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We examine the newly discovered phenomena of sinuous aurora on the nightside of Mars, using images of 130.4 and 135.6 nm oxygen emission measured by the Emirates Mars Mission EMUS ultraviolet spectrograph, and upstream measurements from the MAVEN and Mars Express spacecraft. They are detected in ∼3% of observations, totaling 73 clear detections. These emissions are narrow, elongated (1,000–6,000 km), cross Mars' UV terminator, and are oriented generally toward the anti‐solar point, clustering into north, south, east, and west‐oriented groups. Diverse morphologies are observed, though some spatial features, such as broad curves, may in some cases be due to temporal aliasing of aurora motion as each image is built up over 15–20 min. Sinuous aurora form away from Mars' strongest crustal magnetic fields and can be interrupted by moderate crustal fields. Sinuous aurora occurrence increases strongly with solar wind pressure, though brightness shows only a weak positive dependence on pressure. Interplanetary magnetic field (IMF) clock angle affects their occurrence and orientation: sinuous aurora show a broad range of orientations centered on the solar wind convection electric field (Econv) direction and forming in the +Econvhemisphere, although with moderate clockwise and counterclockwise average “twists” for westward and eastward IMF, respectively. From these features we infer a link between sinuous aurora and electron energization in Mars' magnetotail current sheet, where field geometry on the +Econvside of the sheet is more organized and symmetric. Determination of specific triggering conditions for sinuous aurora requires further investigation. Sinuous aurora are narrow, extended patterns of UV emission caused by long, thin channels of energized electrons striking Mars' nightside upper atmosphere. We study images of these aurora taken by the Emirates Mars Mission EMUS instrument. 73 cases of sinuous auroras were found (∼3% occurrence rate) with lengths ranging from 1,000 to 6,000 km. These auroras usually cross Mars' day‐night boundary and extend in the direction opposite to the Sun. They tend to cluster into groups oriented toward the north, south, east, and west directions with a diverse array of shapes. Sinuous aurora generally form away from Mars' strongest crustal magnetic fields. They occur more frequently for higher solar wind pressure. Their orientations are affected by the interplanetary magnetic field (IMF), displaying a broad range of orientations centered on the direction of the electric field in the solar wind, and forming in the hemisphere to which this electric field points, although with moderate counterclockwise and clockwise average “twists” for eastward and westward IMF, respectively. From these features we infer a link between sinuous aurora and a sheet of current in Mars magnetic tail, wherein the aurora‐causing electrons may be energized before falling into the upper atmosphere to produce aurora. These narrow emission features form away from strong crustal fields, oriented anti‐sunward, cross the terminator, are detected in 3% observationsOccurrence increases with solar wind pressure, certain interplanetary magnetic field orientations, and in the positive motional electric field hemisphereSinuous aurora may be related to magnetotail asymmetry and electron energization processes occurring in the tail current sheet These narrow emission features form away from strong crustal fields, oriented anti‐sunward, cross the terminator, are detected in 3% observations Occurrence increases with solar wind pressure, certain interplanetary magnetic field orientations, and in the positive motional electric field hemisphere Sinuous aurora may be related to magnetotail asymmetry and electron energization processes occurring in the tail current sheet

We present the first observations of the dayside coronal oxygen emission in far ultraviolet (FUV) measured by the Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM). The high sensitivity of EMUS is providing an opportunity to observe the tenuous oxygen corona in FUV, which is otherwise difficult to observe. Oxygen resonance fluorescence emission at 130.4 nm provides a measurement of the upper atmospheric and exospheric oxygen. More than 500 oxygen corona profiles are constructed using the long–exposure time cross–exospheric mode (OS4) of EMUS observations. These profiles range from ∼200 km altitude up to several Mars radii (>6 RM) across all seasons and for two Mars years. Our analysis shows that OI 130.4 nm is highly correlated with solar irradiance (solar photoionizing and 130.4 nm illuminating irradiances) as well as changes in the Sun–Mars distance. The prominent short term periodicity in oxygen corona brightness is consistent with the solar rotation period (quasi–27–day). A comparison between the perihelion seasons of Mars Year (MY) 36 and MY 37 shows interannual variability with enhanced emission intensities during MY 37, due to the rise of Solar Cycle 25. These observations show a highly variable oxygen corona, which has significant implications on constraining the photochemical escape of atomic oxygen from Mars. The highly sensitive Emirates Mars Ultraviolet Spectrometer (EMUS) onboard Emirates Mars Mission (EMM) is capable of observing ultraviolet emissions emanating from Mars. Oxygen in the Martian exosphere is hard to see because it's tenuous. In this study, the analysis of long exposure time EMUS optical observations show that the hot oxygen corona on Mars has a short term variability due to solar rotation. Hot oxygen corona also shows a long–term variability that depends on the Sun–Mars distance and the solar cycle progression. When comparing data from two Martian years, it is noticed that the oxygen corona became brighter when the Sun is more active. Brighter O corona is observed during perihelion and dimmer during aphelion, indicating a strong relationship with the Sun‐Mars distanceThe variation in OI 130.4 nm brightness shows a linear correlation with solar EUV irradiance, with a short‐term solar rotation periodicityInterannual variability is observed from MY 36 to MY 37, showing an enhancement in O corona brightness with the rise of Solar Cycle 25 Brighter O corona is observed during perihelion and dimmer during aphelion, indicating a strong relationship with the Sun‐Mars distance The variation in OI 130.4 nm brightness shows a linear correlation with solar EUV irradiance, with a short‐term solar rotation periodicity Interannual variability is observed from MY 36 to MY 37, showing an enhancement in O corona brightness with the rise of Solar Cycle 25

The localized crustal magnetic fields of Mars play an important role in the planet’s ionosphere‐solar wind interaction. Various physical processes in the induced magnetosphere, such as particle precipitation, field‐aligned currents, and ion outflow, are usually associated with the crustal magnetic cusp regions, where field lines are mostly vertical and open to space. Due to the small spatial scale (a few hundred km) of the Martian crustal magnetic cusps, localized models with high spatial resolutions and ion kinetics are needed to understand the physical processes. We adapt the simulation platform HYB developed at the Finnish Meteorological Institute to a moderately strong magnetic cusp above the Martian exobase with a 2‐D simulation domain assuming periodic boundary conditions on the third dimension. Two plasma sources are included in the simulation: hot protons from the induced magnetosphere and cold heavy ions (O+) from the ionosphere. Our model results can qualitatively reproduce the vertical electric potential drop, particle transport, and field aligned current in the cusp region. The vertical electric potential is built up mostly by the Hall electric field as a result of the separation between ion and electron fluxes of the downward plasma flow. By varying the model inputs, we found that the vertical potential drop depends on ionospheric ion density and magnetic field strength. These results tell us that energy is transferred from magnetospheric plasma to ionospheric plasma through the vertical electric potential buildup in magnetic cusps and how this process may affect electron precipitation, ion escape, and ionosphere conditions at Mars. A hybrid model qualitatively reproduced the vertical potential drop and field aligned currents in Martian crustal magnetic cusp regionsThe vertical electric potential drop is mostly from the Hall electric field as a result of energy input from the downward plasma flowThe vertical electric potential drop decreases with ionospheric ion density and increases with magnetic field strength A hybrid model qualitatively reproduced the vertical potential drop and field aligned currents in Martian crustal magnetic cusp regions The vertical electric potential drop is mostly from the Hall electric field as a result of energy input from the downward plasma flow The vertical electric potential drop decreases with ionospheric ion density and increases with magnetic field strength

