Dissertation
Characterizing global behaviors of precipitating solar wind hydrogen at Mars
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2023
DOI: 10.25820/etd.006982
Abstract
Mars is home to both a collisional CO2 atmosphere and atomic hydrogen corona, which can directly interact with the solar wind. Protons in the solar wind can charge exchange with neutral hydrogen within the corona, resulting in a population of fast, energetic neutral atoms (ENAs). These ENAs bypass electromagnetic boundaries and penetrate to altitudes of ∼120 km. On their path of propagation,ENAs can undergo charge-changing collisions with CO2, resulting in populations of H+ and H−. Utilizing in situ data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we seek to characterize global behaviors of H+ and H−. We find that H+ particles are governed by electromagnetic forces until a given point within the atmosphere, at which point they become dominated by collisional processes. We find that the observed behavior of H+ in magnetized regions disagrees with current models. We demonstrate that H− precipitation occurs under extremely specific conditions and is a function of numerous drivers. We observe most precipitation events during Mars’s dust season during high energy solar wind conditions. When comparing H+ and H− fluxes as a function of atmospheric column density, we find that the peak ratio of their fluxes is ∼8. We also develop a simple modelrepresenting the equilibrium conditions for H−. We find that although photodetachment dominates at altitudes above ∼300 km, it is nonetheless negligible. We compare predictions from a previous model with MAVEN H+ data and find that our observations are in good agreement with this empirical estimate.
Details
- Title: Subtitle
- Characterizing global behaviors of precipitating solar wind hydrogen at Mars
- Creators
- Sarah Henderson
- Contributors
- Jasper Halekas (Advisor)Gina DiBraccio (Committee Member)Allison Jaynes (Committee Member)Vincent Rodgers (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Autumn 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006982
- Number of pages
- xvi, 122 pages
- Copyright
- Copyright 2023 Sarah Henderson
- Language
- English
- Date submitted
- 10/07/2023
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 100-108).
- Public Abstract (ETD)
As we look towards sending humans to Mars, understanding the planet's atmospheric dynamics is key in ensuring the success of future missions. This dissertation seeks to better understand how the solar wind, a fast, hot plasma released from the Sun, interacts with Mars's upper atmosphere. Protons within the solar wind are able to obtain single electrons from a large hydrogen component of the Martian atmosphere, leading to a population of fast, neutral hydrogen atoms. These energetic neutral atoms (ENAs) are able to penetrate to low altitudes within the CO2 dominated portion of the planet's atmosphere. When these hydrogen ENAs interact with CO2, they can lose an electron, gain an electron, or become excited. These three processes lead to H+ particles, H- particles, and proton aurora, respectively. Using data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we examine the behaviors of H+ and H- as a function of various conditions. We characterize the effects that magnetic fields have on H+, determine under what conditions we most often observe H-, compare the behaviors of H+ and H- in different parts of the atmosphere, mathematically determine where these particles reach equilibrium, and compare this mathematical model to observations from MAVEN.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984546542502771
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