Haze optical depth (multiplied by 10³), compared to imaginary refractive indices of several plausible icy compounds at relevant temperatures. The solid thick line with 2-σ error bars corresponds to the haze optical depth inferred by using the CH₄ seasonal surface temperature model. The thin solid line, which diverges from the previous one longward of 15 μm, makes use of the diurnal-only surface temperature model. References are Moore et al. (2010) for HCN, Ugelow & Anderson (2022) for HC₃N, Hudson & Yarnall (2022) for C₆H₆ and Khanna et al. (1988) for C₄H₂. Also shown are the imaginary refractive indices of Titan’s haze (Vinatier et al. 2012) and of Titan’s tholin analogues (Imanaka et al. 2012). The retrieved haze optical depth is unreliable shortwards of ~13 μm (thin dashed line).