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 ∼ −0.7 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 2022During the event, open and closed field lines extend beyond the nominal bow shock location, just as the planetary cold ionsThe ionospheric ambipolar potential drop is enhanced from the nominal ∼ −0.7 to ∼ −2 V, likely facilitating the 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 ∼ −0.7 to ∼ −2 V, likely facilitating the ionosphere expansion

The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. The current paper studies electron temperatures in the dayside for two regions where (1) crustal magnetic fields are dominant and (2) draped magnetic fields are dominant. Overall, the electron temperature is lower in the crustal‐field regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet conditions, which is associated with the local extreme ultraviolet energy deposition. The current models underestimate the electron temperature above 250‐km altitude in the crustal‐field region. Electron heat conduction associated with a photoelectron transport in the crustal‐field regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron's upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustal‐field region should be considered for future numerical simulations. At high altitudes, the electron temperature is lower for the crustal‐field region than for the IMF‐dominated draped regionsThe low temperatures for the crustal‐field region are due to a heat transport along the field lines between lower and upper atmosphereKinetic effects such the magnetic mirror and the ambipolar electric field may affect the heat transport along crustal magnetic field lines

Magnetic topology is important for understanding the Martian plasma environment, including particle precipitation, energy transport, cold ion escape, and wave‐particle interaction. In this study, we combine two independent but complementary methods in order to determine magnetic topology based on superthermal electron energy and pitch angle distributions. This approach removes ambiguities that result from using either energy or pitch angle alone, providing a more accurate and comprehensive determination of magnetic topology than previous studies. By applying this combined technique, we are able to identify seven magnetic topologies, including four types of closed field lines, two types of open field lines, and draped. All seven topologies are present in the Mars environment and are mapped in longitude, latitude, solar zenith angle, and altitude with the combined technique near the terminator. We find that closed field lines with double‐sided loss cones are frequently present over stronger crustal field regions at higher altitudes. We also show that the cross‐terminator closed field lines are more spatially confined over strong crustal regions, likely connecting nearby magnetic crustal patches. In contrast, cross‐terminator closed loops over weak crustal regions have more distantly separated foot points, most likely connecting distant crustal patches. A technique combining e‐ pitch angle and energy distribution is developed to most accurately infer up to seven magnetic topologies at MarsClosed magnetic loops with trapped electrons occur frequently over stronger crustal field regions at higher altitudesCross‐terminator closed loops are more spatially confined over strong crustal regions and distantly separated over weak crustal regions

We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in low‐altitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E> 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E< 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E< 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E< 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At ∼175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E> 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kilo‐electron‐volt ions suggest a selection effect in radial magnetic fields for lower‐energy Marsward ions, compared to reflection of higher‐energy anti‐Sunward ions. Precipitating kilo‐electron‐volt ions show energy deposition rates of 3.6 ×10−6W/m2and sputtering escape rates from precipitating O+ions of 1.5 ×105/(cm2.s) and 2.1 ×106/(cm2.s) are calculated. Mars Atmosphere and Volatile EvolutioN arrived at Mars on 21 September 2014 to study the effects of the solar wind interaction on the upper atmosphere. This study reports the raining of both energetic electrons and multiple populations of ions at low altitudes and over regions of ancient magnetic field from the Martian crust. These observations are associated with large magnetic field deflections and large electric field fluctuations. The results are important for understanding plasma transport and associated electrodynamics where the crustal magnetic fields point vertically toward or away from the planet. Such analysis was not possible with previous missions, which did not include the complete set of space plasma instruments carried by Mars Atmosphere and Volatile EvolutioN. Some ions display behaviors not expected for the small curvature of the crustal magnetic fields; ions that are locally tied that would require much larger magnetic field structures or ions injected along the direction of the magnetic field. Oxygen ions that originate from Mars that have been picked up by the solar wind and moving at very high speeds are selected over regions of vertical magnetic field to travel directly toward the planet. These ions will have head on impacts with Mars to heat and blast atmosphere out into space. Investigated plasma transport and associated electrodynamics during ion energy flux spikes in radial crustal fields on the Mars daysidePrecipitating ion and electron energy flux spikes on closed field consisting of ion beams E> 1.4 keV and broad ion distributions E< 1.4 keVConsidered impact of low‐altitude precipitating O+ions E> 25 eV on localized heating and atmospheric escape

Without an upstream monitor at Mars to provide a contemporaneous measurement of solar wind conditions, it is useful to have techniques of inferring the upstream solar wind conditions using downstream data. We develop a method to estimate the upstream interplanetary magnetic field (IMF) clock angle, defined as the orientation of the IMF vector in the plane perpendicular to the solar wind velocity, at Mars using magnetometer data from the Mars Atmosphere and Volatile Evolution (MAVEN) mission. The technique fits MAVEN magnetometer data from within the Martian magnetosheath to a model of the draped magnetic field direction in a coordinate system aligned with the motional electric field. The results provide a proxy for the clock angle that agrees with upstream measurements and reproduces the observed distribution of clock angles. Even if upstream observations are available for a given orbit, the proxy provides an estimate of the clock angle at the time when the spacecraft is in the magnetosheath, which may correct for inherent temporal variability, because the solar wind varies on timescales shorter than the 4.5‐hr MAVEN orbit. The clock angle proxy can be applied for any orientation of the MAVEN orbit, even when MAVEN does not traverse into the upstream solar wind. A proxy for the upstream IMF clock angle is derived from Martian magnetosheath magnetic fieldsThe distribution of inferred clock angles reproduces the measured distributionThe uncertainty of the proxy reflects IMF fluctuations with time

