Umeå University's logo

Aims: We aim to quantify the width of the quasi-perpendicular Martian bow shock region to deepen the understanding of why the width is variable and which factors affect it, and to explore the implications on thermalization.

Methods: To quantify the width, 2074 quasi-perpendicular bow shock crossings from a database were studied. Upstream conditions, such as Mach numbers, dynamic pressure, ion densities, and other factors, were considered. Furthermore, the difference between the downstream and upstream temperature was measured.

Results: We found that the shock region width is correlated with the magnetosonic Mach number, the critical ratio, and the overshoot amplitude. The region was found to be anticorrelated with dynamic pressure. The width is not affected by the upstream ion density of the investigated species or by the upstream temperature. The difference between the downstream and upstream temperature is not affected by the shock region width.

Conclusions: We found that the factors that affect the stand-off distance of the bow shock, such as the magnetosonic Mach number and dynamic pressure, also affect the width. The width is also positively correlated with the overshoot amplitude, indicating that the structures are coupled or that they are affected by largely the same conditions. The lack of a correlation with the ion temperature difference indicates that the shock region width does not affect the ion thermalization.

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.

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.

Mars, lacking an intrinsic dynamo, is an ideal laboratory to comparatively study induced magnetospheres, which can be found in other terrestrial bodies as well as comets. Additionally, Mars is of particular interest to further exploration due to its loss of habitability by atmospheric escape and possible future human exploration. In this context, we propose the Mars Magnetospheric Multipoint Measurement Mission (M⁵), a multi-spacecraft mission to study the dynamics and energy transport of the Martian induced magnetosphere comprehensively. Particular focus is dedicated to the largely unexplored magnetotail region, where signatures of magnetic reconnection have been found. Furthermore, a reliable knowledge of the upstream solar wind conditions is needed to study the dynamics of the Martian magnetosphere, especially the different dayside boundary regions but also for energy transport phenomena like the current system and plasma waves. This will aid the study of atmospheric escape processes of planets with induced magnetospheres. In order to resolve the three-dimensional structures varying both in time and space, multi-point measurements are required. Thus, M⁵ is a five spacecraft mission, with one solar wind monitor orbiting Mars in a circular orbit at 5 Martian radii, and four smaller spacecraft in a tetrahedral configuration orbiting Mars in an elliptical orbit, spanning the far magnetotail up to 6 Mars radii with a periapsis just outside the Martian magnetosphere of 1.8 Mars radii. We not only present a detailed assessment of the scientific need for such a mission but also show the resulting mission and spacecraft design taking into account all aspects of the mission requirements and constraints such as mass, power, and link budgets. Additionally, different aspects of the mission programmatics like a possible mission timeline, cost estimates, or public outreach are shown. The common requirements for acceptance for an ESA mission are considered. The mission outlined in this paper was developed during the Alpbach Summer School 2022 on the topic of “Comparative Plasma Physics in the Universe”.