Pluto might still have an ocean underneath its icy shell
 

Thanks to New Horizons, we now know just how complex Pluto's surface is, with its mountain ranges, deep cracks, volcanoes, canyons and heart-shaped plain. Scientists think those tectonic features are the result of a subsurface ocean slowly freezing o...

https://www.engadget.com/2016/06/23/...surface-ocean/