Dimensionless parameter 2αn_i(r)r∕U_n (Eq. (27)) as a function of Q∕Q₀ (Q₀ defined by Eq. (20)). The ion number density n_i is derived from Cravens (1987; red solid line, Eq. (31)), Galand et al. (2016; Eq. (29)) assuming r = 1.1 r_c (dotted blue line), r = 2 r_c (dashed blueline), and r ≫ r_c (solid blue line, Eq. (30)), Gombosi (2015) or this work assuming r ≫ r_c (black circles, Eq. (28)), and this work assuming r = 1.1 r_c (blue upward-pointing triangles, ▴), r = 2 r_c (orange downward-pointing triangles, ▾). Photoabsorption is ignored here. Conditions at 1P during the Giotto encounter and at 67P during the Rosetta escort phase are overplotted as gray areas. We provide a broad range of values for 1P as uncertainties remained on the electron temperature and therefore on the e⁻ -ion dissociative recombination rate, which depends on the electron temperature. This last was assumed to be between 150 K (upper bound) and 1000 K (lower bound; see Table 2). For 67P, the dynamic range of Q∕Q₀ is primarily driven by the outgassing rate Q, from 10²⁵ (end of mission) to 6 × 10²⁸ s⁻¹(perihelion), and the heliocentric distance, which affects the photoionization frequency.