Top panel: measured band shifts (Å), with respect to the position of the pure methane from this work vs. Pluto’s longitude. We connected the points corresponding to the bands at 0.73, 0.87, and 0.89 μm with lines to illustrate the variation with longitude (for the other bands, there are too few points). At longitudes between 100° and 200°, the shifts are greater, thus the CH₄:N₂ is smaller, which is compatible with a lower abundance of CH₄ suggested by the smaller band depths shown in Fig. 8. Bottom panel: variation in the shifts (Å) of the bands at 0.89, 1.16, 1.72, and 2.20 μm with respect to the position of the pure methane, from G13. The points in the gray shadow represent replicate values (at longitude ±360°) to better visualize the variation in the band depth with the longitude.