Interpreting an unexpected and unexplained signal measured at comet 67P by the ion mass spectrometer RPC-ICA

Sammanfattning

Comets are among the oldest residents of our solar system, making them a valuable source of information about the origins of our part of the universe. The Rosetta mission launched in 2004 heading for comet 67P/Churyumov-Gerasimenko to be the first spacecraft to closely follow a comet. Aboard the spacecraft was the Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA), with the objective of measuring cometary as well as solar wind ions. During 2016, the final year of the Rosetta mission, a strange signal appeared in the RPC-ICA data. Energy-time spectrograms of incoming particles started to display an unexpected shape. The signal had similarities to a signal in the Rosetta Ion and Electron Sensor (RPC-IES) interpreted as due to negatively charged nano-dust. Could this perhaps be something similar for positively charged dust? In this thesis the strange signal is analysed in an attempt to identify its origin. Data from the instrument were plotted with respect to time, energy, mass, and instrument field of view. The occurrences of the strange signal were put in the perspective of the surrounding cometary environment and its changing nature. In an attempt to recreate the strange signal, ion optics simulations were performed. Results suggest that while the instrument functions as it should in terms of measuring solar wind and cometary ions, the strange signal was caused by particles moving through the instrument on a non-nominal path. The cometary environment was also found to play a role in the creation of the signal.