In‐Situ Measurements of Electron Temperature and Density in Mars' Dayside Ionosphere. Issue 14 (23rd July 2021)

• Record Type: Journal Article
• Authors: Ergun, R. E.; Andersson, L. A.; Fowler, C. M.; Thaller, S. A.; Yelle, R. V.
• Is Part Of: Geophysical research letters. Volume 48:Issue 14(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-23
• Subjects: electron temperature -- Mars' ionosphere -- CO2 temperatures -- CO2 excited states -- energy transfer; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL093623
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. Plain Language Summary: The MAVEN satellite has measured electron temperatures with sufficient accuracy to test atmospheric and ionospheric models at Mars. The measured electron temperatures are found to be significantly higher than most models predict, which indicates that the electron‐CO2 energy exchange may not be fully understood or that an unidentified energy source is heating electrons. This article proposes that the elevated electron temperatures may be due to a high abundance of CO2 in an excited state. The implication is that the electron temperature may be an indication of the excitement of CO2 rather than its thermal (kinetic) temperature. Key Points: In‐situ measurements of the electron temperature and density in Mars' dayside ionosphere Electron temperatures are higher than predicted at low altitudes in Mars' ionosphere Modeling electron temperatures require evaluation of electron‐CO2 vibrational excitement/de‐excitement and electron distributions