Liquids may have existed on the surface of Pluto in the past.

We really just didn't realize the diversity of planetary types in our solar system. Pluto looked like a misfit because it was the only one we saw. And just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies. They're large enough to make themselves round by self gravity, and they surely pass the test of planethood.

I tell public audiences, don't go to a podiatrist for brain surgery; don't go to an astronomer for planetary science.

Alan Stern Quotes