We present the effects of the local magnetic field configurations on ions precipitating into the upper atmosphere of Mars using Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Precipitating pickup planetary heavy ions (O+, O2+, and CO2+) are of particular interest in the Martian plasma environment because they potentially enhance the sputtering loss of ambient neutral particles. In addition, solar wind protons (and H+pickup ions) penetrate into the dayside atmosphere due to the direct interaction with the Martian obstacle. We present a statistical study showing that precipitating ion fluxes are typically enhanced by a factor of 2–3 under radial field configurations. We also show that the crustal fields have a shielding effect; the precipitating fluxes are significantly reduced by ∼50% under the strong crustal fields ( ≳100 nT), where the local magnetic field is oriented with a more horizontal component to the surface. These trends are seen consistently regardless of ion species, as well as the observed locations including dayside/nightside, subsolar longitudes, and ±Ehemispheres in the Mars‐centered solar electric (MSE) coordinates. In particular, the local magnetic field configurations control precipitating ions with energies lower than a few keV, while precipitating high‐energy ion fluxes are likely independent of the local magnetic field configurations. Precipitating ion fluxes are known to vary by at least an order of magnitude depending on the upstream solar wind. Therefore, the local magnetic field configurations turn out to be the secondary factor in modulating precipitating ion fluxes at Mars. We investigated the effects of the local crustal field configurations on precipitating ion fluxes into MarsPrecipitating ion fluxes increase by a factor of 2–3 with the radial crustal fields while decrease by half with horizontal crustal fieldsThe local crustal fields consistently control precipitating ion fluxes regardless of their species and the observed location

The Martian magnetosphere is a product of the interaction of Mars with the interplanetary magnetic field and the supersonic solar wind. The location of the bow shock has been previously modeled as conic sections using data from spacecraft such as Phobos 2, Mars Global Surveyor, and Mars Express. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft arrived in orbit about Mars in November 2014 resulting in thousands of crossings to date. We identify over 1,000 bow shock crossings. We model the bow shock as a three‐dimensional surface accommodating asymmetry caused by crustal magnetic fields. By separating MAVEN's bow shock encounters based on solar condition, we also investigate the variability of the surface. We find that the shock surface varies in shape and location in response to changes in the solar radiation, the solar wind Mach number, dynamic pressure of the solar wind, and the relative local time location of the strong crustal magnetic fields (i.e., whether they are on the dayside or on the nightside). A shock wave forms when the supersonic solar wind flows around objects in the Solar System. We studied the shape of this bow shock at Mars; the obstacle to the solar wind at Mars is the upper atmosphere and the patches of the crust that have localized strong magnetic fields. Previous studies have shown that the Martian bow shock can change due to changing solar wind or the location of crustal magnetic fields. Two‐dimensional equations have been used to create mathematical models of the Martian bow shock, but they have implicit assumptions about the symmetry of the surface. Using over 2 years of observations from Mars Atmosphere and Volatile Evolution Mission, we have used a general surface equation to model the Martian bow shock fully in three‐dimensions, which is able to represent the asymmetric shape of the surface. We find that while changes in the solar wind change the size of the Martian bow shock, the location of the crustal fields are most important factor in producing the asymmetric shape of the shock. Investigating how the bow shock varies under different solar wind conditions can be important toward understanding of how the Sun impacts the Martian magnetosphere that can drive important processes, such as atmospheric. Using MAVEN observations, we present a model of the Martian bow shock that unlike previous conic models is fully three‐dimensionalThe bow shock is asymmetric, occurring further from the planet in the Southern Hemisphere where the strongest crustal magnetic fields areThe bow shock is variable; its location and shape are influenced by solar radiation, solar wind, and location of crustal fields

The precipitation of suprathermal electrons is the dominant external source of energy deposition and ionization in the Martian nightside upper atmosphere and ionosphere. We investigate the spatial patterns and variability of ionizing electrons from 115 to 600 km altitude on the Martian nightside, using CO2electron impact ionization frequency (EIIF) as our metric, examining more than 3 years of data collected in situ by the Mars Atmosphere and Volatile EvolutioN spacecraft. We characterize the behavior of EIIF with respect to altitude, solar zenith angle, solar wind pressure, and the geometry and strength of crustal magnetic fields. EIIF has a complex and correlated dependence on these factors, but we find that it generally increases with altitude and solar wind pressure, decreases with crustal magnetic field strength and does not depend detectably on solar zenith angle past 115°. The dependence is governed by (a) energy degradation and backscatter by collisions with atmospheric neutrals below ~220 km and (b) magnetic field topology that permits or retards electron access to certain regions. This field topology is dynamic and varies with solar wind conditions, allowing greater electron access at higher altitudes where crustal fields are weaker and also for higher solar wind pressures, which result in stronger draped magnetic fields that push closed crustal magnetic field loops to lower altitudes. This multidimensional electron flux behavior can in the future be parameterized in an empirical model for use as input to global simulations of the nightside upper atmosphere, which currently do not account for this important source of energy. We investigate the patterns and variability of electron impact ionization frequency (EIIF) below 600 km on the Martian nightsideEIIF generally increases with altitude and solar wind pressure and decreases with crustal magnetic field strengthPatterns of EIIF reflect the combined solar wind‐dependent topology of Mars' variable draped IMF and planet‐fixed crustal magnetic fields

Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single‐fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low‐altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment. Various Martian plasma models show clear morphological differences in the state of the global plasmaComparing these models with MAVEN data shows what physics is necessary to model different physical regionsModeled escape rates compare well with each other and with estimates from data, despite morphological differences in escaping ion flux maps

Magnetic field lines at Mars act as direct pathways for both energy inflow and ion escape. Local variations in magnetic field topology can therefore directly impact the interaction between the solar wind and the Martian ionosphere. One method of analyzing magnetic topology is through the use of electron pitch angle distributions (PADs). Previous PAD investigations have characterized magnetic topology in the Martian system using data from the Mars Global Surveyor spacecraft, but these studies were orbitally constrained to ∼400 km altitude and 2 a.m./2 p.m. local time. With the Mars Atmosphere and Volatile Evolution (MAVEN) mission, we are now able to extend this analysis to a larger range of altitudes and local times. Here we use electron PADs measured using the Solar Wind Electrostatic Analyzer and Magnetometer instruments on MAVEN to analyze the magnetic topology of the nightside Martian environment. We use several characteristic PAD shapes to determine where Martian magnetic field lines are open or closed to the solar wind and present frequency maps of how these PAD shapes vary both geographically and with altitude. Finally, we present an initial analysis of the variation of the PAD shapes with local time, finding that trapped electron distributions become increasingly frequent as crustal fields rotate from dusk to dawn across the nightside of Mars. Electron pitch angle distributions are used to determine magnetic topology at MarsElectron voids and trapped distributions indicate closed topology, found more frequently near crustal sources and at lower altitudesTrapped distributions become more frequent in crustal fields as they move from dusk to dawn across the nightside

