements caused by strong sunward flows in the magnetosheath. We discuss the possible origin of the observed magnetosheath flow switching in terms of the interaction of magnetosheath jets with the magnetopause. Plain Language Summary Comparison of the observed magnetopause crossings with prediction of the magnetopause models reveals that under nearly radial interplanetary magnetic field can be the magnetopause observed several Earth radii farther from the Earth than the models predict. Comprehensive examination of several cases characterized by suitable spacecraft locations leads to the conclusion that the source of such magnetopause displacements is connected with the reformation of nearly parallel bow shock resulting in a strong antisunward jet in the magnetosheath. The jet creates a dip in the magnetopause surface that reverses its direction. The sunward flow in the magnetosheath pulls the magnetopause also sunward. Since these effects are transient in their nature, they cannot be captured by statistical magnetopause models. Key Points The magnetopause is often observed several RE upstream its nominal position under nearly radial IMF Extreme magnetopause displacements are accompanied with strong antisunward magnetosheath jets Reversal of the jet direction is associated with the magnetopause outward displacement

Magnetosheath jets with enhanced dynamic pressure are common in the Earth's magnetosheath. They can impact the magnetopause, causing deformation of the magnetopause. Here we investigate the 3‐D structure of magnetosheath jets using a realistic‐scale, 3‐D global hybrid simulation. The magnetosheath has an overall honeycomb‐like 3‐D structure, where the magnetosheath jets with increased dynamic pressure surround the regions of decreased dynamic pressure resembling honeycomb cells. The magnetosheath jets downstream of the bow shock region with θBn ≲ 20° (where θBn is the angle between the upstream magnetic field and the shock normal) propagate approximately along the normal direction of the magnetopause, while those downstream of the bow shock region with θBn ≳ 20° propagate almost tangential to the magnetopause. Therefore, some magnetosheath jets formed at the quasi‐parallel shock region can propagate to the magnetosheath downstream of the quasi‐perpendicular shock region. Plain Language Summary Magnetosheath jets are high‐speed transient structures frequently observed in the magnetosheath, and they can impact and dent the magnetopause. However, their three‐dimensional (3‐D) structure is still under debt despite decade‐long research. By performing high‐resolution, 3‐D numerical simulation, we reveal that the magnetosheath has an overall honeycomb‐like 3‐D structure where the jets surround regions with lower plasma velocity resembling honeycomb cells. Key Points Magnetosheath jets are studied by a realistic‐scale, 3‐D global hybrid simulation under a radial interplanetary magnetic field (IMF) The magnetosheath has a honeycomb‐like 3D structure where regions of increased dynamic pressure surround those of decreased dynamic pressure The magnetosheath jets formed at the quasi‐parallel shock can propagate to the magnetosheath downstream of the quasi‐perpendicular shock

Coronal mass ejections (CMEs) compress the upstream solar wind as they travel through interplanetary space, forming sheath regions and preceding shocks rich in plasma dynamics. In this study, we identify an abundance of mirror-mode structures within the CME-driven sheath, spanning spatial scales from magnetohydrodynamic to the ion gyroradius. These structures preferentially emerge downstream of quasi-parallel shocks, rather than quasi-perpendicular ones, where elevated ion temperature, anisotropy, and beta provide favorable conditions for their excitation. Unlike planetary magnetosheaths—where mirror modes gradually evolve downstream of bow shocks from wave-like form into nonlinear peak- and hole-like forms—mirror modes in CME-driven sheaths are dominated by magnetic holes, with wave- and peak-like forms rarely present, indicating a rapid instability saturation process. These magnetic holes exhibit larger spatial scales and amplitudes than wave- and peak-like forms and remain stable within the plasma flow, indicating a fully developed state. Multispacecraft observations reveal that they are convected with the sheath plasma flow, suggesting they may constitute the early-stage counterparts of magnetic holes later observed in the solar wind. Our findings highlight the plasma processes triggered by CMEs and help advance understanding of the microphysics of CME-driven disturbances in interplanetary space, including plasma instability excitation, nonlinear evolution, and energy conversion.

Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.

Mirror-mode waves driven by the large temperature anisotropy of T ⊥/T ∣∣ > 1 have been widely observed in the solar wind, planetary magnetosheaths, heliosheath, etc. Recent studies have shown that the phase relations and thermodynamics of the mirror waves observed in the terrestrial magnetosheath may well be interpreted by the linear mixed kinetic–MHD theory of proton mirror instability. In particular, the energy laws possess the form of double-polytropic closures with the thermodynamic exponents being functions of β ⊥,∣∣ = p ⊥,∣∣/(B 2/2μ 0). In this study, we examine the time evolution of proton mirror instability based on the hybrid particle simulations for twenty sets of β ⊥,∣∣ values. Quantitative comparisons between the kinetic simulations, linear Vlasov theory, and observations are made in terms of the growth rates, phase relations, thermodynamic conditions, etc., which show high agreements. In particular, the dependences of various compressibility and thermodynamic exponents on β ⊥,∣∣ are confirmed by the kinetic simulations, which show that the polytropic exponents are in the ranges of γ ⊥ = 0.64 ± 0.21, and γ ∣∣ = 1.07 ± 0.12 consistent with the theoretical predictions and mirror observations of γ ⊥ < 1 and γ ∣∣ ≳ 1. It is shown that the observed features, including the various perturbations and wavelengths, may indeed be reproduced by the nonlinear simulations. The saturated temperature anisotropy β ⊥/β ∣∣ and plasma β ∣∣ show an anticorrelation, which may well be fitted by the modified mirror instability threshold of γ∣∣β∣∣=β⊥2/2+γ⊥β⊥ with γ ⊥ ≈ 0.8, γ ∣∣ ≈ 1.3, and the saturated magnetic field of δ B/B ≈ 0.26 ∼ 0.97 increases with increasing values of β ≈ 1.6 ∼ 8.3.