Evolution of the cometary ionospheric sourcing of 67P throughout Rosetta escort phase

International audienceThe Rosetta spacecraft escorted comet 67P from August 2014 to September 2016. During this period, we were able to study the variability of the cometary environment with respect to different parameters such as heliocentric distance, seasonal variations or solar activity. As comets approach the Sun, the surface of the nucleus partially sublimates into a cometary gas. Some of this gas is then ionized through different processes (photon impact, energetic electron impact or solar wind proton impact). We modelled these processes and predicted the local number density of electrons (or ions, by quasi-neutrality of the environment) that would be sampled by the spacecraft. With this methodology we were able to explain the data harvested by the Rosetta instruments and disentangle their different sources. At low heliocentric distances, photo-ionization is the main ionizing process. At high heliocentric distances, we find that photo-ionization and electron-impact ionization are both significant sources. However photo-ionization is very sensible to seasonal variations and solar activity. As the mission progressed, the solar activity decreased therefore the relative importance of electron-impact increased