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We present a comprehensive study of the nightside aurora phenomenon on Mars, utilizing observations from EMUS onboard Emirates Mars Mission. The oxygen emission at 130.4 nm is by far the brightest FUV auroral emission line observed at Mars. Our statistical analysis reveals geographic, solar zenith angle, local time, and seasonal dependencies of auroral occurrence. Higher occurrence of aurora is observed in regions of open magnetic topology, where crustal magnetic fields are either very weak or both strong and vertical. Aurora occurs more frequently closer to the terminator and is more likely on the dusk side than on the dawn side of the night hemisphere. A pronounced auroral feature appears close to midnight local times in the southern hemisphere, consistent with the spot of energetic electron fluxes previously identified in the Mars Global Surveyor data. This auroral spot is more frequent after midnight than before. Additionally, some regions on Mars are “aurora voids” where essentially no aurora occurs. Aurora exhibits a seasonal dependence, with a major enhancement near perihelion. Non–crustal field aurora additionally shows a secondary enhancement near Ls30°. This seasonal variability is a combination of the variability in ionospheric photoelectrons and thermospheric atomic oxygen abundance. Auroral occurrence also shows an increase with the rise of Solar Cycle 25. The brightest auroral pixels are observed during space weather events such as Coronal Mass Ejections and Stream Interaction Regions. These observations not only shed light on where and when Martian aurora occurs, but also add to our understanding of Mars' magnetic environment and its interaction with the heliosphere. In this study, we explore the phenomenon of aurora on the nightside of Mars, using observations from the highly sensitive Emirates Mars Ultraviolet Spectrometer (EMUS) on the Emirates Mars Mission. Our analysis reveals distinct patterns in auroral occurrence on the planet. For instance, there is a higher rate of auroral activity in regions where Mars' magnetic field lines are open (i.e., connected to the collisional atmosphere at one end). We also found that aurora is more common near the terminator (with the occurrence decreasing as the solar zenith angle increases), and particularly during the evening hours, as opposed to early morning. Interestingly, these auroral events also show a seasonal dependence, peaking around perihelion in a Martian year, when Mars is closest to the sun. This seasonal pattern corresponds with the variation of photoelectrons in Mars' dayside ionosphere and the atomic oxygen abundance in the thermosphere. Auroral occurrence increases with increasing solar activity. Also, the auroral brightness increases during space weather events. Our study not only gives us a clearer picture of where and when the aurora occurs on Mars but also hints at the underlying processes influencing them, offering insights into the planet's magnetic and charged particle environment. Higher auroral occurrence is observed in regions of open magnetic topology, where crustal fields are either very weak or primarily verticalAurora occurs more frequently near the terminator compared to deep night, with higher occurrence at dusk than at dawnAurora occurs more frequently near perihelion, with the brightest auroral pixels observed during space weather events Higher auroral occurrence is observed in regions of open magnetic topology, where crustal fields are either very weak or primarily vertical Aurora occurs more frequently near the terminator compared to deep night, with higher occurrence at dusk than at dawn Aurora occurs more frequently near perihelion, with the brightest auroral pixels observed during space weather events

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

We present a study of changes in Martian magnetic topology induced by upstream solar wind ram pressure variations. Using electron energy spectra and pitch angle distributions measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we classify the topology of magnetic field lines in the Martian space environment across a range of solar wind conditions. We find that during periods of high solar wind dynamic pressure, draped fields are pushed to lower altitudes on the dayside of the planet, compressing closed fields. At the same time, open topology becomes more prevalent on the nightside due to the broadening of crustal cusp regions. The result is a decrease in closed topology at all locations around Mars, suggesting that the Martian ionosphere becomes significantly more exposed to solar wind energy input during high solar wind pressure. This could likely contribute to elevated levels of ion escape during these periods. Planetary atmospheres are constantly bombarded by energy and radiation from the Sun, and over time this energy input can strip away an atmosphere to space. This process has been particularly devastating at Mars, where the loss of most of its original atmosphere has left the planet cold and desolate. This loss may have been in part due to the planet's lack of a global magnetic field. While the Earth possesses a large magnetic field that diverts much of the solar energy input, Mars does not. However, Mars does possess smaller pockets of magnetic field that are rooted in the planet's crust and extend outward through the atmosphere, a unique feature in the solar system. These magnetic fields are able to shield Mars's atmosphere on a small scale but are susceptible to changes in the strength of solar activity. Here we show that during these periods of increased solar output, the magnetic pockets across Mars are compressed to a smaller size, leaving the planet's atmosphere more exposed and more likely to escape to space. High solar wind pressure decreases the presence of closed topology across MarsOn the dayside, draped fields extend to lower altitudes during high solar wind pressureOn the nightside, crustal cusps with open topology expand during high solar wind pressure

