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Aims. We study the instantaneous asymmetry of the Martian bow shock during a change in the direction of the interplanetary magnetic field (IMF) and for steady-state conditions. Specifically, we study the asymmetry with regard to the convective electric field and to the crustal fields of Mars.

Methods. Two methods were used: First, a single-spacecraft method in which a switch in hemisphere in the Mars solar-electric (MSE) coordinate system was studied during a change in the direction of the interplanetary magnetic field. Second, we used a dual-spacecraft method wherein near simultaneous bow shock crossings on opposite hemispheres were studied. The dual bow shock crossings were then compared to a bow shock model, and the difference in the distance to the model was used as a measure of asymmetry.

Results. With the single-spacecraft method, an asymmetry with respect to the solar wind convective electric field, Esw, was found, wherein the bow shock was farther from the planet in the ZMSE <0 hemisphere, that is, the - E hemisphere. With the dual-spacecraft method, the mean of the magnitude of the asymmetries in the individual case was 0.13 RM. However, the standard deviation was as high as the mean, and no significant asymmetry could be attributed either to the solar wind convective electric field or to the Martian crustal fields. A strong asymmetry without a clear correlation to these factors was found nonetheless. Possible causes of the measured asymmetry are discussed.

Conclusions. The magnitude of the asymmetries in individual observations is larger than the average asymmetries. This indicates that the shape of the Martian bow shock is dynamic and influenced by fluctuations or wave phenomena.

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.

Context. Dynamic pressure enhancements, known as magnetosheath jets, are plasma structures with a higher dynamic pressure than the surrounding plasma. They have been thoroughly studied at Earth and recently discovered around other planetary bodies. However, studies on jets outside of the terrestrial magnetosheath have only been performed as case studies.

Aims. We present the first statistical study of jets in the Martian plasma environment. Methods. Our database was assembled using ten years of Mars Atmosphere and Volatile Evolution (MAVEN) mission data sampling various regions in the Martian plasma environment.

Results. Our database contains 82 645 jets, which have an average dynamic pressure increase of a factor of 2.34. The majority of jets are observed close to the bow shock in the magnetosheath. Most jets are driven by a combination of velocity and density enhancement, although the distribution is skewed toward density enhancement, as compared to jets at Earth. The jets are often colder than their background. The median scale size of Martian jets is 0.67 R_M.

Conclusions. Jets in the Martian plasma environment are similar to jets observed in the terrestrial magnetosheath, however, there are some differences. In Martian jets, the density enhancement dominates over the velocity; whereas in terrestrial jets, the velocity enhancement dominates over the density enhancement. Furthermore, jets are more deflected compared to the surrounding magnetosheath plasma. Martian jets are likely to be smaller than terrestrial jets, but they are larger relative to the scale size of the magnetosphere.

Context: The solar wind affects the plasma environment around all Solar System bodies. A strong solar wind dynamic pressure pushes plasma boundaries closer to these objects. For small objects, kinetic effects on scales smaller than an ion gyroradius play an important role and species with various mass-per-charge may act differently. In this case, the solar wind composition can be important.

Aims: Protons are the dominant ion species in the solar wind, however, the density of alpha particles can sometimes increase significantly. We analyse the effect of different solar wind alpha-to-proton ratios on the plasma boundaries of a weakly outgassing comet (Q ≈ 1 − 2 × 1026 s−1). In addition, we investigate the energy transfer between the solar wind ions, the cometary ions, and the electromagnetic fields.

Methods: Using the hybrid model Amitis, we simulated two different alpha-to-proton ratios and analysed the resulting plasma structures. We calculated the power density (E ∙ J) of all three ion species (solar wind protons, alphas, and cometary ions) to identify load and generator regions. The integrated 1D power density shows the evolution of the power density from the upstream solar wind to downstream of the nucleus.

Results: A higher alpha-to-proton ratio leads to a larger comet magnetosphere, but weaker magnetic field pile-up. The protons transfer energy to the fields and the cometary ions in the entire upstream region and the pile-up layer. Upstream of the nucleus, alphas are inefficient in transferring energy and can act as a load, especially for low alpha-to-proton ratios. The transfer of energy from alphas to cometary ions happens further downstream due to their larger inertia.

Conclusions: For a multi-species solar wind, the mass loading and energy transfer upstream of the pile-up layer will be most efficient for the species with the lowest inertia. Protons represent such a species, and different gyroradii of the ions result in distinct flow patterns for each individual species.

