Creation and distribution of cold plasma in gas giants’ magnetospheres through in situ and remote observations

Xystouris, Georgios and Arridge, Chris and Badman, Sarah (2024) Creation and distribution of cold plasma in gas giants’ magnetospheres through in situ and remote observations. PhD thesis, Lancaster University.

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Abstract

This thesis focused on studying the production and distribution of neutrals and plasma in the magnetospheres of Saturn and Uranus, using data from several instruments that provided both in-situ and remote observations. These specific planets were selected because they are expected to have similarly cold and water-like plasma: Saturn has Enceladus as the main neutral provider, and Uranus has its 5 biggest moons: Ariel, Umbriel, Titania, Oberon and Miranda. While the existence of a water-group plasma is studied thoroughly for Saturn with the Cassini Mission, it is still a topic of debate for Uranus, as no heavy ion plasma was observed during Voyager 2 flyby. For Uranus I searched for the existence of a water neutral torus using observations from Herschel/HIFI. Although models predict such a torus, the data were inconclusive: there was a feature on the data hinting at the existence of a torus, but it was not potent enough to confirm without further study. For Saturn I focused on the factors affecting the cold plasma measurements, particularly the photoelectrons, as they have the same properties as the cold electron plasma. I studied how data from the Cassini/LP and CAPS evolve when Cassini goes into Saturn’s shadow, where the photoelectron generation stops, and I found that data from both instruments exhibited clear changes. Moreover, I calculated the transparency of the main rings based on photoelectrons variations when Cassini was in the rings’ shadow. Lastly, as the sunlight or the plasma flow can be important to an instruments’ measurements, I developed algorithms that use a spacecraft 3D model to: (i) calculate the field-of-view of an instrument mounted on a spacecraft, and (ii) search for any intersections of a vector with any part of a spacecraft. This work can be adapted to any spacecraft.