It's probable just a big rock, like a large moon, however it's too far away to say for sure. A satellite was launched from the Earth and it will fly past Pluto many years from now. Then we should learn a lot more about Pluto.
Pluto is the combination of dust and gases.
Liquid.
gas
a gas and a liquid cause it can be both
solid
solid.
Gas
solild
It is a rare solid.
soild
solid
Soild