Planetary Plasma Modeling and Ion Escape

Egan, Hilary

Graduate Thesis Or Dissertation

Planetary Plasma Modeling and Ion Escape Público Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/kw52j916p

Abstract

In this thesis I use global plasma simulations to explore the star-planet interaction for Mars and Mars-like exoplanets, with an emphasis on the relationship to ion escape.

I compare the results of five global Martian plasma models run with identical input conditions to each other and corresponding MAVEN data, in order to assess the effect of the different physical assumptions and numerical implementations. I show that no one model outperforms all others in every data comparison, necessitating the careful selection of model for the type of physics one is analyzing. There are clear morphological differences in ion behavior in the tail and southern hemisphere, as well as in the location of various plasma boundaries.

I then apply a hybrid plasma model to the study of a generic Mars-like planet in the habitable zone of a typical M-dwarf star. I systematically vary the stellar input conditions and examine the changing plasma environment and ion escape. Both ion loss morphology and overall rates vary significantly, and in cases where the stellar wind pressure was increased, the ion loss begins to be diffusion or production limited. A quasi-parallel interplanetary magnetic field drives asymmetrically draped field lines and correspondingly asymmetric ion escape.

I use the same hybrid model to explore the effects of intrinsic planetary magnetic field strength on ion outflow, for both current Mars and a Mars-like exoplanet. The presence of an intrinsic magnetic field enhances escape to a certain point before beginning to inhibit it, depending on the polar cone angle and the magnetic standoff distance. I argue that ion escape reflects a balance between the competing effects of magnetic shielding at the equator and enhanced escape at the poles.

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