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

Many aspects of the Sun‐Mars interaction have been investigated during solar transient events with measurements from multiple spacecrafts and also simulation efforts. Limited discussion has been paid to magnetic topology response to disturbed upstream conditions. The implications of topology changes include, but are not limited to, the pattern of energetic particle precipitation into the Martian atmosphere and the impact on cold ion escape during solar transient events as low‐energy ion escape is dependent on magnetic topology. In this study, we investigate the magnetic topology response to the 2017 September interplanetary coronal mass ejection (ICME) event with measurements collected by the Mars Atmospheric and Volatile EvolutioN spacecraft. It is found that the interface between draped interplanetary magnetic field and closed field lines was moved from 800–1400 km in altitude during quiet conditions to 200–400 km after ICME arrived at Mars and then relaxed back to high altitudes again after the event. To gain insight into magnetic topology response on a global scale, we first validate magnetic topology from a time‐dependent simulation with a single‐fluid multispecies magnetohydrodynamic (MHD) model by comparing magnetic topology determined from Mars Atmospheric and Volatile EvolutioN data, which shows a good agreement. Then we present MHD predictions of global magnetic topology changes during this ICME event. In addition to a deeper interplanetary magnetic field penetration, MHD results suggest more open field lines in response to the ICME event. An important way for Mars to lose its atmosphere over time is through solar wind striping away ions from Mars. The planet lacks of an intrinsic global magnetic field but possesses localized crustal fields so that solar wind and the interplanetary magnetic field have direct access to the Martian ionosphere. This effect is intensified when a coronal mass ejection is emitted from the Sun and hits Mars. Charged particles subject to electromagnetic forces so that the magnetic topology, whether a magnetic field line connects to Mars and/or solar wind, is an important aspect of the Sun‐Mars interaction and also closely related to energy and particle transport at Mars and low‐energy ion escape. In this study, we investigate how the Martian magnetic topology responds to the coronal mass ejection event occurred in September 2017 with measurements from the Mars Atmosphere Volatile and Evolution spacecraft and also simulation results from a magnetohydrodynamic model. It is found that during the event, interplanetary magnetic field penetrates deeper into the atmosphere and also there are more magnetic field lines connecting Mars and solar wind, which means ions subject to escape starting from lower altitudes, where ion densities are higher. From MAVEN data, IMF is found to penetrate deeper over the northern hemisphere due to enhanced solar wind dynamic pressure during the ICMETopology from MHD shows a good agreement with data and provides insights into a global responseMHD results suggest deeper IMF penetration and more open field lines during the ICME event

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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

Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross‐tail current sheet is rotated away from the expected location for a Venus‐like induced magnetotail based on nominal IMF draping. Data‐model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth. This study investigates the magnetic environment of Mars in order to understand how its structure is different from that of other planets. In the past, it was thought that the Sun's magnetic field interacts with Mars in a similar way to a comet or Venus. This would imply that the magnetic field geometry could be easily predicted; however, recent investigations have found that this is not the case. This work includes both simulation and MAVEN data to determine that the magnetic environment of Mars is much different than this original picture. The conclusions find that these fields are twisted from their expected geometry, suggesting a difference in the interaction between Mars and the Sun. Because atmospheric particles are able to travel along these magnetic fields, this unique geometry may have great implications for atmospheric loss at Mars. MAVEN data and simulations confirm that a twisted field configuration is present in the Martian magnetotail that is highly dependent on IMF BYOpen fields, likely created by magnetic reconnection between Mars crustal fields and the IMF, occupy a majority of the twisted tail lobesComparisons with Earth suggest that the dipolar component of Mars' crustal fields play a crucial role in altering the magnetotail structure

