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Observations Show Frigid Charon Has Had Some Hot Times<br />By Greg Clark<br />Staff Writer<br />posted: 02:05 pm ET<br />30 December 1999<br /><br />The rare alignment of Pluto, its moon Charon and exceptional viewing conditions from the Keck Telescope has startled scientists with evidence that the surface of the planet's chummy satellite has been much warmer than anyone had imagined.<br /><br />The discovery turned up on a night last May when planetary scientist Michael Brown, of the California Institute of Technology, and some colleagues were observing something completely different. "When we realized what a spectacular and unusual night we had, we scrapped our complete plans," and turned the telescope toward Pluto, Brown said.<br /><br />The desire to get good observations of Pluto and its only known moon had been in the back of his mind for a while, so Brown seized the opportunity afforded by near-perfect viewing conditions on top of Hawaii's 14,000-foot Mauna Kea volcano. The result was unprecedented quality and sharpness in measurements of Pluto's and Charon's spectra.<br /><br />In the 21 years since Charon was discovered, attempts to analyze its composition have always been complicated by the moon's proximity to Pluto. The two bodies are so close together (barely more than 12,000 miles, or 19,500 kilometers apart) and so far away from Earth (more than 30 times farther from the sun than Earth), that it has been difficult to make separate measurements of the two.<br /><br />With the Keck observations, though, Brown was able to distinctly resolve the two and measure the spectral signature of Charon itself. He found that Charon -- which is composed predominantly of water ice at the surface -- is made of a form of ice that shouldn't exist at the frigid minus 370 degrees Fahrenheit (minus 225 Celsius) that is thought to be the hottest temperature the moon ever reaches.<br /><br />The ice appears to be in a crystalline form: its molecules are neatly ordered and arranged into the <div class="Discussion_UserSignature"> </div>