Aikaterini Stergiopoulou: The induced magnetospheres and magnetotails of Mars and Venus

Abstract

In this work we focus on several aspects of the ionospheres, induced magnetospheres, and magnetotails of the unmagnetized planets Mars and Venus. The solar wind interaction with unmagnetized planets differs from the magnetized planets: they are more directly exposed to the solar wind, and consequently can respond faster and more dynamically to solar wind variations, necessitating careful analysis of the driving conditions upstream simultaneously with plasma measurements in the system. This thesis is a compilation of an introductory part, and four articles. Three examine the ionosphere and the induced magnetosphere of Mars, while the last one investigates the properties of the induced magnetotail of Venus. Data from ESA’s Mars Express (MEX) and NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) missions are used in the Mars studies, while measurements from the two first Venus flybys of ESA’s Solar Orbiter (SolO) mission are used in the final paper. In our first study we investigate the nightside ionosphere of Mars using measurements from special high altitude operations of the ionospheric radar on board MEX. We find a consistent presence of plasma in the terminator region and we observe for the first time escaping plasma structures at solar zenith angles (SZAs) up to ~180 degrees at these high altitudes. The second project is a two-spacecraft statistical study where we use truly simultaneous observations from MEX in the induced magnetosphere of Mars and from MAVEN in the solar wind. Our aim was to investigate the response of the Martian induced magnetosphere to upstream conditions, and we find that even though stronger magnetic fields are observed in the induced magnetosphere for intervals of high solar wind dynamic pressure, when we compare these fields with the IMF magnitude the resulting ratio is actually enhanced during low pressure intervals, indicating the “volume” of the solar wind interacting with Mars is in fact larger in this situation. In the third study we investigate the correlation between electron densities and temperatures with crustal fields, and show the influence of the solar wind and IMF on this relationship. Finally, in our last study we observe the distant induced magnetotail of Venus, a region not well explored, through electron density and magnetic field observations from the first two SolO Venus flybys and compare with a global hybrid simulation. Together, this thesis expands our understanding of the plasma structures and dynamics of induced magnetospheres and magnetotails, using unique spacecraft data sets.