1. Pluton's and Charon's diameter for each and total mass are known. How to deduct the mass of Pluton? It could be proportional to their volumes if the density is similar from one to the other.
Pluton represents 7/8 of the total volume. We could thus deduce the mass.
2. The density of Pluton is twice as much as that of the water. People found that Pluton consisted with frozen methane which is very light. So the two findings are contradictory. Which one is true?
3. Density is correlated with the distance from the Sun. Inner planets have higher densities (4-5 times of density of water. consisted by iron and rocks), outer planets have lower density (satellite of je sais pas quoi =2/3 times of water density) => pluton could be lighter, consist majorly by frozen methane.
4. There must be some rocks on the Pluto. Yes, it has 3/4 of rocks and the rests are methane + water.