Electron cooling in a cometary coma

University essay from Uppsala universitet/Institutionen för fysik och astronomi

Author: Simon Alinder; [2017]

Keywords: Comet; Plasma; Inner coma;

Abstract: The ESA Rosetta spacecraft investigated comet 67P/Churyumov-Gerasimenko duringtwo years from August 2014 to the end of September 2016. The dual Langmuir probewas used to measure plasma parameters including the thermal energy of theelectrons. The observed thermal energy (or temperature) of the electrons was ratherhigh, in the range 5-10 eV almost throughout the mission. However, near perihelionthe Langmuir probe measurements indicated the prevalence of two electronpopulations with distinct temperatures, one hot (5-10 eV) and one cold (less than 1eV). It has been hypothesized that the electrons of the colder population wereformed relatively close to the nucleus and that they subsequently cooled by inelasticcollisions with the neutral gas. In this project work we develop a model for studyingelectron cooling in a cometary coma. The model takes into account collisions withwater molecules as well as the influence of a radial ambipolar electric field.

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