HCN mole fraction profile obtained with the best fit to the data (thick black line). Other possible profiles fitting the data based on the χ² within 1σ noise are shown as the shaded (dark gray) envelope, and the total 1σ uncertainty plotted in light gray. For comparison, we show the profiles of Lellouch et al. (1994) (thick orange) and Marten et al. (2005) (thick green) along with their estimated uncertainties (shaded regions of the respective colors).