Low Electron Temperatures Observed at Mars by MAVEN on Dayside Crustal Magnetic Field Lines

Abstract

The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. The current paper studies electron temperatures in the dayside for two regions where (1) crustal magnetic fields are dominant and (2) draped magnetic fields are dominant. Overall, the electron temperature is lower in the crustal‐field regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet conditions, which is associated with the local extreme ultraviolet energy deposition. The current models underestimate the electron temperature above 250‐km altitude in the crustal‐field region. Electron heat conduction associated with a photoelectron transport in the crustal‐field regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron's upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustal‐field region should be considered for future numerical simulations.

Subsolar Electron Temperatures in the Lower Martian Ionosphere

“…The electron temperature altitude profiles are consistent with previous results reported from the MAVEN/LPW instrument during normal, that is, nondeep dip operations (e.g., Fowler, Andersson, Ergun, et al, ; Fowler, Andersson, Peterson, et al, ; Peterson et al, ). The electron temperatures below ~200 km were also shown to be independent of magnetic field orientation, consistent with the results of Sakai et al ().…”

“…The Andersson electron temperature spike feature, an unexpected increase in electron temperatures over a narrow altitude range at low subsolar altitudes first described by Andersson et al (), is seen in the median values (Figures b, d, and f) near 152 km in DD2 and 132 km in DD8 and DD9. No systematic difference in the electron temperature profile as a function of dip angle is seen below 250 km, consistent with the results of Sakai et al () obtained from a much larger data sample. Measured ion temperatures from the Supra Thermal and Thermal Ion Composition instrument (McFadden et al, ) are not reported in Figure because algorithms to account for all instrumental effects encountered at thermal energies are not yet available.…”

In‐Situ Measurements of Electron Temperature and Density in Mars' Dayside Ionosphere

“…The recalibrated data show that the measured T e altitude profiles have meaningful differences from several ionospheric models (e.g., Choi et al., 1998; Matta et al., 2014; Sakai et al., 2016, 2019; Vigren & Cui, 2019). In particular, the measured values of T e are higher than the modeled values at the lowest altitudes.…”

“…The electron temperature (T e ) and density (n e ) are fundamental parameters in each of the steps. At the lowest altitudes in the ionosphere, T e can influence a number of photochemical interactions (Alge et al,1983;Barth, 1985;Brecht et al, 2017;Sakai et al, 2019). At the top side of the ionosphere, the ambipolar electric field that results from T e can energize ions near the exobase and substantially increase ion loss (Brecht et al, 2017;Ergun et al, 2016Ergun et al, ).…”

Kinetic Modeling of Langmuir Probes in Space and Application to the MAVEN Langmuir Probe and Waves Instrument

“…To fully understand the ion loss process, one must model the photo‐chemical processes in Mars' ionosphere, several of which depend on the electron temperature ( T e ) and density ( n e ) (e.g. Alge et al., 1983; Barth, 1985; Brecht et al., 2017; Ergun et al., 2016; Sakai et al., 2019).…”