Like Earth’s space, the Martian space constitutes a collisionless plasma environment. Consequently, the cross-scale energy transfer inherent to the multi-scale nature of collisionless plasmas—a process widespread in Earth’s space—is theoretically expected in Martian space. However, direct evidence for cross-scale energy transfer driven by cross-scale wave-particle interaction—the new model established in Earth’s space—remains elusive in Martian space. Utilizing data from the Mars Atmosphere and Volatile Evolution (MAVEN) and Tianwen-1 spacecrafts, we present the definitive observational evidence for the existence of such process in Martian foreshock region. Fast magnetosonic waves drive enhancements of electron perpendicular energy at their crests through Betatron acceleration, producing a perpendicular temperature anisotropy of the 20–200 eV population to supply the free energy for the excitations of whistler-mode waves. This process constitutes a direct manifestation of energy cascade from ion down to electron scales. Our study discovers a shared process in the terrestrial and Martian space, a finding that can carry broad implications for understanding space environments across planetary systems.

Solar wind measurements by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission provide samples of the heliosphere at 1.38–1.67 AU, and of the upstream conditions that drive numerous processes in the near-Mars plasma environment. We reduce ion measurements from MAVEN’s Solar Wind Ion Analyzer (SWIA), using contextual magnetic field measurements, to 13 independent macroscopic plasma parameters by fitting a convolution of SWIA’s 3-dimensional response function and a superposition of phase-space bi-kappa distribution functions to each measured distribution using an iterative Poisson optimization scheme. This ensemble of parameters represents the solar wind H+ core, H+ beam, and He2+ (alpha) populations, effectively separating each population’s contribution to any measured distribution. Sporadic plasma frequency measurements from MAVEN’s Langmuir Probe and Waves (LPW) instrument are used to calibrate the SWIA measurements such that ion charge densities match LPW-derived electron charge densities. The resulting dataset is effectively ground-truthed, largely corrected for instrumental particularities, and provides a rich timeline of solar wind properties at Mars, including composition, velocities, temperature anisotropies, differential drifts, and degree of thermalization.

The interaction between the supermagnetosonic solar wind and the atmosphere of the weakly magnetized planet Mars forms an induced magnetosphere preceded by a magnetic pileup boundary (MPB) and bow shock (BS). In situ measurements have shown that these boundaries are permanent and well-defined structures that exhibit significant variability driven by external (Sun, solar wind) and internal (planetary) factors. In this work, we used MAVEN observations from 2014 to 2019 to analyze the coupled behavior of the BS and MPB, focusing on their spatial correlation and variability under varying conditions. We examine contiguous BS-MPB spacecraft crossings and the magnetosheath region between them, and we explore the effects of various plasma parameters on the relative position of the boundaries and the thickness of the magnetosheath. We demonstrate a statistical correlation between the BS and MPB positions across multiple timescales, including sustained local solar wind and planetary conditions, seasonal changes, and solar cycle variations. These results support the interpretation that the MPB plays a key role as an electromagnetic obstacle to the solar wind, effectively controlling the formation of the bow shock. We also confirm the limited size of the Martian magnetosheath, both in absolute terms and relative to fundamental plasma scales, which has important implications for understanding the microscopic plasma processes responsible for solar wind thermalization. While acknowledging the limitations of single-spacecraft measurements, this study provides a foundation for future multipoint probing of the Martian environment and the magnetosphere as a system.

With its non-uniform distribution of strong crustal magnetic fields, Mars exhibits complex and highly variable auroral patterns related to both planetary rotation and solar wind conditions. Using in situ electron, ion, and magnetic field data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission, we show that auroral processes associated with these small-scale crustal magnetic fields can be understood in terms of a miniature cycle of magnetic flux and plasma circulations that resemble a miniature version of what occurs at the Earth. However, at Earth this ''Dungey cycle", named after its discoverer, operates in the presence of a global intrinsic dipole field with a strength ~100 times stronger and spatial scales ~20 times larger. From a universal perspective, the current finding adds a new entry to the ''zoo" of auroral concepts that enriches our understanding of the diversity of (exo)planetary plasma our understanding of how planets interact with their space environments.