Direct interaction between the solar wind (SW) and the Martian upper atmosphere forms a characteristic region, called the induced magnetosphere between the magnetosheath and the ionosphere. Since the SW deceleration due to increasing mass loading by heavy ions plays an important role in the induced magnetosphere formation, the ion composition is also expected to change around the induced magnetosphere boundary (IMB). Here we report on relations of the IMB, the ion composition boundary (ICB), and the pressure balance boundary based on a statistical analysis of about 8 months of simultaneous ion, electron, and magnetic field observations by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We chose the period when MAVEN observed the SW directly near its apoapsis to investigate their dependence on SW parameters. Results show that IMBs almost coincide with ICBs on the dayside and locations of all three boundaries are affected by the SW dynamic pressure. A remarkable feature is that all boundaries tend to locate at higher altitudes in the southern hemisphere than in the northern hemisphere on the nightside. This clear geographical asymmetry is permanently seen regardless of locations of the strong crustal Bfields in the southern hemisphere, while the boundary locations become higher when the crustal Bfields locate on the dayside. On the nightside, IMBs usually locate at higher altitude than ICBs. However, ICBs are likely to be located above IMBs in the nightside, southern, and downward ESWhemisphere when the strong crustal Bfields locate on the dayside. Locations of boundaries (the IMB, the ICB, and the β∗) at Mars show a north‐south asymmetry mainly on the nightsideIMBs coincide with ICBs on the dayside, and all boundaries depend on the SW dynamic pressure and the southern crustal BfieldsIMBs and ICBs tend to be located at high altitudes in the nightside, southern, and downward ESWhemisphere

Daily averaged heavy ion escape rates from HALFSHEL hybrid simulations of the solar wind interaction with the Martian ionosphere are compared to the ion escape rates reported by Brain et al. (2015). The simulation rates are found to be in agreement with the rates measured by Mars Atmosphere and Volatile EvolutioN (MAVEN). When the simulation rates are adjusted for known variability in the Martian system, the ion escape rates are within 40% of the MAVEN results. The ion escape rate is found to vary linearly with the solar wind speed. Using the simulation results to scale the MAVEN ion escape rate to include ions of all kinetic energies, we predict a total heavy ion escape rate of 1.2 × 1025ions/s. The assumptions used to derive the total ion escape by Brain et al. (2015) are tested against the simulation results and are found to be excellent. Ion escape rates from the simulations are in agreement with MAVENThe assumptions used to scale the MAVEN ion fluxes to account for unsampled regions are validScaling the MAVEN ion escape rates to account for ions of all kinetic energies gives a total heavy ion escape rate of 1.2 × 1024ions/s

We present results from a global Mars time‐dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3‐D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics‐based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross‐section areas in the terminator plane for both of the boundaries. The model‐predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars‐centered Solar Orbital itself may account for ∼60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape‐fostering effect by positively affecting the transterminator ion flow cross‐section area. The inhomogeneous crustal magnetic field at Mars has important controlling effects on the Mars‐solar wind interaction and has both shielding and escape‐fostering effects on atmospheric erosion. The Mars crustal field has a clear, significant influence on both the IMB and the BSThe global crustal field distribution collectively affects IMB and BS locationsThe crustal field has both shielding and escape‐fostering effects for atmospheric loss

The Martian magnetotail is a complex regime through which atmospheric particles are lost to space. Our current understanding of Mars' tail continues to develop with the comprehensive particle and field data collected by Mars Atmosphere and Volatile EvolutioN (MAVEN). In this work, we identify periods when MAVEN encounters multiple current sheet crossings through a single tail traversal in order to understand tail dynamics. We apply an analysis technique that has been developed and validated by using multipoint measurements in order to separate the spatial and temporal properties associated with current sheet flapping. Events are classified into periods of steady flapping, due to a global motion of the current sheet, and kink‐like flapping, resulting from localized wave propagation along the tail current sheet. Out of 106 periods during which multiple current sheet crossings were observed, 20 were due to steady flapping and 10 from kink‐like flapping. A majority of the kink‐like events resulted from waves propagating in the opposite direction of the solar wind convection electric field, regardless of their location in the tail, unlike at Earth and Venus. This finding suggests that possible magnetosphere energy sources, whereby plasma is accelerated and removed from the Martian environment, are not located in the central magnetotail; rather, these waves may be driven by a source located at the tail flank based on the direction of the solar wind electric field. Therefore, by identifying potential sources of impulsive energy release in the tail, we may better understand mechanisms that drive atmospheric loss at Mars. MAVEN data analysis of tail current sheet dynamics at Mars reveals that steady global flapping occurs more often than kink‐like local flappingA majority of the kink‐like flapping events are generated by waves propagating in the opposite direction from the solar wind electric fieldMars' tail exhibits similar flapping to Earth and Venus with different wave propagation directions suggesting different energy sources

The Mars Atmosphere and Volatile Evolution mission has obtained comprehensive particle and magnetic field measurements. The Solar Wind Electron Analyzer provides electron energy‐pitch angle distributions along the spacecraft trajectory that can be used to infer magnetic topology. This study presents pitch angle‐resolved electron energy shape parameters that can distinguish photoelectrons from solar wind electrons, which we use to deduce the Martian magnetic topology and connectivity to the dayside ionosphere. Magnetic topology in the Mars environment is mapped in three dimensions for the first time. At low altitudes (<400 km) in sunlight, the northern hemisphere is found to be dominated by closed field lines (both ends intersecting the collisional atmosphere), with more day‐night connections through cross‐terminator closed field lines than in the south. Although draped field lines with ~100 km amplitude vertical fluctuations that intersect the electron exobase (~160–220 km) in two locations could appear to be closed at the spacecraft, a more likely explanation is provided by crustal magnetic fields, which naturally have the required geometry. Around 30% of the time, we observe open field lines from 200 to 400 km, which implies three distinct topological layers over the northern hemisphere: closed field lines below 200 km, open field lines with foot points at lower latitudes that pass over the northern hemisphere from 200 to 400 km, and draped interplanetary magnetic field above 400 km. This study also identifies open field lines with one end attached to the dayside ionosphere and the other end connected with the solar wind, providing a path for ion outflow. Pitch angle‐resolved electron energy shape parameters are used to deduce magnetic topologyClosed magnetic field lines dominate low altitudes (<400 km) of the northern hemisphere on the daysideThe 3‐D view of the Martian magnetic topology is presented for the first time

