Energetic Electron Pitch-angle Distributions in the Martian Space Environment: Pancake

Abstract

We perform a statistical investigation of the occurrence rates of energetic electron (100–500 eV) pancake pitch-angle distributions (PADs) in the Martian space environment by utilizing 6 yr of MAVEN data. In the Martian ionosphere, we find the following: (1) at the same altitude in the terminator and night regions, the occurrences rates in the center of the southern magnetic anomaly regions are very low, but at the edges of strong magnetic fields, they increase significantly; (2) the occurrence rates of energetic electron perpendicular anisotropies on the Martian dayside increase with altitude; and (3) some closed magnetic lines in the 10°S–55°S, 30°W–125°W region at 400–800 km altitude gradually become open during the rotation of Mars from duskside to dawnside, while more closed magnetic lines are produced in the 40°S–65°S, 35°E–90°E region. In the Martian induced magnetosphere, we find the following: (1) the high-energy electron perpendicular anisotropy in the magnetosheath is the most significant; (2) the occurrence rates in the southern (Z MSO ≤−1 R M) magnetosheath are higher than those in the northern (Z MSO ≥ 1 R M) magnetosheath; (3) in the region of ∣Z MSO∣ < 0.5 R M, these high-energy electron pancake PADs are mainly concentrated in the magnetosheath region with Y MSO ∈ [−1.4RM, 2R M]; (4) the occurrence rates in the dawnside (Y MSO ≤−1 R M) magnetosheath are higher than those in the duskside (Y MSO ≥ 1 R M) magnetosheath; and (5) in the region of ∣Y MSO∣ < 0.5 R M, the occurrence rates throughout the magnetosheath are very high.

Betatron Acceleration of Suprathermal Electrons Upstream of the Martian Bow Shock

“…The events of interest were detected by MAVEN on 2016 September 13 and 2017 August 18, when the spacecraft was located upstream of the Martian bow shock (see the red star in Figures 1(a Figures 2(a)-(h) and (i)-(p), respectively. From top to bottom, Theoretically, the electrons energized by different acceleration mechanisms have quite distinct PADs (Fu et al 2011(Fu et al , 2013(Fu et al , 2014(Fu et al , 2020cLiu et al 2019;Wang et al 2019Wang et al , 2023aWang et al , 2023bZhao et al 2019;Guo et al 2021aGuo et al , 2023Yu et al 2022aYu et al , 2022bYu et al , 2023. Considering that the PAD of medium-energy electrons is clearly of pancake type and the timescale of this structure is much longer than the electron gyroperiod (the first adiabatic invariant v B 2 m ~^should be conserved), we can identify that the enhancement of electron flux intensity in this event is probably due to the betatron acceleration.…”

First Observation of Electron Rolling‐Pin Distribution in Jupiter's Magnetosphere

“…For example, the cigar distribution, created by the Fermi acceleration or betatron cooling, has been observed in the vicinity of reconnection X‐line, inside the growing flux pileup region (FPR), and away from the neutral sheet (Cao et al., 2017; Fu et al., 2011; Guo, Fu, Cao, Fan, et al., 2021; Liu et al., 2019; Wang et al., 2019). The pancake distribution, created by the betatron acceleration, has been observed inside growing FPRs and near the neutral sheet (Artemyev et al., 2012; Chen et al., 2019, 2021; Fu et al., 2013b, 2019a, 2020a; Grigorenko et al., 2016; Guo et al., 2023; Xu, Fu, Liu, & Wang, 2018; Yu et al., 2022b). The butterfly distribution, created by combination of Fermi and betatron acceleration or the magnetic mirror effect, has been observed inside expanding flux tubes in magnetotail and in the near‐Earth transition region (Wang et al., 2019; Yu et al., 2023).…”