UBC Theses and Dissertations
Mars’ external and internal magnetic fields from orbital observations Mittelholz, Anna
Magnetic fields play a big role in the evolution of a planet and can be used as a tool to understand the interior of it. Orbital spacecraft missions, Mars Global Surveyor (MGS) and Mars Atmosphere and Volatile EvolutioN (MAVEN), have acquired magnetic field data, collectively providing full global coverage at different altitudes. Those data carry information about fields of internal origin, specifically the crustal field, and of external origin, fields generated by the Sun and in the ionized upper atmosphere. Time variable external fields induce electric currents in the subsurface, providing information about the electrical conductivity structure and thus, material properties of the martian interior. The locally strong static crustal field of Mars provides evidence for an ancient global dynamo field. I first explore the global structure of external fields and what we can learn from this, in particular about the contribution of the ionosphere to large-scale magnetic fields. I then investigate how we can extract magnetically quiet orbits, e.g., orbits during which the external field is minimal, from MAVEN data to use in crustal field models. Such models are essential for predicting the field at the surface of the planet and the magnetization responsible for it; this is important for mission planning and we show predictions for the landing sites of Mars 2020 and InSight. Furthermore, such predictions in combination with satellite data provide insight into ancient Mars. I specifically address the timing of the ancient dynamo, and the distribution of magnetization in Mars’ crust. Thus, in this thesis I explore internal and external aspects of the field, contributing to the understanding of past and on-going processes of Mars.
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