Mole fraction of O₂ in accreted ice vs the W/R ratio assumed in the parent body. The plots show, for a given W/R, how much accreted O₂ is necessary to oxidize enough of the total sulfur content into a quantity of sulfates consistent with contemporary measurements (see last two columns of Table 1: 16% for the CM case, 39% for the CIcase). The green part of the diagram covers the estimated range of W/R in CM parent bodies, the blue part covers the estimated W/R for CI parent bodies. The CV curve corresponds to the quantity of O₂ that would lead to the oxidation of 1% of sulfur into sulfates. The red overlay represents the range of O₂ abundance in the ice of comet 67P/C-G (3.1 ± 1.1%) as observed by the Rosetta mission (Rubin et al. 2019).