Cometary Ion Dynamics with Rosetta Ion Composition Analyzer

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Sähkötekniikan korkeakoulu | Master's thesis
Space Robotics and Automation
Degree programme
Erasmus Mundus Space Master
85 + 9
For centuries, comet sightings have fascinated us and we have strived to understand their nature. The knowledge of the behavior and composition of comets would help in understanding the formation of the Solar System, as they are believed to be the oldest objects in it. Cometary research, however, is in a developing stage because from an estimated trillion of comets, we have studied one through extended in-situ in-orbit measurements. Previous research has now established that comets become visible when they approach close to the Sun while their surface volatile material is sublimed by the solar radiation. The neutral atmosphere thus created is also ionized by the solar radiation, resulting in creation of positive cometary ions that are picked up and accelerated by the solar wind electric and magnetic fields. The fields influence the trajectories of these accelerated ions, causing variations in their flow angles as a function of their energy, a mechanism called energy - angle dispersion. Dispersion has only been studied for specific cases so far. In this work, the nature of the energy - angle dispersion is statistically examined using scientific data from the Rosetta mission, which orbited the Comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. One of the instruments onboard Rosetta, the Ion Composition Analyzer (ICA), measured the three-dimensional 360◦ × 90◦ energy and mass distribution of positive ions around the comet. In this work, the ICA data is used to identify dispersion events, their properties and trends using data analysis and image processing techniques at different temporal resolutions. The results are analyzed against the data from physical simulations, models and instruments onboard Rosetta. With the detailed statistical and quantitative analysis of the evolution of the energy - angle dispersion, it is found that the dispersion events are quite coherent over time scales of a few days and that the dispersion is very dynamic in nature. An understanding of this dispersion of accelerated cometary ions is key to understand the cometary ion dynamics.
Kallio, Esa
Thesis advisor
Järvinen, Riku
Rosetta, Ion Composition Analyzer, 67P/C-G, dynamics, dispersion
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