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

The magnetic field draping pattern in the magnetosheath of Mars is of interest for what it tells us about both the solar wind interaction with the Mars obstacle and the use of the field measured there as a proxy for the upstream interplanetary magnetic field (IMF) clock angle. We apply a time‐dependent, global magnetohydrodynamic model toward quantifying the spatial and temporal variations of the magnetic field draping direction on the Martian dayside above 500‐km altitude. The magnetic field and plasma are self‐consistently solved over one Mars rotation period, with the dynamics of the field morphology considered as the result of the rotation of the crustal field orientation. Our results show how the magnetic field direction on the plane perpendicular to the solar wind flow direction gradually departs from the IMF as the solar wind penetrates toward the obstacle and into the tail region. This clock angle departure occurs mainly inside the magnetic pileup region and tailward of the terminator plane, exhibiting significant dawn‐dusk and north‐south asymmetries. Inside the dayside sheath region, the field direction has the greatest departure from the IMF‐perpendicular component direction downstream of the quasi‐parallel bow shock, which for the nominal Parker spiral is over the dawn quadrant. Thus, the best region to obtain an IMF clock angle proxy is within the dayside magnetosheath at sufficiently high altitudes, particularly over subsolar and dusk sectors. Our results illustrate that the crustal field has only a mild influence on the magnetic field draping direction within the magnetosheath region. According to the classic magnetic field draping theory, when the solar wind plasma encounters unmagnetized planetary bodies, the entrained interplanetary magnetic field (IMF) would pile up and drape around as the flow is diverted. Under this approximation, the draped field lines maintain an orientation similar to the upstream IMF in the plane perpendicular to the solar wind flow direction. However, the real morphology of the magnetic field draping at Mars has been poorly understood. In this study, we apply a state‐of‐the‐art global model to investigate the degree of distortion of the draped field lines when the complex Mars‐solar wind interaction is self‐consistently accounted for. Our results illustrate that when the IMF penetrates the magnetosheath edge into lower altitudes, the magnetic field lines may be so distorted and bent that their directions significantly deviate from the expectation from the classic field draping scenario. Our study reinforces the need to change any remaining notion of Mars in field line draping as a nonmagnetic planet. Moreover, this work presents a practical approach for inferring the IMF direction when direct measurements of the pristine solar wind are not available. The clock angle of the field within the dayside magnetosheath is a reasonable proxy for the IMFThe magnetic field clock angle departure increases with decreasing altitude and increasing SZAThe draping direction departure is the greatest downstream of the quasi‐parallel bow shock

Field‐aligned electrostatic potentials in the Martian ionosphere play potentially important roles in maintaining current systems, driving atmospheric escape and producing aurora. The strength and polarity of the potential difference between the observation altitude and the exobase (~180 km) determine the energy dependence of electron pitch angle distributions (PADs) measured on open magnetic field lines (i.e. those connected both to the collisional atmosphere and to the interplanetary magnetic field). Here we derive and examine a data set of ~3.6 million measurements of the potential between 185 km and 400 km altitude from PADs measured by the Mars Global Surveyor Magnetometer/Electron Reflectometer experiment at 2 A.M./2 P.M. local time from May 1999 to November 2006. Potentials display significant variability, consistent with expected variable positive and negative divergences of the convection electric field in the highly variable and dynamic Martian plasma environment. However, superimposed on this variability are persistent patterns whereby potential magnitudes depend positively on crustal magnetic field strength, being close to zero where crustal fields are weak or nonexistent. Average potentials are typically positive near the center of topologically open crustal field regions where field lines are steeper, and negative near the edges of such regions where fields are shallower, near the boundaries with closed fields. This structure is less pronounced for higher solar wind pressures and (on the dayside) higher solar EUV irradiance. Its causes are uncertain at present but may be due to differential motion of electrons and ions in Mars's substantial but (compared to Earth) weak magnetic fields. The Aurora Borealis, or northern lights, occur when high‐energy electrons from space collide violently with our upper atmosphere. These electrons receive their energy from strong electric fields that accelerate them downward along the force lines of the earth's global magnetic field. On Mars, accelerated electrons are also responsible for the aurora that has been observed by both the Mars Express and MAVEN spacecraft. In this study we use the observed properties of upward‐ and downward‐traveling electrons measured by the Mars Global Surveyor spacecraft to deduce the strength of these important electric fields. We find that they are highly variable, as is to be expected from the dynamic interaction of the solar wind (a stream of charged particles constantly ejected by the sun) with the Mars upper atmosphere. However, these electric fields also show persistent patterns in regions where Mars' crustal rocks are most strongly and coherently magnetized. Here, the electric fields are predominantly downward where the magnetic field lines are more horizontal and predominantly upward where they are more vertical. Detailed modeling and further observations will be required to fully understand the plasma dynamics behind this phenomenon. Field‐aligned electrostatic potentials are derived from energy dependence of electron loss cones measured at ~400 km altitudeStrong potentials are associated with crustal magnetic fields: positive (negative) potentials for shallow (steep) magnetic elevation anglesPotential structures also vary with solar zenith angle, solar wind pressure, and EUV irradiance; explanation awaits detailed modeling

