Measured thermodynamic temperature for the three Planck HFI observations of Mars. Black points represent band averages and corresponding error estimates. The thermodynamic temperature predictions of the Lellouch & Amri (2008) model (solid lines), scaled by ζ_P = 0.982, and the corresponding 5% absolute errors (coloured regions) are also shown. Both data and model results presented in this figure have been scaled to correspond to a single reference time (see discussion in Sect. 3.1). The grey region is meant to remind the reader that the sub-mm bands are calibrated on models of Uranus and Neptune brightness (see Sect. 2.1.2). The absolute thermodynamic temperature of Mars can be obtained by adding the spectral radiance from an occulted CMB monopole (see Sect. 2.1.3).