Ion density profiles of a few ions as a function of the cometocentric distance under different conditions: December 2014 (Q = 7.5 × 10²⁵ s⁻¹, 2.75 au, top panel), end of August 2015 (Q = 5 × 10²⁸ s⁻¹, 1.24 au, middle panel), end of January 2016 (Q = 2.4 × 10²⁷ s⁻¹, 2.2 au, bottom panel). We have used the same neutral composition for each case: 88.7% H₂ O, 10% CO₂, 1% NH₃, 0.3% CH₄. The photo-ionisation frequencies ν_p are taken from Huebner & Mukherjee (2015) at low solar activity at 1 au and scaled with respect to the heliocentric distance. The expanding speed of the gas is set to a constant U = 900 m s⁻¹ and the nucleus’ radius r_c to 2 km. Ions are produced from photo-ionisation or photo-dissociative ionisation of the neutral molecules(see Appendix B). The gas temperature is assumed constant at T = 100 K. The grey areas correspond to the cometocentric distance of Rosetta during these periods. The uncertainties from the kinetic rateson the ion number density are represented through coloured shades.