The influence of magnetic field topology and orientation on the 1
distribution of thermal electrons in the Martian magnetotail 2
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.