In the plasma environment of a comet, waves are generated on vastly different temporal and spatial scales. Wave observations were carried out during the cometary flybys in the 1980s and 1990s as well as by the Rosetta spacecraft which accompanied comet 67P/Churyumov-Gerasimenko between 2014 and 2016. Waves are thought to contribute to the transfer of energy in the ionised coma. One of the fundamental plasma waves observed in space is the Langmuir wave, which appears at or above the electron plasma frequency. The Mutual Impedance Probe of the Rosetta Plasma Consortium (RPC-MIP) recorded frequency spectra of electric field fluctuations in the cometary plasma, and we used these spectra in order to detect and identify Langmuir waves. Langmuir waves were found during the part of the Rosetta mission when the comet was less than 2.65-2.8 AU from the Sun. The Langmuir waves appear near, but always outside, the diamagnetic cavity boundary, in a region where, at much lower frequencies, steepened magnetosonic waves also are present.

Magnetosheath jets, transient plasma structures of enhanced dynamic pressure, have been observed to trigger ultra-low frequency (ULF) waves in the magnetosphere. These ULF waves contribute to energy transport in the magnetosphere-ionosphere system. Therefore, there is a need to estimate the energy input into the ionosphere due to jet-triggered ULF waves. In this study, we combine measurements from Magnetospheric Multiscale, ground-based magnetometers, the EISCAT radar on Svalbard, and SuperDARN to estimate the Joule heating in the ionosphere resulting from jet impacts at the magnetopause. Focusing on three jets observed on 2016-01-07 we were able to calculate the Joule heating for two jets. We found an average Joule heating rate of (Formula presented.) mW/m2 which is on par with other processes such as field line resonances. However, due to the short duration and spatial confinement of the jet-induced ULF waves, the average energy input was only (Formula presented.) J. This suggests that the energy deposition of jet-triggered ULF waves is small compared to other magnetospheric processes, and thus does not significantly impact the average energy budget of the magnetosphere.

Magnetosheath jets, plasma structures with enhanced dynamic pressure, are frequently observed in the terrestrial magnetosheath. However, their mass, momentum, and energy content are still unknown. We utilize Amitis, a 3D hybrid-kinetic plasma simulation, to study the mass, momentum, and energy content of jets in the subsolar magnetosheath. We also analyze the kinetic, thermal, and electromagnetic energy flux associated with jets. Jets comprise up to 21% of the quasi-parallel magnetosheath and can carry up to half of the kinetic energy. Furthermore, jets convert kinetic energy to thermal energy. Our hybrid simulations also suggest that while jets can form downstream of the quasi-perpendicular shock, their volume and energy content are much small compared to jets downstream of the quasi-parallel bow shock. We conclude that magnetosheath jets play a vital role in heating up the magnetosheath and significantly influence the dynamics of the quasi-parallel magnetosheath.

In the Earth's magnetosphere wave-particle interaction is a major ion energization process, playing an important role for the atmospheric escape. A common type of ion heating is associated with low-frequency broadband electric wave fields. For such waves the energy is not concentrated to a certain narrow frequency range and exhibits no peaks or dips in a power spectrum. If there are enough fluctuations close to the ion gyrofrequency the electric field may still come in resonance with gyrating ions and heat them perpendicular to the background magnetic field. We perform a proof-of-concept study to investigate if this heating mechanism may contibute significantly to the energization of planetary ions also in the induced magnetosphere of Venus. We assume Alfvénic fluctuations and estimate the electric field spectral density based on magnetic field observations. We find typical estimated electric spectral densities of a few (Formula presented.) /Hz close to Venus. This corresponds to a heating rate of a few eV/s. We consider an available interaction time of (Formula presented.) 300 s and conclude that this mechanism could increase the energy of an oxygen ion by about a keV. Observed thermal energies are in the range 100–1,000 eV and thus, resonant wave heating may also be important at Venus.

At a low activity comet the plasma is distributed in an asymmetric way. The hybrid simulation code Amitis is used to look at the spatial evolution of ion velocity distribution functions (VDFs), from the upstream solar wind (SW) to within the comet magnetosphere where the SW is heavily mass-loaded by the cometary plasma. We find that the spatial structures of the ions and fields form a highly asymmetric induced magnetosphere. The VDFs of SW and cometary ions vary drastically for different locations in the comet magnetosphere. The shape of the VDFs differ for different species. The SW protons show high anisotropies that occasionally resemble partial rings, in particular at small cometocentric distances. A second, decoupled, proton population is also found. Solar wind alpha particles show similar anisotropies, although less pronounced and at different spatial scales. The VDFs of cometary ions are mostly determined by the structure of the electric field. We perform supplementary dynamic particle backtracing to understand the flow patterns of SW ions that lead to these anisotropic distributions. This tracing is needed to understand the origin of cometary ions in a given part of the comet magnetosphere. The particle tracing also aids in interpreting observed VDFs and relating them to spatial features in the electric and magnetic fields of the comet environment.