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Solar wind charge-changing reactions are of paramount importance to thephysico-chemistry of the atmosphere of a comet because they mass-load the solarwind through an effective conversion of fast, light solar wind ions into slow,heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko(67P) provided a unique opportunity to study charge-changing processes in situ.An extended analytical formalism describing solar wind charge-changingprocesses at comets along solar wind streamlines is presented. It is based on athorough book-keeping of available charge-changing cross sections of hydrogenand helium particles in a water gas. After presenting a general 1D solution ofcharge exchange at comets, we study the theoretical dependence of charge-statedistributions of (He$^{2+}$, He$^+$, He$^0$) and (H$^+$, H$^0$, H$^-$) on solarwind parameters at comet 67P. We show that double charge exchange for theHe$^{2+}$-H$_2$O system plays an important role below a solar wind bulk speedof 200 km/s , resulting in the production of He energetic neutral atoms,whereas stripping reactions can in general be neglected. Retrievals ofoutgassing rates and solar wind upstream fluxes from local Rosetta measurementsdeep in the coma are discussed. Solar wind ion temperature effects at 400 km/ssolar wind speed are well contained during the Rosetta mission. As the cometapproaches perihelion, the model predicts a sharp decrease of solar wind ionfluxes by almost one order of magnitude at the location of Rosetta, forming ineffect a solar wind ion cavity. This study is the second part of a series ofthree on solar wind charge-exchange and ionization processes at comets, with aspecific application to comet 67P and the Rosetta mission.

Solar wind charge exchange in cometary atmospheres. II. Analytical model