The Mars Atmosphere and Volatile Evolution (MAVEN) observations show that the global spatial distribution of ions precipitating toward the Martian upper atmosphere has a highly asymmetric pattern relative to the upstream solar wind electric field. MAVEN observations indicate that precipitating planetary heavy ion fluxes measured in the downward solar wind electric field (−E) hemisphere are generally larger than those measured in the upward electric field (+E) hemisphere, as expected from modeling. The −E(+E) hemispheres are defined by the direction of solar wind electric field pointing toward (or away from) the planet. On the other hand, such an asymmetric precipitating pattern relative to the solar wind electric field is less clear around the terminator. Strong precipitating fluxes are sometimes found even in the +Efield hemisphere under either strong upstream solar wind dynamic pressure or strong interplanetary magnetic field periods. The results imply that those intense precipitating ion fluxes are observed when the gyroradii of pickup ions are estimated to be relatively small compared with the planetary scale. Therefore, the upstream solar wind parameters are important factors in controlling the global spatial pattern and flux of ions precipitating into the Martian upper atmosphere. MAVEN shows that the precipitating heavy ion fluxes are stronger in the −Ehemisphere rather than in the +EhemisphereStrong precipitating ion fluxes are detected even in the +Ehemisphere during the disturbed solar wind periodsGyroradii of pickup ions play an important role in controlling the precipitating ion patterns in MSE coordinates

We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of a giant magnetic flux rope in the Martian dayside ionosphere. The flux rope was observed at an altitude of <300 km, downstream from strong subsolar crustal magnetic fields. The peak field amplitude was ∼200 nT, resulting in the largest difference between the observed magnetic field strength and a model for crustal magnetic fields of the entire MAVEN primary science phase. MAVEN detected planetary ions, including H+, O+, and O2+, across the structure. The axial orientation estimated for the flux rope indicates that it likely formed as a result of interactions between the local crustal and overlaid draped interplanetary magnetic fields. Pitch angle distributions of ionospheric photoelectrons imply that this structure is connected to the Martian upper atmosphere. However, the flux rope is not present in observations at the next commensurable orbit crossing (approximately two Martian days later), implying that it eventually detaches from the atmosphere and is carried downstream. The flux rope observations occurred during an interplanetary coronal mass ejection event at Mars, suggesting that the disturbed upstream state played a role in allowing the interplanetary magnetic field to penetrate deeper into the Martian ionosphere than is typical, allowing the formation of the flux rope. MAVEN observed a giant flux rope near the subsolar point of the Martian ionosphere, downstream from the strong crustal fieldsThe observed giant ionospheric flux rope was formed via interactions between the local crustal and overlaid draped magnetic fieldsThe event was observed during the ICME passage by Mars, indicating that the ICME played a role in forming the observed giant flux rope

The interaction between Mars and the solar wind results in different plasma regimes separated by several boundaries, among which the separation between the sheath flow and the ionosphere is complicated. Previous studies have provided different and sometimes opposite findings regarding this region. In this study, we utilize observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission to revisit boundaries within this region and perhaps reconcile some differences. More specifically, we start with the photoelectron boundary (PEB), a topological boundary that separates magnetic field lines having access to the dayside ionosphere (open or closed) from those connected to the solar wind on both ends (draped). We find that large gradients in the planetary ion densiti occur across the PEB and that the dominant ion switches from heavy planetary ions to protons near the PEB, indicating that the PEB falls within the ion composition boundary (ICB). Furthermore, our results show that the PEB is not a pressure balance boundary; rather the magnetic pressure dominates both sides of the PEB. Meanwhile, we find that the PEB is located where the shocked solar wind flow stops penetrating deeper into the ionosphere. These findings suggest the PEB marks the top of the Mars dayside ionosphere and also the interface where the sheath plasma flow deflects around the obstacle going downstream. Large gradients in planetary ion density occur across the photoelectron boundary (PEB) and the PEB falls within the ion composition boundaryThe PEB can be considered as the top of the Mars dayside ionosphereThe PEB is not a pressure balance boundary but is located where the shocked sheath flow is diverted around the ionosphere Large gradients in planetary ion density occur across the photoelectron boundary (PEB) and the PEB falls within the ion composition boundary The PEB can be considered as the top of the Mars dayside ionosphere The PEB is not a pressure balance boundary but is located where the shocked sheath flow is diverted around the ionosphere

Although photochemistry‐enabled escape of oxygen is a dominant atmospheric loss process at Mars today, ion outflow plays an essential role in the long‐term evolution of Mars' atmosphere. Apart from heavy planetary ions such as O+, O2+, and CO2+, the loss of planetary protons is also important because it could be related to water loss. To study planetary proton loss due to solar wind interaction, we improve the 4‐species (O+, O2+, CO2+, and H+) single‐fluid magnetohydrodynamic (MHD) model of Mars, to a 5‐species (separating planetary protons and solar wind protons) MHD model so that the two types of protons can be tracked separately. The global distributions of solar wind protons and planetary ions at low altitudes are investigated. The calculated planetary proton escape rates are larger than heavy ion loss rates and solar wind proton inflows for both solar maximum and minimum conditions. Planetary proton escape rates are 1–2 orders less than neutral hydrogen loss, suggesting that planetary protons could contribute to no >10% of the hydrogen loss under current conditions. By comparing normal cases with cases for which H‐O charge exchange reactions or electron impact ionizations are switched off, we find that H‐O charge exchange mainly affects densities at low altitudes, while impact ionizations exert great influence on escape rates at high altitudes. The overall results suggest the specific treatment of proton origins in models of Mars atmosphere escape provides better insight into the contributing processes, and should be included in future studies focusing on water's fate. It is commonly believed that Mars has lost most of its atmosphere. While there are many works on the escape rates of heavy ions such as O+, O2+, and CO2+, there are few studying proton loss which is also important due to its relation to the loss of water. We separate the protons from the solar wind and protons originating in the planetary atmosphere, so that the 4‐species (O+, O2+, CO2+, and H+) single‐fluid magnetohydrodynamic (MHD) model is improved to a 5‐species (separating planetary protons and solar wind protons) MHD model. The global distributions of solar wind protons and planetary ions at low altitudes are discussed. The calculated escape rates suggest that planetary proton loss is important compared with heavy ion loss and solar wind proton inflow, even though planetary proton loss is no >10% of previously estimated atomic hydrogen loss. We investigate the effects of two types of reactions where protons are involved: H‐O charge exchange and electron impact ionization. We find that impact ionization is important at high altitudes therefore also important for escape rates, while H‐O charge exchange mainly exerts influence at low altitudes. The total integrations of chemical reactions indicate their relative importance. Solar wind protons and planetary protons are analyzed separately using the updated magnetohydrodynamic modelPlanetary proton loss is estimated to be larger than heavy ion loss, but 1–2 orders less than neutral hydrogen lossThe effects of impact ionization and H‐O charge exchange reactions are quantified Solar wind protons and planetary protons are analyzed separately using the updated magnetohydrodynamic model Planetary proton loss is estimated to be larger than heavy ion loss, but 1–2 orders less than neutral hydrogen loss The effects of impact ionization and H‐O charge exchange reactions are quantified