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

We analyze Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of magnetic flux ropes embedded in Martian magnetotail current sheets, in order to evaluate the role of magnetotail reconnection in their generations. We conduct a minimum variance analysis to infer the generation processes of magnetotail flux ropes from the geometrical configuration of the individual flux rope axial orientation with respect to the overall current sheet. Of 23 flux ropes detected in current sheets in the near‐Mars (∼1–3 Martian radii downstream) magnetotail, only 3 (possibly 4) can be explained by the magnetotail reconnection scenario, while the vast majority of the events (19 events) are more consistent with flux ropes that are originally generated in the dayside ionosphere and subsequently transported into the nightside magnetotail. The mixed origins of the detected flux ropes imply complex nature of generation and transport of Martian magnetotail flux ropes. Instances of magnetic flux ropes within near‐Mars magnetotail current sheets are observed that have a wide variety of orientationsOnly 3 of the 23 flux ropes analyzed here have orientations within 30 degrees of the cross‐tail current directionMajority has large angles to the cross‐tail current direction consistent with those formed in ionosphere and transported into magnetotail

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

Several letters to the editor are presented in response to articles in previous issues related to politics and government, including the congressional uproar about gambling, a lecture on the United Nations, and a story about the Clameur de Haro in the Isle of Guernsey.

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

We present initial results of strong field amplitude flux ropes observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission around Mars during the interplanetary coronal mass ejection (ICME) passage on 8 March 2015. The observed durations were shorter than 5 s and the magnetic field magnitudes peaked above 80 nT, which is a few times stronger than those usually seen in the magnetosheath barrier. These are the first unique observations that MAVEN detected such flux ropes with a strong field at high altitudes (>5000 km). Across these structures, MAVEN coincidentally measured planetary heavy ions with energies higher than a few keV. The spatial properties inferred from the Grad‐Shafranov equation suggest that the speed of the structure can be estimated at least an order of magnitude faster than those previously reported quiet‐time counterparts. Hence, the space weather event like the ICME passage can be responsible for generating the observed strong field, fast‐traveling flux ropes. MAVEN detected strong field amplitude flux ropes in the magnetosheath during ICME passage in March 2015Such strong flux ropes (>80 nT) are first detected at the high altitudes (>5000 km) at MarsEstimated traveling velocity of flux ropes is at least an order of magnitude faster than usual cases

Graphical Abstract:

The Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars orbiter has been gathering information on the Mars upper atmosphere, ionosphere, and solar and solar wind interactions since its orbit insertion in September 2014. MAVEN's science goals are to understand processes driving the escape of atmospheric gases to space at the present epoch, and their variations with solar and local heliospheric conditions together with geographical and seasonal influences. This introduction and the accompanying articles provide a selection of key results obtained up to the time of writing, including measurements of the overall geometry and variability of the Martian magnetosphere, upper atmosphere, and ionosphere and their responses to interplanetary coronal mass ejections and solar energetic particle influxes. The ultimate goal is to use these results to determine the integrated loss to space through time and its role in overall Mars atmosphere evolution. MAVEN science results at Mars affect our understanding of the history of Mars volatilesResults integrate all aspects of the Mars upper atmosphere system

