Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

Laila Andersson

Second Advisor

Robert E. Ergun

Third Advisor

David Brain

Fourth Advisor

Julie Comerford

Fifth Advisor

Jeffrey Thayer

Abstract

Understanding the formation and evolution of planetary bodies is of great interest and importance to humankind. Mars, being the closest analogue to Earth in our solar system, has been of particular importance. Having studied the red planet for many decades using landers and orbiting spacecraft, we are now laying the groundwork to venture there ourselves. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission recently went into Mars orbit to study the physical processes active within the Martian atmosphere, and to understand how the atmosphere itself has evolved throughout the planet's history. This thesis is based upon unraveling data from the MAVEN mission, with a focus on the structure and energetics of the Martian ionosphere. Data from many of the instruments carried by MAVEN have been analyzed in this work, in particular, analysis and fitting of current-voltage sweeps measured by the Langmuir Probe and Waves instrument. New insights have been gained about the operation of Langmuir probes in planetary ionospheres, and through first author papers, about the Martian ionosphere itself. The four papers presented in this thesis focus on the structure and energetics of the Martian ionosphere. The first in-situ observations of the Martian nightside electron density and temperature showed that an ionization source is needed to sustain the observed densities. Precipitating electrons were shown as a feasible source, agreeing with suggestions from previous modeling efforts. The transfer of energy from the solar wind to the atmosphere is an important energy source for the Martian atmosphere. An investigation of the electromagnetic environment at Mars shows how the distribution of wave power, and various plasma boundaries within the Martian magnetosphere, respond to upstream solar wind conditions, highlighting regions important for energy dissipation. The combination of magnetic field and ion data allows for the first time at Mars, ion conics to be observed. These show evidence of parallel acceleration and ion heating present at low altitudes in the ionosphere. Finally, an investigation of sporadic disturbances observed below the Martian exobase showed that the Rayleigh-Taylor instability is present in the Martian ionosphere. Similar disturbances are present in the terrestrial ionosphere and are known as Equatorial Spread F (ESF). Such disturbances cause communication problems within the terrestrial ionosphere and similar problems may occur when humans reach the surface of the red planet.

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