The 5 January issue of Nature reports findings by astronomers from MIT and the Paris Observatory that add to the little that we know about Charon, Pluto's 'moon', as it is commonly referred to (although its status as a moon is disputed by some).
Using the event of Charon occluding (blocking) a distant star, the astronomers were able to determine several things about Charon. When Charon passed in front of the star, the light was immediately blocked, which implies the absence of a significant atmosphere (else it would have faded out more gradually). By observing the occlusion from two locations, they were able to tell its diameter. Then, by combining knowledge of its size with prior estimates of its mass, they were able to estimate its density and further, its composition (60% rock and 40% ice). Now that is an impressive amount of logical deduction from what amounts to using a stop watch to time a blinking (star) light.
Both teams of astronomers posted video (Paris and MIT). Be careful on the MIT clip as it crashed both Firefox (1.5) and IE for me.
Hat tip ScienceNOW Daily News.
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