Illustration showing the core, mantle and crust of Pluto. Observations by the Hubble space telescope suggest that the internal composition of Pluto consists of roughly 50??0 percent rock and 30??0 percent ice by mass. The diameter of rocky the core is thought to be about 70% of Pluto's diameter. This is surrounded by a thick mantle of ices, and topped with a crust made of ice also, including nitrogen, methane and carbon monoxide.