Spectral slope (% / 1000 Å), calculated between 0.40 and 0.75 μm for spectra of Pluto normalized at 0.60 μm vs. longitudes (top panel), and map of part of the surface of Pluto result of combination of images taken by the Long Range Reconnaissance Imager (LORRI) on New Horizons and combined with the lower-resolution color data from the instrument Ralph on the spacecraft (bottom panel) (http://www.nasa.gov/mission_pages/newhorizons). The scale of the horizontal axis is the same for the top and bottom panels. The red line indicates the sub-Earth latitude at which our data have been obtained (~51°).