IRTF/SpeX observations of Plutos near-infrared reflectance spectrum during 2013 show vibrational absorption features of CO and N$_2$ ices at 1.58 and 2.15 {mu}m, respectively, that are weaker than had been observed during the preceding decade. To reconcile declining volatile ice absorptions with a lack of decline in Plutos atmospheric pressure, we suggest these ices could be getting harder to see because of increasing scattering by small CH$_4$ crystals, rather than because they are disappearing from the observed hemisphere.
تحميل البحث