Column densities from the DSMC model compared to VIRTIS-H column densities. A): model results (red) and measurements (black) are plotted as a function of time. B): model as a function of measurements, with the same color coding as in Fig. 7, corresponding to regions in P1. Modeled columns have been multiplied by a factor 0.8 to approximate the column density of H₂O. The markers for the model are at the average point between the values found at the start and stop time of a given observation, which themselves give the error bars. The error bars for VIRTIS-H measurements are shown in Fig. 6.