The Influence of Magnetic Field Topology and Orientation on the Distribution of Thermal Electrons in the Martian Magnetotail

TL;DR

This study analyzes MAVEN data to statistically characterize thermal electron distributions in Mars's magnetotail, revealing how magnetic field topology influences electron density and source regions.

Contribution

It provides the first statistical analysis of thermal electrons in the Martian magnetotail, linking electron populations to magnetic field orientation and crustal magnetic fields.

Findings

Thermal electron densities vary greatly, averaging 20-50 /cc, peaking at 100 /cc outside the optical shadow.

Electrons near Mars are likely from the nightside ionosphere, while those further out originate from the dayside.

Electron observation likelihood increases by 20% when crustal fields point sunward.

Abstract

Thermal (<1 eV) electron density measurements, derived from the Mars Atmosphere and Volatile Evolution's (MAVEN) Langmuir Probe and Waves (LPW) instrument, are analyzed to produce the first statistical study of the thermal electron population in the Martian magnetotail. Coincident measurements of the local magnetic field are used to demonstrate that close to Mars, the thermal electron population is most likely to be observed at a cylindrical distance of ~1.1 Mars radii (RM) from the central tail region during times when the magnetic field flares inward toward the central tail, compared to ~1.3 RM during times when the magnetic field flares outward away from the central tail. Similar patterns are observed further down the magnetotail with greater variability. Thermal electron densities are highly variable throughout the magnetotail; average densities are typically ~20-50 /cc within the optical shadow of Mars and can peak at ~100 /cc just outside of the optical shadow. Standard deviations of 100% are observed for average densities measured throughout the tail. Analysis of the local magnetic field topology suggests that thermal electrons observed within the optical shadow of Mars are likely sourced from the nightside ionosphere, whereas electrons observed just outside of the optical shadow are likely sourced from the dayside ionosphere. Finally, thermal electrons within the optical shadow of Mars are up to 20% more likely to be observed when the strongest crustal magnetic fields point sunward than when they point tailward.