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TY - JOUR AU - Buie, Marc W. AU - Cruikshank, Dale P. AU - Lebofsky, Larry A. AU - Tedesco, Edward F. PY - 1987 DA - 1987/10/01 TI - Water frost on Charon JO - Nature SP - 522 EP - 523 VL - 329 IS - 6139 AB - The current series of mutual eclipses between Pluto and its satellite, Charon, provides a very powerful means of probing the most distant known planet in our Solar System. Observations from 1985 and 1986 have already dramatically improved our knowledge of the sizes, albedos, and the orbital parameters of the system1–3. One experiment that we had been waiting to perform is to observe Pluto during a total eclipse of its satellite. This geometry provides a direct means to study the planet without contamination from the satellite. Once the spectrum of the planet is known, it is then possible to subtract it from the spectrum of the planet plus satellite and thus discern the properties of the satellite. Here we present new spectra of the Pluto–Charon system taken just before and during a total eclipse of the satellite. From these data we have extracted the spectrum of the satellite, Charon, which reveals the spectral signature of water ice. There is no evidence for any methane or ammonia frost on the surface of Charon. This observation places important constraints on the composition and origin of this planetary system. SN - 1476-4687 UR - https://doi.org/10.1038/329522a0 DO - 10.1038/329522a0 ID - Buie1987 ER -