Subaru infrared spectroscopy of the Pluto-Charon system

We present the results of the near-infrared spectroscopy of the Pluto-Charo n system, conducted in the K band at two different sub-Earth longitudes. Th e spatially resolved images resulted in separated spectra with a spectral r esolution of approximately 530. The spectrum of Charon show-ed a broad abso rption feature at 2 mu m during both orbital phases, suggesting a uniform d istribution of water ice. In the separated spectrum of Pluto obtained in Ju ne, we confirmed the absorption bands of solid methane, carbon monoxide, an d nitrogen ices. Additional weak dips have been found at 2.28, 2.32, and 2. 40 mu m in the spectrum of the opposite side observed in May. In order to e xamine the carrier of these dips, we performed model calculations of the re flectance of Pluto using Hapke's bidirectional reflectance model for icy in timate mixtures. By adding a small amount of solid ethane into the mixture, we successfully reproduced the dips at 2.28 and 2.315 mu m, but the absorp tion at 2.40 mu m is more distinct than that in the observed spectrum.