Determining the Relation Between Electron-Neutral Collisions and Thermal Electron Temperature Profiles in the Mars Ionosphere

Abstract

The thermal electron temperature, Te, is an important quantity in planetary ionospheres because many photochemical reaction rates depend on it. Te thus plays a role in driving ion composition, structure and dynamics. In addition, enhancements in Te with altitude have been shown to drive ambi-polar electric fields that can energize cold planetary ions and lead to ion escape to space.The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission acquires Te profiles on each orbit and as a result, a comprehensive data set exists that spans the full range of Mars local times, latitudes and solar zenith angles, allowing us to determine which physical processes control the Te profile shapes and temperature values. We focus on the “transition region,” where Te values can rapidly increase from small values (<500 K) at lower altitudes, to larger values (>1000 K), over a relatively narrow altitude range. The suite of plasma instruments carried by MAVEN allows us to investigate the role of, for example, electron-neutral collisions, ion temperature, wave heating, etc. This study focuses on the effect of electron-neutral collisions on the location and width of the Te transition region. We utilize observations of the neutral atmosphere made by MAVEN’s Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument to calculate electron–neutral collision frequencies, which are compared to measured Te profiles. The calculated collision frequencies provide insight on when collisional processes dominate (over transport and electromagnetic waves, for example), and allow us to identify trends between driving processes and the shape and location of the Te transition region. Understanding the physical processes that control the form of Te profiles will inform us of the mechanisms key to structuring the current day Mars ionosphere. Such understanding will also provide key insight needed for studies of ionospheric escape to space and long-term evolution of the Martian atmosphere.