Thermodynamic temperature of Saturn’s disc as calculated from the four Planck-HFI observations compared with the ESA2 model output. The LFI data at 28, 44, and 70  GHz are taken from Planck Collaboration V (2014), but corrected for disc oblateness and ring contributions. The three prominent absorption lines, including the one at 530 GHz, are phosphine (PH₃) related (Weisstein 1996). Emission lines are due to stratospheric emission from H₂O. WMAP and ACT measurements are included here for comparison (Bennett et al. 2013; Hasselfield et al. 2013; Louis et al. 2014).