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 degrees K. At MAVEN's lowest altitudes, (similar to 120-similar to 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.