ROSINA measurements of argon, water, and carbon dioxide at comet 67P. The top row shows the argon densities measured at the location of Rosetta modified by the cometocentric distance squared on the y-axis (modified density). Panel a shows the modified CO₂ density on the x-axis, multiplied by a fitted correlation factor (6.2 × 10⁻⁵) by which the CO₂ density can be multiplied to obtain the measured argon density within 71% accuracy (1−σ corresponding to a multiplication and division by the 1.71 Stdev factor). Panel b shows the same for H₂O and panel c for a linear combination of H₂O and CO₂. Panels d–f show the reconstructed densities based on these correlation factors for the three time periods investigated (cf. Balsiger et al. 2015; Rubin et al. 2018). For more details see the main text.