At planets that possess strong dipole magnetic fields, the Zwan-Wolf effect acts to squeeze plasma along magnetic flux tubes, aiding in the deflection of the solar wind flow about the planet. While the effect has been most studied at Earth, candidate observations have also been made at the outer planets. Here we present observations of the Zwan-Wolf effect occurring at Mars, an unmagnetized planet that lacks a dipole magnetic field. Our analysis of observations made by NASA's Mars Atmosphere and Volatile EvolutioN spacecraft suggest that while the Zwan-Wolf effect is likely continuously active within the Martian ionosphere, it operates below detection thresholds of typical plasma analyzers most of the time. However, an interplanetary coronal mass ejection impact at Mars in December 2023 greatly enhanced the Zwan-Wolf effect within the ionosphere, allowing it to be observed, and highlighting the importance of space weather events for these unmagnetized planetary systems.

The induced magnetosphere of Mars is highly dynamic, driven by both the upstream solar wind and the planet’s crustal magnetic fields. This variability can occur on timescales much shorter than a single spacecraft orbit, making it difficult to distinguish between spatial and temporal variations in the induced magnetosphere. In this study, we utilize simultaneous multipoint observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1 missions to investigate how the induced magnetosphere responds to dynamic changes in the solar wind. We report a magnetic reconnection event observed by MAVEN in the Martian magnetotail, occurring a few minutes after an interplanetary magnetic field (IMF) rotation observed by Tianwen-1 in the upstream solar wind. This reconnection event is characterized by clear Hall magnetic field signatures and high-speed ion jets, indicating the presence of a diffusion region. Our analysis of the change in the magnetic field morphology suggests that this reconnection was likely triggered by this IMF rotation, occurring during the resulting reconfiguration of the induced magnetosphere. This multipoint study demonstrates the important role of dynamic upstream solar wind conditions, particularly IMF rotations, in driving the plasma processes in the Martian magnetotail, contributing to our understanding of solar wind energy and momentum transfer and their roles in ion escape in Mars’s hybrid magnetosphere.

Direct electric field measurements during certain ionosphere-magnetosheath transitions on the dayside of Mars reveal a presence of localized (<20 km thickness along vertical direction) strong (>40 mV/m) electric field located at the solar wind stagnation point. This electric field is nearly collocated with the ion composition boundary where ionospheric oxygen ions are observed to be accelerated up to similar to 1 keV, forming a layer of higher temperature plasma around the stagnation point. Simulations demonstrate that the observed localized electric field enhancement can create this hotter plasma layer population on either side of the boundary. This plasma layer can have an impact on the solar wind coupling with the planet and forms a reservoir for heavy ion escape.

Various types of auroral emissions have been observed at (partially) magnetized planets (e.g., Earth, Jupiter, and Mars). Auroral emissions have also been observed at Venus, an unmagnetized planet, by the Pioneer Venus Orbiter (PVO) and ground‐based telescopes. By applying a linear relation, this study predicts the possible CO Cameron‐band emission brightness at Venus using electron observations from Venus Express (VEx). Our results suggest that to produce the PVO observations, electron acceleration is not required as in the case of discrete aurorae at magnetized planets; rather, the magnetic access of precipitating electrons to the lower atmosphere is the more limiting factor for auroral occurrence. This study helps better understand how aurorae can occur at an unmagnetized planet, in contrast to magnetized planets. It also has implications for future Venus mission design: auroral imaging can serve as a remote sensing tool to characterize the magnetization state of the Venus nightside atmosphere.

Abstract Mars's magnetotail represents a unique case within the solar system, embodying both intrinsic and induced magnetic fields. Yet, the electron dynamics within this region have remained largely unexplored. Utilizing nine years of electron and magnetic field data from the Mars Atmosphere and Volatile EvolutioN mission (MAVEN), we conducted a comprehensive statistical analysis to uncover the average electron characteristics in the Martian induced magnetotail for the first time. Our findings revealed a distinct pattern of electron behavior: in the lobe regions, electrons tend to converge toward the current sheet, driven by an ambipolar electric field that is directed from the current sheet toward the lobe. Additionally, we observed that electrons are more energetic in the +E hemisphere, where the solar wind electric field points away from Mars, compared to the opposite hemisphere. This mirrors the behavior of planetary ions and supports the hypothesized formation mechanism of sinuous auroras.

Understanding the nature of planetary bow shocks is beneficial for advancing our knowledge of solar wind interactions with planets and fundamental plasma physics processes. Here, we utilize data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to investigate the Martian bow shock, revealing its distinctive characteristics within our solar system. We find that unlike other planetary shocks, the reformation of Mars's bow shock driven by the ultra-low frequency (ULF) waves is more global and less dependent on shock geometries. This distinct behavior is attributed to the broad distribution of ULF waves in the upstream region at Mars, generated not only by shock-reflected ions but also by planetary protons. Additionally, during the reformation process, the amplitude of the ULF waves and the steepened structures are significantly large. This results in the newly reformed shock exceeding the original one, a phenomenon not observed at other planets under similar shock conditions. Therefore, the ULF waves significantly enhance the complexity of shock dynamics and play a more substantial role at Mars compared to other planets.

