Fig. 6: Comparison between observed spectrophotometric indexes and modeled values.

a b–x slope value versus normalized photon dose. b 0.7-µm band absorption versus normalized photon dose. c b–x slope value versus peak temperature at perihelion. d 0.7-µm band absorption versus peak temperature at perihelion. The north polar observation (Fig. 1a) and the south pole observation (Fig. 1c) are shown with black and cyan markers, respectively. Observed spectrophotometric indexes are binned by every 0.1 for photon dose and every 10 K for peak temperature. Error bars indicate the standard deviation in each bin. Relative exposure time for a, b is calculated such that the most irradiated surface is defined as unity. Image ids used for this figure are listed in Supplementary Table 1.