Evolution of oxygen species after a cometary impact. Initial conditions correspond to deposition of CO and H₂O with uniform mixing ratios (with q_CO = 10 q_H2O) above 300 km. Left panel: models suited to the Herschel H₂O profile (S_a from Moreno et al. (2012)). Dashed lines: “small comet” (initial q_CO = 6 × 10^-5), evolution time t_evol = 300 yr. Solid lines: “large comet” (initial q_CO = 6 × 10^-4), evolution time t_evol = 700 yr. The red circles and black squares show the H₂O and CO₂ for the combination of the “large comet” case with a steady OH influx of 2.4 × 10⁵ cm^-2 s^-1. Right panel: models suited to the Cassini/CIRS H₂O profile Cottini et al. (2012). Dashed lines: “smaller comet” (initial q_CO = 3 × 10^-5), evolution time t_evol = 225 yr. Solid lines: “large comet” (initial q_CO = 6 × 10^-4), evolution time t_evol = 700 yr. The red circles and black squares show the H₂O and CO₂ for the combination of the “large comet” case with a steady OH influx of 9.0 × 10⁵ cm^-2 s^-1. Upper limits on H₂O thermospheric abundance by Cui et al. (2009) are also shown as arrows.