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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 particle responsible for producing these detectable aurorae, that is accelerated electrons or hotter solar wind electrons (termed “auroral electrons"). By utilizing empirical criteria to select auroral electrons established by Xu et al. [2022], we conduct statistical analyses of the impact of upstream drivers on the occurrence rate and electron fluxes of auroral electrons. We find the occurrence rate is well organized and increases with upstream dynamic pressure and weakly depends on the interplanetary magnetic field strength. Meanwhile, the integrated auroral electron flux is somewhat insensitive to the upstream drivers. In the meantime, the auroral emission is not the sole effect of electrons impacting the collisional atmosphere. Auroral electrons are expected to cause significant ionization and enhance the plasma density locally. In this study, we also quantify the ionospheric impact of auroral electron precipitation, specifically the thermal ion (O+, O2+, CO2+) density enhancement, with MAVEN observations and also modeling. Our results show the ion density to increase up to 1-2 orders of magnitude at low altitudes.

The Martian crustal magnetic anomalies create a varied, asymmetric obstacle for the draped interplanetary magnetic field (IMF) to interact with. One possible result of this interaction is magnetic reconnection, a process by which anti-parallel magnetic field lines connect and reconfigure, transferring energy into the surrounding environment and mixing previously separated plasma populations. Here, we present an analysis to determine the draped IMF conditions that favor reconnection with the underlying crustal anomalies at Mars. First, we plot a map of the crustal anomalies’ strength and orientation compiled from magnetic field data taken throughout the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Second, we create “shear maps” which calculate and plot the angle of shear between the transverse component of the anomalies and a chosen overlaid draping direction. Third, we define a “shear index” which quantifies the susceptibility of a particular region to undergo reconnection based on a given draped IMF orientation and the resulting shear map for that region. We then compare the shear index for a variety of draped field orientations within different regions of the Martian magnetosphere. Our results suggest eastward/westward (horizontal) draped fields present regions that are more likely for anti-parallel magnetic reconnection to occur with the crustal anomalies than northward/southward (vertical) draped fields, with one notable exception being the strongest crustal anomalies located in the southern hemisphere ~180° longitude. An east/west draped field roughly corresponds to a +/- By IMF direction on the dayside, implying the rate of magnetic reconnection on the dayside of Mars may be enhanced for IMF field lines pointing in the +/- YMSO direction compared to that of IMF field lines pointing in the +/- ZMSO direction, with MSO referring to the Mars Solar Orbital coordinate system. Understanding the interplay between Mars’s crustal magnetic fields and the IMF is crucial to answer outstanding science questions regarding nightside magnetospheric activity at Mars, namely how IMF orientation affects the twisting of the magnetotail, open magnetic topology observations on the nightside, and discrete aurora observations in the southern hemisphere.

At Mars, recent studies based on a combination of MAVEN data and modeling have determined the Martian magnetotail exhibits a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, away from the nominal interplanetary magnetic field (IMF) draping morphology. An initial study by DiBraccio et al. [2018] employed MAVEN magnetic field measurements, coupled with MHD simulations, to indicate that the twist is likely a result of the sun-planetary interaction. Now with several more years of MAVEN data available, we augment this work using a statistical analysis of MAVEN magnetic field data from November 2014 through November 2019. We utilized ~6000 orbits, requiring that MAVEN observed both the magnetotail and the upstream IMF over a given orbit. For periods when the upstream IMF measurements were not available due to MAVEN’s orbit precession, we utilize an IMF proxy to determine characteristics of the upstream orientation. The location of the magnetotail lobes, identified in the data as the regions of magnetic field behind the planet directed towards and away from Mars, are analyzed as a function of the upstream IMF dawn-dusk component. In the previous DiBraccio et al. [2018] study, this dawn-dusk component was found to be the separating factor in the direction of magnetotail twisting. To quantify the degree of tail twisting for a given scenario, we determine the vector between the center of the towards/away tail lobes and calculate the angle between this vector and the expected direction for nominal IMF draping. This calculated tail twist angle is then assessed as a function of a variety of factors including strong crustal field location, Mars season, and downtail distance. In all cases, we determine that the degree of tail twisting is larger when the IMF is oriented in the duskward direction, suggesting enhanced coupling between the IMF and planetary crustal fields. Furthermore, we demonstrate that the degree of tail twisting exhibits different trends for crustal field orientation under dawnward versus duskward IMF configurations. Seasonal variations indicate that tail twisting may vary over the course of the Martian year, but additional data are needed during the northern fall and winter periods for confirmation. Finally, when assessing the tail twist with downtail distance we find that the degree of twisting increases with distance from the planet. This result is similar to Earth where observations of the magnetotail twist increases away from the planet as the torque exerted by the IMF on the planetary field increases. From these findings we confirm that the tail twist at Mars is likely a result of the direct interaction between the IMF and the planetary crustal fields; however, we find evidence suggesting that the degree of twisting is larger for duskward IMF orientations. This implies that magnetic reconnection on the dayside of Mars, between the IMF and crustal fields, may be favorable under specific IMF configurations.