Callisto, the outermost of the Galilean satellites (see JUPITER: SATELLITES), is approximately 38% larger in diameter than Earth's Moon (Callisto's radius is 2410 km and the radius of the Moon is 1738 km). However, Callisto's lower mass, surface gravity and higher albedo reflect its ice–rock composition. Callisto's surface is thought to consist of a mixture of ice and dust or rocky materials