The nucleus of comet C/2013 A1 (Siding Spring) passed within 141,000 km of Mars on 19 October 2014. Thus, the cometary coma and the plasma it produces washed over Mars for several hours producing significant effects in the Martian magnetosphere and upper atmosphere. We present observations from Mars Atmosphere and Volatile EvolutioN's (MAVEN's) particles and field's instruments that show the Martian magnetosphere was severely distorted during the comet's passage. We note four specific major effects: (1) a variable induced magnetospheric boundary, (2) a strong rotation of the magnetic field as the comet approached, (3) severely distorted and disordered ionospheric magnetic fields during the comet's closest approach, and (4) unusually strong magnetosheath turbulence lasting hours after the comet left. We argue that the comet produced effects comparable to that of a large solar storm (in terms of incident energy) and that our results are therefore important for future studies of atmospheric escape, MAVEN's primary science objective. Comet Siding Spring's coma and plasma engulfed Mars on 19 October 2014The comet's plasma very likely severely distorted the Martian magnetosphereThe comet might have driven atmospheric escape like a strong solar storm

Simultaneous Mars Atmosphere and Volatile EvolutioN mission (MAVEN) plasma and magnetic field observations reveal a detached magnetic flux rope in the Martian induced magnetosphere. The flux rope was identified by an increase in the magnetic field amplitude accompanied by smooth vector rotations. In addition, MAVEN observed a pronounced ion composition change across the structure, with solar wind ions dominating outside and planetary ions dominating within. Grad‐Shafranov reconstruction is applied to determine the two‐dimensional spatial structure of the flux rope. The event occurred near the dusk terminator, downstream from strong crustal magnetic fields. One possibility is that the flux rope was created by magnetic reconnection associated with interplanetary and/or crustal magnetic fields. A weak interplanetary coronal mass ejection (ICME) arrived at Mars a few hours before the event. A pressure pulse and turbulent magnetic fields due to the ICME might be responsible for driving magnetic reconnection to detach the flux rope from the crustal source. First detection by MAVEN of a detached flux rope at MarsDetached flux rope includes planetary origin heavy ion populationsObserved location is downstream from the strong crustal magnetic fields

We report on the complex nature of the induced Martian magnetotail using simultaneous magnetic field and plasma measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Two case studies are analyzed from which we identify (1) repetitive loading and unloading of tail magnetic flux as the field magnitude changes dramatically, exhibiting signatures similar to substorm activity within intrinsic magnetospheres; (2) multiple current sheet crossings indicative of plasma sheet flapping; (3) tailward flowing high‐energy planetary ions (O+and O2+), confined exclusively to the cross‐tail current sheet, contributing to atmospheric escape; and (4) signatures of magnetic flux ropes, suggesting the occurrence of tail reconnection. These events illustrate the complexity of the Martian magnetotail as MAVEN provides key observations relevant to the unanswered questions of induced magnetosphere dynamics. Initial MAVEN observations demonstrate dynamics of the complex Martian magnetotailObserved substorm‐like loading/unloading of magnetic flux with signatures of magnetic reconnectionEscaping high‐energy planetary ions are observed exclusively in tail current sheet

We study the solar wind interaction with the Martian upper atmosphere during the 8 March 2015 interplanetary coronal mass ejection (ICME) by using a global multifluid MHD model. Comparison of the simulation results with observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft shows good agreement. The total ion escape rate is increased by an order of magnitude, from 2.05 × 1024s−1(pre‐ICME phase) to 2.25 × 1025s−1(ICME sheath phase), during this time period. Two major ion escape channels are illustrated: accelerated pickup ion loss through the dayside plume and ionospheric ion loss through the nightside plasma wake region. Interestingly, the tailward ion loss is significantly increased at the ejecta phase. Both bow shock and magnetic pileup boundary (BS and MPB) locations are decreased from (1.2RM, 1.57RM) at the pre‐ICME phase to (1.16RM, 1.47RM), respectively, during the sheath phase along the dayside Mars‐Sun line. Furthermore, both simulation and observational results indicate that there is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km, i.e., the photochemical region) during this event. The total ion escape rate is increased by an order of magnitude during the 8 March ICMEThe tailward ion loss is significantly increased at the ejecta phaseThere is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km)