In the magnetosheath of planets, mirror modes triggered by the mirror mode instability form as large magnetic structures imprisoning dense and hot plasma in their midst. The free energy created from a large pressure anisotropy at their origin can come from several sources. At Earth and other planets, the quasi-perpendicular shock provides the plasma with the necessary heating along the perpendicular direction to the local magnetic field. At Mars, the extended exosphere theoretically provides another source of temperature anisotropy, with exospheric neutrals locally ionised and subsequently picked up by local electric fields creating unstable ring-beam velocity distribution functions. Using the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission plasma instrumentation, we show for the first time at Mars the unmistakable signature of near locally-generated mirror mode structures due to pickup protons. The pickup ion mechanism is reminiscent of temperature anisotropy-generating mechanisms found at comets, the outgassing moons of Jupiter, and in other heliospheric scenarios.

In order to study spatial distributions of global magnetosheath structures, physicists often rely upon spatial binning, whereby space is divided into cells, each filled with the average value of all spacecraft measurements within that cell. The traditional binning schema utilizes a fixed Cartesian grid of cube bins. The morphology of the magnetosheath's boundaries are not fixed, however, but driven by upstream and planetary conditions. Therefore, the spatial structures are not fixed in Cartesian space, and thus a Cartesian binning technique will produce a highly coarse grained spatial distribution. We propose an alternative binning technique utilizing a scale normalized dimensionless coordinate system defined in terms of magnetosheath morphology. To demonstrate the efficacy of this technique, we apply a basic implementation to the Martian system. We are thereby able to achieve a high-resolution spatial mapping of bow shock and magnetosheath processes and resolve spatial structures that are washed out when binned traditionally. In particular, we can resolve the shock overshoot, analyze the dominant forces acting at the shock, and obtain fine-scale distributions of the bulk ion plasma magnetosheath forces and thermalization mechanisms. Magnetic tension and magnetic pressure gradient are compared. The ion pressure divergence at the shock is found to significantly vary in line with the solar wind temperature anisotropy. The dependency of the mirror mode instability on location and Mach number, and its implications for thermalization processes in the small Martian magnetosheath are investigated.

The Martian bow shock has been extensively studied through magnetic field and plasma instrument observations from various Mars space missions. However, prior investigations primarily involve statistical analyses based on single spacecraft crossings, leaving the asymmetry of the Martian bow shock unstudied through simultaneous two-spacecraft observations. In this study, utilizing simultaneous observations from Tianwen-1 and MAVEN, we examine the instantaneous asymmetry of the Martian bow shock. We present the asymmetry of the Martian bow shock in the Mars-Solar-Electric and Mars-Solar-Orbital reference frames, possibly influenced by the solar wind motional electric field and Martian crustal magnetic field, respectively. Moreover, we suggest that the bow shock exhibits increased asymmetry under stronger solar wind motional electric field conditions. This study highlights how a two-point observation approach offers valuable insights into the dynamic behavior of the Martian induced magnetosphere. Scientists have been studying the Martian bow shock, which slows down the solar wind from supersonic to subsonic, using instruments on different Mars missions. But most studies only use data from one spacecraft, so we don't know much about how the bow shock varies in different places at the same time. In this study, we looked at data from two spacecraft, Tianwen-1 and MAVEN, at the same time to see if we could find any differences. We found that the bow shock is different in the northern and southern parts of Mars in different reference frames, and this might be because of the solar wind electric field and the Martian crustal field. We also noticed that the bow shock is more different when the solar wind electric field is stronger. Such two-spacecraft observations helps us understand more about how the magnetic environment around Mars works. We investigated the asymmetry of Martian bow shock utilizing two-spacecraft observations at distinct locations The dayside Martian crustal field may induce the north-south asymmetry of the bow shock The solar wind electric field may cause bow shock asymmetry in the Mars-Solar-Electric frame, with stronger fields increasing the effect

Venus, lacking an intrinsic global dipole magnetic field, serves as a textbook example of an induced magnetosphere, formed by interplanetary magnetic fields (IMF) enveloping the planet. Yet, various aspects of its magnetospheric dynamics and planetary ion outflows are complex and not well understood. Here we analyze plasma and magnetic field data acquired during the fourth Venus flyby of the Parker Solar Probe (PSP) mission and show evidence for closed topology in the nightside and downstream portion of the Venus magnetosphere (i.e., the magnetotail). The formation of the closed topology involves magnetic reconnection-a process rarely observed at non-magnetized planets. In addition, our study provides an evidence linking the cold Venusian ion flow in the magnetotail directly to magnetic connectivity to the ionosphere, akin to observations at Mars. These findings not only help the understanding of the complex ion flow patterns at Venus but also suggest that magnetic topology is one piece of key information for resolving ion escape mechanisms and thus the atmospheric evolution across various planetary environments and exoplanets.

