a New Horizons map of the southeast Cthulhu region on Pluto, located in the equatorial regions west of Sputnik Planitia. Yellow box indicates the boundaries of the area seen in detail in (b). b Detail of the CH4 frost-capped ridges of Pigafetta and Elcano Montes within Cthulhu Macula (148.2°E, 10.1°S), seen in an enhanced Ralph/MVIC colour image (680 m/pixel, cylindrical projection). c Satellite view of water ice-capped mountain chains in the Alps. d LEISA CH4 band depth map focusing on the Pigafetta Montes within Cthulhu, superimposed on the visible map, with blue-to-red indicating increasing CH4 absorption. e CH4 phase index map (at ~3× lower spatial resolution, see definition in ‘Methods’, Phase index maps), with red corresponding to CH4-rich ice and green-blue to N2-rich ice containing CH4. Yellow corresponds to some mixture of both phases. The high value of the CH4-phase index likely indicates that only the CH4-rich phase is present. f Same as (d) for the N2 band depth map. g New Horizons elevation map. Lateral resolution of the topography data at Pigafetta Montes is ~2.5 km, with a vertical precision of 230 m11.