EUROPAS DIFFERENTIATED INTERNAL STRUCTURE - INFERENCES FROM 4 GALILEOENCOUNTERS

Radio Doppler data from four encounters of the Galileo spacecraft with the jovian moon Europa have been used to refine models of Europa's in terior. Europa is most Likely differentiated into a metallic core surr ounded by a rock mantle and a water ice-liquid outer shell, but the da ta cannot eliminate the possibility of a uniform mixture of dense sili cate and metal beneath the water ice-liquid shell. The size of a metal lic core is uncertain because of its unknown composition, but it could be as targe as about 50 percent of Europa's radius. The thickness of Europa's outer shell of water ice-liquid must lie in the range of abou t 80 to 170 kilometers.