It has been long observed at Mars that electron fluxes are enhanced during the tail current sheet crossings, of which the cause is not well understood. We use a novel approach to reveal one of the electron energization mechanisms with observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. We find the field-aligned potential, derived from comparing electron distribution functions, to be approximately linearly correlated with the logarithmic values of the local total ion density. This is the expected behavior of an ambipolar electrostatic potential. The large amplitude of potential (tens to hundreds of V) is a result of both a significant density gradient (1 order of magnitude) and the high electron temperature (tens of eV) in the tail. Such a mechanism is not limited to ion density enhancements at current sheet crossings but can be present anywhere that large ion density gradients and hot electrons are present.

On 26-27 December 2022, Mars experienced an extremely low-density solar wind stream, which was encountered first by Earth because of the radial alignment of the two planets (i.e., Mars opposition). During this event, two important properties of the ionospheric and magnetospheric states changed significantly in response to the low solar wind ram pressure, as inferred from the superthermal electron observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. The interface between the ionosphere and magnetosphere expanded to thousands of kilometers, outside of the nominal bow shock locations, coinciding with the expansion of the cold planetary ions. Meanwhile, the ambipolar electrostatic potential arising from the ionospheric electron pressure gradient increased from the nominal similar to -0.7 to similar to -2 V (relative to the lower ionosphere). This enhanced ambipolar potential likely facilitated the observed ionosphere expansion. This study characterizes Mars's magnetospheric and ionospheric response to the disappearing solar wind event in December 2022 During the event, open and closed field lines extend beyond the nominal bow shock location, just as the planetary cold ions The ionospheric ambipolar potential drop is enhanced from the nominal similar to -0.7 to similar to -2 V, likely facilitating the ionosphere expansion

We present a case study of plasma and magnetic field observations in the Martian magnetotail using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission during an orbit when the spacecraft was in the optical shadow, past the dusk terminator and downstream of the strongest crustal magnetic fields. In this region, we observed multiple magnetic field rotations (a signature of currents) closely associated with energized (up to 100 eV) electron populations. Several transitions between closed and draped magnetic topologies also occur in this region, which are likely to be caused by magnetic reconnection between the interplanetary magnetic field (IMF) and crustal magnetic fields. We also observe two regions of energized, counter-streaming electrons, which are rare in the magnetotail, but twice as likely to occur downstream of strong crustal magnetic fields when they are near the evening terminator. Together, the multiple magnetic field rotations, topological changes, and counter streaming electrons suggest the presence of an electric potential structure similar to those observed above the auroral arc regions at Earth.

A snow growth model for rimed snowfall (SGMR) was developed based on the growth processes of vapor deposition, aggregation, and riming. The SGMR is initialized by radar reflectivity (Z) at the cloud top and thereafter simulates the vertical evolution of size spectra. The SGMR is based on the zeroth- and second-moment conservation equations with respect to mass, and thus conserves the number concentration and Z, respectively. New mass- and area-dimension expressions suitable for synoptic clouds are utilized in the model, and therefore the assumption of specific ice particle shapes is not required. In addition, the new approach to parameterizing riming has the advantage of a smooth and gradual growth of mass and area by riming. In general, the processes of vapor deposition and aggregation lead to larger ice particles that fall faster and therefore, produce a larger snowfall rate (rs). The rs and ice water content with the inclusion of riming are significantly greater than that produced by the vapor deposition and aggregation alone. Moreover, rs is sensitive to the cloud drop size distribution. The size spectra predicted by the SGMR were compared with those from two cases of Lagrangian spiral descent through frontal and cirrus clouds, and good agreement is seen between the vertical profiles of SGMR and observations. This analytical SGMR, due to its accuracy and short running time, can be used in climate models and remote sensing.

Charles Bowers, James Slavin, Gina DiBraccio, Gang Kai Poh, Shaosui Xu, David Brain, Jared Espley, and David Mitchell Department of Climatology and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA (@umich.edu) NASA Goddard Space Flight Center, Greenbelt, MD, USA (@nasa.gov) University of California, Berkeley, CA, USA (@berkeley.edu) Laboratory of Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA (@colorado.edu