In order to better represent Mars-solar wind interaction, we present an unprecedented model achieving spatial resolution down to 50 km, a so far unexplored resolution for global kinetic models of the Martian ionized environment. Such resolution approaches the ionospheric plasma scale height. In practice, the model is derived from a first version described in Modolo et al. (2005). An important effort of parallelization has been conducted and is presented here. A better description of the ionosphere was also implemented including ionospheric chemistry, electrical conductivities, and a drag force modeling the ion-neutral collisions in the ionosphere. This new version of the code, named LatHyS (Latmos Hybrid Simulation), is here used to characterize the impact of various spatial resolutions on simulation results. In addition, and following a global model challenge effort, we present the results of simulation run for three cases which allow addressing the effect of the suprathermal corona and of the solar EUV activity on the magnetospheric plasma boundaries and on the global escape. Simulation results showed that global patterns are relatively similar for the different spatial resolution runs, but finest grid runs provide a better representation of the ionosphere and display more details of the planetary plasma dynamic. Simulation results suggest that a significant fraction of escaping O+ions is originated from below 1200 km altitude. A new 3-D parallelized multispecies hybrid code for Mars-SW interactionA parametric study to determine the influence of the spatial resolution on the simulation resultsInvestigation of the importance of the extended exosphere on Mars's plasma escape

The penetration boundary of shocked solar wind (magnetosheath) into the Martian upper atmosphere is typically located at altitudes above 800 km. However, magnetosheath plasma occasionally penetrates into low altitudes below 400 km. Here we used Mars Global Surveyor magnetic field and electron observations from April 1999 to November 2006 to investigate the magnetosheath penetration events. We identified 1145 events and found that both solar wind dynamic pressure (Pdyn) and the orientation of the interplanetary magnetic field (IMF) control the occurrence of the events. The magnetosheath penetration events during low Pdynperiods tend to be distributed in low latitudes of the northern hemisphere or where the crustal magnetic field is weak, while the event locations are widely distributed in terms of the latitude under high Pdynconditions. During low Pdynperiods, a remarkable feature is that the observational probability is approximately 2.4 times larger during periods of the “away” IMF sector than during the “toward” sector. The northern hemisphere during the away sector corresponds to the upward electric field hemisphere due to the convection of draping solar wind origin magnetic flux tubes. These results thus indicate that the magnetosheath penetrations into Martian upper atmosphere more often occur in the upward electric field hemisphere than the downward hemisphere during low Pdynperiods. Large‐amplitude undulation excited by the Kelvin‐Helmholtz instability in the upward electric field hemisphere is a candidate process to cause the asymmetric penetration during low Pdynperiods. Another possibility might be the mirror‐mode instability by the asymmetric distribution of planetary pickup ions. Magnetosheath often penetrates into Martian ionosphere under away IMF periodMagnetosheath often penetrates into Martian ionosphere in northern hemisphereThe magnetosheath penetrations mainly occur in upward electric field hemisphere

Discrete aurorae have been observed at Mars by multiple spacecraft, including Mars Express, Mars Atmosphere and Volatile EvolutioN (MAVEN), and most recently the United Arab Emirates Hope spacecraft. Meanwhile, there have been studies on the source particles responsible for producing these detectable aurorae (termed “auroral electrons”). By utilizing empirical criteria to select auroral electrons established by Xu et al. (2022, https://doi.org/10.1029/2022GL097757), we conduct statistical analyses of the impact of upstream drivers on the occurrence rate and fluxes of auroral electrons. We find the occurrence rate increases with upstream dynamic pressure and weakly depends on the interplanetary magnetic field strength. Meanwhile, the integrated auroral electron flux somewhat decreases with increasing upstream drivers. Auroral electron precipitation also occurs more frequently and is more intense over regions of strong crustal fields compared to weak crustal fields. Aside from emissions, auroral electrons are expected to cause significant impact ionization and enhance the plasma density locally. In this study, we also quantify the nightside ionospheric impact of auroral electron precipitation, specifically the thermal ion (O+, O2+${O}_{2}^{+}$, and CO2+$C{O}_{2}^{+}$) density enhancement, with MAVEN observations. Our results show that the ion density is increased by up to an order of magnitude at low altitudes. The crustal effects on ion density profiles for nominal electron and auroral electron precipitation are also discussed. Localized auroral emissions have been observed at Mars by multiple spacecraft, including Mars Express, Mars Atmosphere and Volatile EvolutioN (MAVEN), and most recently the United Arab Emirates Hope spacecraft. Meanwhile, there have been studies on the source particles responsible for producing these detectable aurorae, termed “auroral electrons.” By utilizing previously established criteria to select auroral electrons, we conduct statistical analyses of the impact of upstream drivers on the occurrence rate and also the intensity of auroral electrons. In the meantime, auroral emission is not the sole effect of electrons impacting the collisional atmosphere, but also an enhanced local ionization. Using both MAVEN observations, we show that the ion density is increased by up to an order of magnitude at low altitudes comparing auroral electron and nonauroral electron events. The occurrence rates of auroral electrons increase but their integrated energy fluxes somewhat decrease with increasing upstream driversWe quantify the planetary ion density enhancement resulting from auroral electron precipitation to be up to an order of magnitudeAuroral electron precipitation occurs more frequently and is more intense over strong crustal fields than weak crustal fields The occurrence rates of auroral electrons increase but their integrated energy fluxes somewhat decrease with increasing upstream drivers We quantify the planetary ion density enhancement resulting from auroral electron precipitation to be up to an order of magnitude Auroral electron precipitation occurs more frequently and is more intense over strong crustal fields than weak crustal fields

