New Types of Electron Pitch Angle Distributions on Mars: Funnel and Skirt Distributions.

Using high‐resolution Solar Wind Electron Analyzer data from the Mars Atmosphere and Volatile EvolutioN spacecraft, we report two new types of electron pitch angle distributions (PADs) in the Martian plasma environment. The first type of electron PADs, showing pitch angle primally around 45° $45{}^{\circ}$, is termed funnel distribution, which was observed near the terminator and at about 1,200 km altitude. The second type of electron PADs, showing pitch angle primally around 135° $135{}^{\circ}$, is termed skirt distribution, which was detected on the nightside and at about 1,250 km altitude. The electrons of funnel and skirt distributions do not exhibit any photoelectron signatures and are shown to originate from the solar wind. Through the fitting analysis, we find that the electrons showing both funnel and skirt PADs are thermal electron populations and suprathermal electron populations. In addition, the possibilities that such two types of electron pitch angle distributions corresponding to magnetic field configurations are also discussed. Plain Language Summary: Electron pitch angle distribution (PAD) plays an important role in studying electron dynamics and magnetic field topologies. Various types of electron PADs in the Martian space environment have been widely reported and studied, including pancake, one‐sided loss cone, isotropy, double field‐aligned beam, butterfly, and so on. In this study, we report two new types of electron PADs, funnel and skirt distributions. The funnel distribution shows pitch angle primally around 45°, and the skirt distributions shows pitch angle primally around 135°. Additionally, we also analyze the sources and populations of these electrons showing funnel and skirt distributions, and discuss the magnetic field configurations that correlate to these two distributions. Such electron PADs may be important for understanding the Martian plasma environment, especially electron precipitation and ion escape. Key Points: In Martian space environment, we report two new types of electron pitch angle distributions, funnel and skirt distributionsThe funnel distribution shows pitch angles primally around 45° $45{}^{\circ}$, and the skirt distribution shows pitch angles primally around 135° $135{}^{\circ}$The electrons of funnel and skirt distributions are identified as thermal and suprathermal electron populations originating from solar wind [ABSTRACT FROM AUTHOR]