Number 104 (Story #1), November 25, 1992 by Phillip F. Schewe and Ben Stein CHARON MAY BE NOTHING BUT ICE . Scientists at the Jet Propulsion Lab have determined from observations made with the Hubble Space Telescope that Pluto's mass is 11 times that of its moon. Previously, the diameters of Pluto (2300 km) and Charon (1190 km) had been worked out from mutual-eclipse measurements. This allows the density of each body to be estimated. Charon, with a density of 1.4 g/cm3, should be mostly water ice. (New Scientist, 21 Nov. 1992.)