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

We present dayside electron temperature (T_e) and density altitude profiles at Mars from MAVEN satellite deep-dip orbits. The data are after recalibration of the Langmuir Probe and Waves instrument that results in reduced uncertainties to as low as ±82°K. At MAVEN's lowest altitudes, (∼120-∼135 km), the measured values of T_e are, after uncertainties, higher than those predicted by several modeling efforts. To better understand this discrepancy, we perform a basic heat-transfer analysis for two specific dayside deep dips. The analysis supports that CO₂ excitation/de-excitation of its lowest-energy vibrational states dominates energy transfer to and from electrons. We hypothesize that the discrepancy between the measured and modeled T_e is due to (a) the coupling of T_e to CO₂ vibrational temperatures combined with a non-LTE (local thermal equilibrium) excess of excited CO₂ and/or (b) a non-Maxwellian electron distribution that moderates CO₂ cooling.