Empirically Determined Auroral Electron Events at Mars—MAVEN Observations

Abstract

Discrete aurorae have been observed at magnetized planets such as Earth and Jupiter, triggered by accelerated electrons. Similar aurorae have also been observed at Mars with only localized strong crustal magnetisms. However, our understanding of this phenomenon at Mars is still limited. In particular, direct and quantitative comparisons of the auroral and its source electron events are lacking as these two types of observations are usually made at different times and/or locations. In this study, we establish empirical criteria to select electron events (“auroral electrons”) that could trigger detectable auroral emissions with Mars Atmosphere and Volatile EvolutioN measurements, thereby enabling a direct statistical comparison. We find auroral electrons share similar statistical characteristics to those previously reported for discrete auroral events. This study bridges the gap between electron observations and auroral detections and enables collaborations across different Mars missions, as well as comparative planetary studies of discrete aurora.

Nightside Auroral Electrons at Mars: Upstream Drivers and Ionospheric Impact

“…Building on Xu et al. (2022), we apply the same selection criteria to identify auroral electrons and determine how the upstream drivers affect their occurrence rates and also the integrated electron fluxes. Furthermore, auroral electron impact can cause effects other than observable auroral emission, one of which is the enhanced local ionization and thus local ion densities.…”

“…Discrete aurora and its source electrons have both been observed and studied at Mars. Building on Xu et al (2022), we apply the same selection criteria to identify auroral electrons and determine how the upstream drivers affect their occurrence rates and also the integrated electron fluxes. (d) The ratio between median ion densities measured when integrated electron fluxes are above and below 1.1 × 10 10 eV cm −2 s −1 sr −1 , different colors for different ion species.…”

“…We select auroral electron events by applying these criteria to suprathermal electron measurements by the Solar Wind Electron Analyzer (SWEA) (Mitchell et al., 2016) from 1 December 2014 to 1 April 2020, limited to solar zenith angle (SZA) >95° (following Xu et al. (2022)) and an altitude range of 150–500 km. One‐sided loss cone distributions are selected by comparing upward and downward electron fluxes to perpendicular electron fluxes within 100–300 eV (Weber et al., 2017; Xu, Weber, et al., 2019).…”

“…At Mars, "discrete aurora" is defined more specifically for localized emissions, in contrast to global auroral emissions (Schneider et al, 2015). Several studies have associated these localized emissions with energized electron observations (Brain et al, 2006;Gérard et al, 2015;Leblanc et al, 2008;Soret et al, 2016Soret et al, , 2021Xu et al, 2020Xu et al, , 2022. The reported energization processes/mechanisms at Mars include, but are not limited to, narrow electrostatic potential layers (associated with inverted-V electron events) (e.g., Brain et al, 2006;Xu et al, 2020), energization associated with current sheet crossings (e.g., Halekas et al, 2008;Harada et al, 2020), and a hotter electron temperature (without acceleration by an electrostatic potential) (Akbari et al, 2019) perhaps caused by wave-particle interaction (e.g., Fowler et al, 2020Fowler et al, , 2021.…”

First Synoptic Images of FUV Discrete Aurora and Discovery of Sinuous Aurora at Mars by EMM EMUS

“…Within this region, discrete aurora occurs more frequently on the dusk side and for westward interplanetary magnetic field (IMF) directions (Schneider et al, 2021) with no significant dependence on local time or IMF direction in other regions. Xu et al (2022) showed that accelerated electron events share the same characteristics (locations, crustal field, etc.) as the auroral events, establishing a causal connection.…”