We investigated the formation mechanism of a molecular ion plume and its contribution to ion escape based on Mars Atmosphere and Volatile EvolutioN (MAVEN) observations from November 2014 to October 2019 and numerical models. Here, we report a CO2+‐rich plume event and a statistical study of the molecular ion plume. MAVEN observed a CO2+‐rich plume event, in which the maximum CO2+escape flux is approximately 4.2 × 106cm−2s−1, on 28 August 2015 under strong solar wind dynamic pressure conditions. A numerical simulation using strong solar wind dynamic pressure conditions from the event suggested that the molecular ion plume is formed by deep penetration of the solar wind‐induced electric field, which is caused by strong solar wind dynamic pressure. A statistical study showed that CO2+plume events tend to be observed under high solar wind dynamic pressure and strong electric field conditions. This tendency is consistent with the formation mechanism of the molecular ion plume suggested by the event study. The O2+plume does not show the same tendency. This is because O2+ions are abundant in the high‐altitude ionosphere, and O2+plumes can be formed even under weak solar wind conditions. The subsolar crustal magnetic fields tend to prevent the formation of the molecular ion plume by shielding the ionosphere from the solar wind. The escape rate ratio O+:O2+:CO2+$\left({\mathrm{O}}^{+}:{\mathrm{O}}_{2}^{+}:{\text{CO}}_{2}^{+}\right)$is approximately 45:53:3 during the whole statistical survey period, suggesting that a molecular ion plume from the ionosphere is a non negligible ion escape channel from Mars. It has been considered that Mars had a thick atmosphere to sustain liquid water on the surface approximately 4 billion years ago, while the Martian atmosphere is thin at the present time. Ion escape to space is one of the candidates that contributes to atmospheric loss. Both atomic oxygen ions (O+) and molecular ions, such as O2+and CO2+, can contribute to ion escape from Mars. However, the escape mechanism and contribution of molecular ions are far from understood. Based on observations by the Mars Atmosphere and Volatile EvolutioN mission, we investigate energetic ion escape channels from Mars, which are accelerated by electric fields. The results show that the strong pressure of the solar wind facilitates energetic molecular ion escape, while crustal magnetization on the Martian surface prevents it. The escape rate ratio O+:O2+:CO2+$\left({\mathrm{O}}^{+}:{\mathrm{O}}_{2}^{+}:{\text{CO}}_{2}^{+}\right)$is approximately 45:53:3, suggesting the importance of energetic molecular ion escape from Mars. When observed, polar plume flux of O2+${\mathrm{O}}_{2}^{+}$(CO2+${\text{CO}}_{2}^{+}$) is 4 (2) times higher than O+, but they are 4 (23) times less frequently observed than O+The CO2+${\text{CO}}_{2}^{+}$plume becomes detectable only under high solar wind dynamic pressure conditions, while the O2+${\mathrm{O}}_{2}^{+}$plume is detected more frequentlySubsolar crustal magnetic fields tend to prevent the formation of molecular ion plumes, especially under low dynamic pressure conditions When observed, polar plume flux of O2+${\mathrm{O}}_{2}^{+}$(CO2+${\text{CO}}_{2}^{+}$) is 4 (2) times higher than O+, but they are 4 (23) times less frequently observed than O+ The CO2+${\text{CO}}_{2}^{+}$plume becomes detectable only under high solar wind dynamic pressure conditions, while the O2+${\mathrm{O}}_{2}^{+}$plume is detected more frequently Subsolar crustal magnetic fields tend to prevent the formation of molecular ion plumes, especially under low dynamic pressure conditions

Electron precipitation is usually the dominant source of energy input to the nightside Martian atmosphere, with consequences for ionospheric densities, chemistry, electrodynamics, communications, and navigation. We examine downward‐traveling superthermal electron flux on the Martian nightside from May 1999 to November 2006 at 400 km altitude and 2 A.M. local time. Electron precipitation is geographically organized by crustal magnetic field strength and elevation angle, with higher fluxes occurring in regions of weak and/or primarily vertical crustal fields, while stronger and more horizontal fields retard electron access to the atmosphere. We investigate how these crustal field‐organized precipitation patterns vary with proxies for solar wind (SW) pressure and interplanetary magnetic field (IMF) direction. Generally, higher precipitating fluxes accompany higher SW pressures. Specifically, we identify four characteristic spectral behaviors: (1) “stable” regions where fluxes increase mildly with SW pressure, (2) “high‐flux” regions where accelerated (peaked) spectra are more common and where fluxes below ~500 eV are largely independent of SW pressure, (3) permanent plasma voids, and (4) intermittent plasma voids where fluxes depend strongly on SW pressure. The locations, sizes, shapes, and absence/existence of these plasma voids vary significantly with solar wind pressure proxy and moderately with IMF proxy direction; average precipitating fluxes are 40% lower in strong crustal field regions and 15% lower globally for approximately southwest proxy directions compared with approximately northeast directions. This variation of the strength and geographic pattern of the shielding effect of Mars' crustal fields exemplifies the complex interaction between those fields and the solar wind. Mars' crustal fields control electron precipitation patterns on the nightsideThese patterns are affected by the solar wind pressure and IMF directionElectron fluxes in “intermittent plasma voids” vary by 3–4 orders of magnitude

We analyzed Mars Atmosphere and Volatile Evolution (MAVEN) and Venus Express (VEX) data of magnetic flux ropes observed in both Mars and Venus nightside induced magnetosphere, in order to understand their statistical characteristics and possible formation processes. We statistically identified 382 (286) events at Mars (Venus) via the minimum variance analysis and investigated the flux rope properties including their geometrical configurations of axial core field direction and spatial distributions. Interestingly, there is no significant difference with respect to the variety of the flux rope axial orientation between Mars and Venus, indicating that about at least one fourth of events do not necessitate magnetotail reconnection for their formations. However, the spatial distribution shows that flux ropes at Venus tend to be observed near the central plasma sheet, whereas those at Mars are more spread out. Moreover, the events tend to be observed more frequently in the −Ehemisphere, where the solar wind electric field (ESW) is pointing toward the planet, rather than in +Ehemisphere, where the ESWdirection is away from the planet. The geographical distribution shows that flux ropes at Mars tend to be observed more frequently in the southern hemisphere where the strong crustal magnetic fields are primarily distributed. Therefore, such a tendency indicates that the Martian crustal magnetic fields could play significant roles on generating flux ropes in the nightside magnetosphere of Mars. We statistically investigated how to create flux ropes in the nightside magnetosphere of Mars and VenusWe found the similar variety of the flux ropes axial orientation between Mars and VenusFlux ropes in Mars magnetotail concentrate above the strong crustal magnetic field region We statistically investigated how to create flux ropes in the nightside magnetosphere of Mars and Venus We found the similar variety of the flux ropes axial orientation between Mars and Venus Flux ropes in Mars magnetotail concentrate above the strong crustal magnetic field region

