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 CO 2 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 CO 2 vibrational temperatures combined with a non‐LTE (local thermal equilibrium) excess of excited CO 2 and/or (b) a non‐Maxwellian electron distribution that moderates CO 2 cooling.