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We present a case study of plasma and magnetic field observations in the Martian magnetotail using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission during an orbit when the spacecraft was in the optical shadow, past the dusk terminator and downstream of the strongest crustal magnetic fields. In this region, we observed multiple magnetic field rotations (a signature of currents) closely associated with energized (up to 100 eV) electron populations. Several transitions between closed and draped magnetic topologies also occur in this region, which are likely to be caused by magnetic reconnection between the interplanetary magnetic field (IMF) and crustal magnetic fields. We also observe two regions of energized, counter‐streaming electrons, which are rare in the magnetotail, but twice as likely to occur downstream of strong crustal magnetic fields when they are near the evening terminator. Together, the multiple magnetic field rotations, topological changes, and counter streaming electrons suggest the presence of an electric potential structure similar to those observed above the auroral arc regions at Earth. Plain Language Summary: Mars does not have a global dipole magnetic field, but a fraction of the planet's crust carries strong remanent magnetization, which affects the plasma environment. When the magnetized solar wind encounters Mars, its magnetic field drapes around the conducting ionosphere and crustal magnetic fields and forms a magnetotail downstream of the planet. Reconnection between the solar wind magnetic field and crustal magnetic fields occurs often, resulting in a complex and changing configuration of open, closed, and draped magnetic field lines. Reconnection and reconfiguration of the magnetic field releases stored energy and drives currents, which energize the plasma. The energized plasma can precipitate onto the atmosphere and cause aurora. In this paper, we present a case study of plasma and magnetic field observations when the MAVEN spacecraft was downstream of strong crustal magnetic fields located near the evening terminator. Multiple magnetic field rotations, topological changes, and energized plasma indicate that reconnection gives rise to a complex magnetic environment downstream of the crustal fields. We found counter‐streaming electrons in the magnetotail, an observation which is thought to be a signature of the potential structure that energizes the auroral electrons, and are commonly observed at high altitudes above auroral regions at Earth. Therefore, we consider the observations in this study to be possible precursors to discrete auroral activity in Mars' crustal magnetic field regions. Key Points: The Martian magnetotail exhibits complex morphology and topology downstream of strong crustal magnetic field sourcesMultiple magnetic field rotations on spatial scales that are small compared to the magnetotail dimensions suggest multiple current regionsRare counter‐streaming electrons, are twice as likely to occur downstream of crustal fields when they are located near the dusk terminator [ABSTRACT FROM AUTHOR]

We present a statistical study of interchange injections in Saturn's inner and middle magnetosphere focusing on the dependence of occurrence rate and properties on radial distance, partial pressure, and local time distribution. Events are evaluated from over the entirety of the Cassini mission's equatorial orbits between 2005 and 2016. We identified interchange events from CHarge Energy Mass Spectrometer (CHEMS) H+ data using a trained and tested automated algorithm, which has been compared with manual event identification for optimization. We provide estimates of interchange based on intensity, which we use to investigate current inconsistencies in local time occurrence rates. This represents the first automated detection method of interchange, estimation of injection event intensity, and comparison between interchange injection survey results. We find that the peak rates of interchange occur between 7 and 9 Saturn radii and that this range coincides with the most intense events as defined by H+ partial particle pressure. We determine that nightside occurrence dominates as compared to the dayside injection rate, supporting the hypothesis of an inversely dependent instability growth rate on local Pedersen ionospheric conductivity. Additionally, we observe a slight preference for intense events on the dawnside, supporting a triggering mechanism related to large‐scale injections from downtail reconnection. Our observed local time dependence paints a dynamic picture of interchange triggering due to both the large‐scale injection‐driven process and ionospheric conductivity. Plain Language Summary: Studying high‐energy particles around magnetized planets is essential to understanding processes behind mass transport in planetary systems. Saturn's magnetic environment, or magnetosphere, is sourced from a large amount of low‐energy water particles from Enceladus, a moon of Saturn. Saturn's magnetosphere also undergoes large rotational forces from Saturn's short day and massive size. The rotational forces and dense internal mass source drive interchange injections, or the injection of high‐energy particles closer to the planet as low‐energy water particles from the inner magnetosphere are transported outward. There have been many strides toward understanding the occurrence rates of interchange injections, but it is still unknown how interchange events are triggered. We present a computational method to identify and rank interchange injections using high‐energy particle fluxes from the Cassini mission to Saturn. These events have never been identified computationally, and the resulting database is now publically available. We find that the peak rates of interchange occur between 7 and 9 Saturn radii and that this range coincides with the highest intensity events. We also find that interchange occurrence rates peak on the nightside of Saturn. Through this study, we identify the potential mechanisms behind interchange events and advance our understanding of mass transport around planets. Key Points: We developed a novel classification and identification algorithm for interchange injection based on Cassini CHEMS 3–220 keV H+ energetic ionsRadial occurrence rates and maximum partial H+ pressure in interchange peaked between 7 and 9 Saturn radii for all intensity categoriesOccurrence rates peak on the nightside (1800–0600 LT) as compared to the dayside (0600–1800 LT) [ABSTRACT FROM AUTHOR]