Panel a: outgassing rate Q₀ reconstructed from the inversion of the analytical model (black line), compared to the original input outgassing rate (Hansen et al. 2016; blue stars) during the Rosetta mission (2014–2016). The orange line is the result of the simplified approach of Eq. (25) where only He²⁺ →He⁺ reactions were considered (Simon Wedlund et al. 2016); this method works well at the constant solar wind speed of 400 km s⁻¹ chosen here.Panel b: geometry parameters of the spacecraft Rosetta at comet 67P during its two-year mission: black, cometocentric distance; red, heliocentric distance. Two large cometocentric distance excursions are indicated in blue: the dayside excursion (September–October 2015), and the cometary tail excursion (March–April 2016). Gray-shaded regions mark years.