Nordheim, TA; (2016) Charged particle interactions at unmagnetized bodies. Doctoral thesis , UCL (University College London).

Abstract

The overall theme for the work presented in this thesis is charged particle interactions at solar system bodies which do not possess a strong intrinsic magnetic field. This is the case for the planet Venus and minor bodies, such as comets, exposed to the solar wind as well as moons which orbit inside giant planet magnetospheres. In Chapter 2 I investigate surface charging at Saturn’s moon Hyperion, which spends most of its orbit inside Saturn’s strong magnetic field, and is thus exposed to the corotating hot plasma of the Saturnian magnetosphere. This discussion is supported by interpretation of charged particle and magnetic field observations by instruments onboard the Cassini spacecraft as well as by theoretical modelling. In Chapter 3 I extend the work on surface charging to conduct a theoretical study of surface charging effects on the nucleus of comet 67P/Churyumov-Gerasimenko, which is the target of the currently ongoing Rosetta mission operated by the European Space Agency. In Chapter 4 I present an analysis of electron observations made by the Venus Express spacecraft as it carried out a series of maneuvers which took the spacecraft deep within the Venusian ionosphere, to altitudes not previously sampled by a modern plasma instrument. In Chapters 5 and 6 I present the results of modelling of high energy cosmic ray interactions with the Venusian atmosphere, both due to the constant background of Galactic Cosmic Rays (GCR) as well as sporadic Solar Energetic Particle (SEP) events. This includes a study of the possible effects that extreme SEP events, as exemplified by the Carrington event of 1859, may have on atmospheric ionization rates.

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