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

Hand hygiene in hospitals is vital to limit the spread of infections. This study aimed to identify key beliefs underlying hospital nurses' hand-hygiene decisions to consolidate strategies that encourage compliance. Informed by a theory of planned behaviour belief framework, nurses from 50 Australian hospitals (n = 797) responded to how likely behavioural beliefs (advantages and disadvantages), normative beliefs (important referents) and control beliefs (barriers) impacted on their hand-hygiene decisions following the introduction of a national ‘5 moments for hand hygiene’ initiative. Two weeks after completing the survey, they reported their hand-hygiene adherence. Stepwise regression analyses identified key beliefs that determined nurses' hand-hygiene behaviour. Reducing the chance of infection for co-workers influenced nurses' hygiene behaviour, with lack of time and forgetfulness identified as barriers. Future efforts to improve hand hygiene should highlight the potential impact on colleagues and consider strategies to combat time constraints, as well as implementing workplace reminders to prompt greater hand-hygiene compliance. Rather than emphasising the health of self and patients in efforts to encourage hand-hygiene practices, a focus on peer protection should be adopted and more effective workplace reminders should be implemented to combat forgetting.

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 present the first measurements of Mars discrete aurora in the extreme ultraviolet (<110 nm) and the first synoptic aurora images in the far ultraviolet (110–180 nm). Auroral emission is detected in >75% of nightside images, with patterns shifting visibly over 15–20 min. Aurora is observed most frequently in regions of open magnetic topology (where crustal magnetic fields are very weak and/or vertical), with the brightest aurora where crustal fields are strongest. We present the first disk‐averaged spectrum of discrete aurora, with several O, C, and CO features as expected for electron impact primarily on CO2. We categorize discrete auroral morphology into three types: crustal field aurora, non‐crustal field patchy aurora, and a new type we call “sinuous” aurora, an elongated serpentine structure that stretches thousands of kilometers into the nightside from near midnight in the northern hemisphere. These observations point to a highly dynamic environment in Mars' magnetotail. In this study, we present near‐global images of localized aurora on Mars and the first measurements of these aurora at very short ultraviolet wavelengths (<110 nm). They are caused by energetic electrons from the solar wind smashing into Mars’ upper atmosphere. We find auroras in >75% of images, with their patterns shifting visibly over 15–20 min. They are observed most frequently in regions where magnetic fields are very weak or both strong and vertical, with the brightest aurora where magnetic fields are strongest. We present the first disk‐averaged spectrum of these auroras, showing features expected for electrons striking CO2(the most abundant gas in Mars’ atmosphere). We categorize discrete auroral patterns into three types: those near strong vertical crustal magnetic field, patchy aurora near very weak crustal fields, and a new type we call “sinuous,” an elongated serpentine structure that stretches thousands of kilometers into the nightside from near midnight in the northern hemisphere. These observations point to a highly dynamic environment in Mars’ nightside space environment. We present the first disk measurements of Mars discrete aurora in the EUV end FUV, with the oxygen feature at 130.4 nm being the brightestAuroras are detected in ∼75% of nightside images and are more likely where crustal fields are either very weak or both strong and verticalAn elongated, sinuous discrete aurora is discovered, extending far into the nightside. It may be related to the magnetotail current sheet We present the first disk measurements of Mars discrete aurora in the EUV end FUV, with the oxygen feature at 130.4 nm being the brightest Auroras are detected in ∼75% of nightside images and are more likely where crustal fields are either very weak or both strong and vertical An elongated, sinuous discrete aurora is discovered, extending far into the nightside. It may be related to the magnetotail current sheet