The motion of charged particles is governed by electromagnetic forces at high altitudes at Mars and thus the characterization of electrostatic potential and electric fields is important for understanding ion escape at Mars. In this study, we utilize measurements from the Mars Atmosphere and Volatile EvolutioN mission to derive electrostatic potentials above the collisional atmosphere at Mars. We find averaged potentials to be up to ∼100 V in the magnetosheath and down to ∼−70 V in the tail, with respect to the upstream. We then derive electric fields based on averaged potential maps, ranging ∼0.01−0.1$\sim 0.01-0.1$V/km. These data‐derived electric fields are in good agreement with ambipolar electric fields from a multi‐fluid magnetohydrodynamic (MHD) model. MHD results also reveal that these large electric fields mainly originate from the electron pressure gradient in the magnetosheath and in the transition region from the hot solar wind flow to the cold ionospheric flow. This work provides the first data‐based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere). The motion of charged particles is governed by electric and magnetic force at high altitudes at Mars and thus the characterization of electric fields is important for understanding ion escape, a form of atmospheric escape, at Mars. In this study, we utilize measurements from the Mars Atmosphere and Volatile EvolutioN mission to derive electric fields at high altitudes, which occur at density and/or temperature gradients in a collisionless plasma to maintain charge neutrality with highly mobile electrons and much slower moving ions. These data‐derived electric fields are in good agreement with electric fields from a magnetohydrodynamic model. Model results also reveal the plasma source of these electric fields. Our characterization of these electric fields provides a better understanding of the interaction between Mars and the Sun and, to a large extent, Mars' atmospheric escape. This work provides the first data‐based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere)We find averaged ambipolar potentials ranging from ∼−70 to +100 V and ambipolar electric fields of ∼0.01−0.1$\sim 0.01-0.1$V/kmMHD results show a good agreement with data‐derived electric fields and also suggest the plasma source of these ambipolar electric fields This work provides the first data‐based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere) We find averaged ambipolar potentials ranging from ∼−70 to +100 V and ambipolar electric fields of ∼0.01−0.1$\sim 0.01-0.1$V/km MHD results show a good agreement with data‐derived electric fields and also suggest the plasma source of these ambipolar electric fields

Martian crustal magnetic fields influence the solar wind interaction with Mars in a way that is not fully understood. In some locations, crustal magnetic fields act as “mini‐magnetospheres,” shielding the planet's atmosphere, while in other locations they act as channels for enhanced energy input and particle escape. The net effect of this system is not intuitively clear, but previous modeling studies have suggested that crustal fields likely decrease global ion escape from Mars. In this study, we use data from the Mars Atmosphere and Volatile EvolutioN spacecraft to analyze how crustal magnetic fields influence both global and local ion escape at Mars. We find that crustal fields only increase ion escape if ions are not bound tightly to the magnetic field. Specifically, ion escape is increased only if closed magnetic fields trap 35% or less of energized oxygen ions. In any other case, crustal fields decrease both global and local ion escape by as much as 40% and 80%, respectively. This suggests that the presence of crustal magnetic fields has had a moderate impact on atmospheric ion loss throughout Martian history, potentially influencing the planet's atmospheric evolution and habitability. The loss of the Martian atmosphere over time has transformed Mars from a potentially warm and wet planet to the cold, dry world we observe today. This atmospheric loss is often suggested to be the result of Mars losing its global magnetic field 3 billion years ago. However, the loss of a global dynamo did not leave the Martian system devoid of planetary magnetic fields. Rather, the crust of Mars still contains scattered pockets of magnetic field that extend outward into the planet's atmosphere. In some areas, these magnetic fields shield the planetary atmosphere much in the same way as the Earth's magnetic field, while in other areas the magnetic fields channel energy down into the planet's atmosphere, potentially driving enhanced atmospheric loss. In this study, we use spacecraft data from Mars Atmosphere and Volatile EvolutioN to analyze the extent to which Martian crustal magnetic fields affect atmospheric escape at Mars. We show that the shielding provided by crustal magnetic fields reduces present‐day ion escape by as much as 40%, and suggest that over time this may have been an important factor in the total amount of atmosphere lost from the planet. We present a new method for estimating the influence of Martian crustal magnetic fields on ion escapeMartian crustal magnetic fields affect global ion escape by at most 40%, decreasing escape under typical conditionsMartian crustal magnetic fields affect local ion escape by at most 80%, decreasing escape under typical conditions We present a new method for estimating the influence of Martian crustal magnetic fields on ion escape Martian crustal magnetic fields affect global ion escape by at most 40%, decreasing escape under typical conditions Martian crustal magnetic fields affect local ion escape by at most 80%, decreasing escape under typical conditions

The canonical picture of the magnetotail of unmagnetized planets consists of draped interplanetary magnetic fields (IMFs) forming opposite‐directed lobes, separated by the current sheet. DiBraccio et al. (2018, https://doi.org/10.1029/2018GL077251) showed that Mars's magnetotail has a twist departing from this picture. Magnetohydrodynamic (MHD) results suggest that the asymmetry in how open field lines connected to the planet populate the tail causes the apparent twist. To validate this interpretation, we compare the tail topology determined from MHD simulations to that inferred from data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, in particular, how each topology responds to the upstream IMF orientation. The occurrence rates for open topology from both data and MHD vary with IMF polarities in a similar fashion as the tail twisting. This suggests that Mars's crustal fields have a global effect on the magnetosphere configuration, supporting the picture of a “hybrid” magnetotail that is partly induced/draped and partly intrinsic/planetary in origin. The interaction of the solar wind with unmagnetized planets, such as Venus, results in an induced magnetotail, which is formed by the interplanetary magnetic field lines draping around the planet, forming opposite‐directed lobes. Mars is similar to Venus in many aspects and was thought to have a similar tail configuration. A recent study, however, shows that Mars has a twist in its tail lobes and that modeling results suggest this twist is caused by the effects of its crustal magnetism. In this study, we use the superthermal electron measurements from MAVEN to infer the magnetotail topology resulting from the interaction between the solar magnetic fields and Mars's crustal fields, which is compared with the global magnetohydrodynamic model topology. Our results support the hypothesis that magnetic reconnection between crustal magnetic sources and the solar wind is responsible for the observed twist in Mars's tail lobes. This study provides a detailed mapping of tail magnetic topology at Mars, which is dominated by draped and open magnetic field linesBoth the MHD model and data show significant changes in Martian tail topology with respect to east/west IMFsIt implies that Mars's crustal fields have a global effect on the magnetosphere configuration, supporting the picture of a hybrid magnetotail