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Published January 7, 2000 | public
Journal Article

Evidence for Crystalline Water and Ammonia Ices on Pluto's Satellite Charon


Observations have resolved the satellite Charon from its parent planet Pluto, giving separate spectra of the two objects from 1.0 to 2.5 micrometers. The spectrum of Charon is found to be different from that of Pluto, with water ice in crystalline form covering most of the surface of the satellite. In addition, an absorption feature in Charon's spectrum suggests the presence of ammonia ices. Ammonia ice–water ice mixtures have been proposed as the cause of flowlike features observed on the surfaces of many icy satellites. The existence of such ices on Charon may indicate geological activity in the satellite's past.

Additional Information

© 2000 American Association for the Advancement of Science. Received 23 September 1999; accepted 6 December 1999. We thank R. Clark and D. Cruikshank for making their spectral data available to us and E. Young and D. Cruikshank for insightful comments on the manuscript. M.E.B. is an Alfred P. Sloan Research Fellow. These data were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the Universities of California, and NASA. The observatory was made possible by the financial support of the W. M. Keck Foundation.

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