BackgroundInterventions that prevent healthcare-associated infection should lead to fewer deaths and shorter hospital stays. Cleaning hands (with soap or alcohol) is an effective way to prevent the transmission of organisms, but rates of compliance with hand hygiene are sometimes disappointingly low. The National Hand Hygiene Initiative in Australia aimed to improve hand hygiene compliance among healthcare workers, with the goal of reducing rates of healthcare-associated infection.MethodsWe examined whether the introduction of the National Hand Hygiene Initiative was associated with a change in infection rates. Monthly infection rates for healthcare-associated Staphylococcus aureusbloodstream infections were examined in 38 Australian hospitals across 6 states. We used Poisson regression and examined 12 possible patterns of change, with the best fitting pattern chosen using the Akaike information criterion. Monthly bed-days were included to control for increased hospital use over time.ResultsThe National Hand Hygiene Initiative was associated with a reduction in infection rates in 4 of the 6 states studied. Two states showed an immediate reduction in rates of 17% and 28%, 2 states showed a linear decrease in rates of 8% and 11% per year, and 2 showed no change in infection rates.ConclusionsThe intervention was associated with reduced infection rates in most states. The failure in 2 states may have been because those states already had effective initiatives before the national initiative’s introduction or because infection rates were already low and could not be further reduced.

Introduction Interventions that prevent healthcare-associated infections should lead to fewer deaths and shorter hospital stays. Cleaning hands with soap and water or alcohol rub is an effective way to prevent the transmission of organisms, but compliance is sometimes low. The National Hand Hygiene Initiative in Australia aimed to improve hand hygiene compliance among healthcare workers, with the goal of reducing rates of healthcare-associated infections. Methods We examined if the introduction of the National Hand Hygiene Initiative was associated with a change in infection rates. Monthly infection rates for six types of healthcare-associated infections were examined in 38 Australian hospitals across six states. Infection categories were: bloodstream infections, central-line associated bloodstream infections, methicillin-resistant and methicillin-sensitive Staphylococcus aureus, Staphylococcus aureus bacteraemia and surgical site infections. Results The National Hand Hygiene Initiative was associated with a statistically significant reduction in infection rates in 11 out of 23 state and infection combinations studied. There was no change in infection rates for nine combinations, and there was an increase in three infection rates in South Australia. Conclusions The intervention was associated with reduced infection rates in many cases. The lack of improvement in nine cases may have been because they already had effective initiatives before the national initiative’s introduction.

The Martian magnetotail exhibits a highly twisted configuration, shifting in response to changes in polarity of the interplanetary magnetic field's (IMF) dawn‐dusk (BY) component. Here, we analyze ∼6000 MAVEN orbits to quantify the degree of magnetotail twisting (θTwist) and assess variations as a function of (a) strong planetary crustal field location, (b) Mars season, and (c) downtail distance. The results demonstrate that θTwistis larger for a duskward (+BY) IMF orientation a majority of the time. This preference is likely due to the local orientation of crustal magnetic fields across the surface of Mars, where a +BYIMF orientation presents ideal conditions for magnetic reconnection to occur. Additionally, we observe an increase in θTwistwith downtail distance, similar to Earth's magnetotail. These findings suggest that coupling between the IMF and moderate‐to‐weak crustal field regions may play a major role in determining the magnetospheric structure at Mars. MAVEN magnetic field data are analyzed to understand factors that may influence the magnetotail structure at Mars. The Martian magnetotail lobes are observed to be twisted and the degree of this twist can vary. In this work, we calculate the degree of tail twist and monitor how it changes. To understand how the twist changes, we examine these variations as a function of Mars crustal field location, Mars season, and downtail distance away from Mars. Mars' magnetotail can be twisted up to 60 deg away from its expected location based on interplanetary magnetic field (IMF) draping, much greater than Earth's tail twistMAVEN observations show that Mars' tail exhibits larger twisting for +BYIMF orientation, compared to −BYIMFMars crustal magnetic fields may play a significant role in shaping the twisted structure of the Martian magnetotail Mars' magnetotail can be twisted up to 60 deg away from its expected location based on interplanetary magnetic field (IMF) draping, much greater than Earth's tail twist MAVEN observations show that Mars' tail exhibits larger twisting for +BYIMF orientation, compared to −BYIMF Mars crustal magnetic fields may play a significant role in shaping the twisted structure of the Martian magnetotail

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