The distribution of H2O, CH3OH, and hydrocarbon-ices on Pluto: Analysis of New Horizons spectral images

International audienceOn July 14, 2015, the New Horizons spacecraft made its closest approach to Pluto at about 12,000 km from its surface (Stern et al., 2015). Using the LEISA (Linear Etalon Imaging Spectral Array) near-IR imaging spectrometer we obtained two scans across the encounter hemisphere of Pluto at 6-7 km/pixel resolution. By correlating each spectrum with a crystalline H2O-ice model, we find several sites on Pluto's surface that exhibit the 1.5, 1.65 and 2.0 µm absorption bands characteristic of H2O-ice in the crystalline phase. These sites tend to be isolated and small ( 2.3 µm. Such heavy hydrocarbons are much less volatile than N2, CH4, and CO at Pluto temperatures. We test for CH3OH, C2H6 , C2H4 , and C3H8-ices because they have known optical constants and these ices are likely to arise from UV and energetic particle bombardment of the N2, CH4, CO-rich surface and atmosphere. Finally, we attempt to estimate the surface temperature using optical constants of pure CH4 , and H2O-ice and best-fit Hapke models. Our standard model gives temperature estimates between 40 and 90 K, while our models including amorphous H2O-ice give lower temperature estimates between 30 and 65 K