  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.

Earth and Planetary Astrophysics;Plasma Physics;Space Physics