spacetoday.net: Astronomers measure size of Charon

Posted: Mon, Jan 9, 2006, 5:32 AM ET (1032 GMT)
Pluto-Charon illustration (CfA)

Astronomers announced last week that they used a stellar occultation to measure the size of Charon, Pluto's largest moon, and confirm that the world does not have an atmosphere. Several teams of astronomers in South America observed Charon as it passed in front of a distant star on July 10, 2005, temporarily blocking the light from the star. Analysis of those observations found that the moon has a radius of 606 kilometers, with a margin of error of only eight kilometers. The lightcurve from the occultation also led researchers to put an upper limit of one microbar on the surface pressure of any atmosphere, consistent with expectations that the moon did not have any substantial atmosphere. The results add additional credence to the hypothesis that the Pluto-Charon system formed through the collision early in the history of the solar system. The results were published in the January 5 issue of the journal Nature.