Tides pushing all the ice around!!
The two lobes of the feature are geologically distinct. The western lobe, Sputnik Planum, is smoother than the eastern, and they are of slightly different colors.[10]
Early speculation was that the western lobe may be a large impact crater filled with nitrogen snow. Bright spots within the region were initially speculated to be mountain peaks.[11]
Photos, released on 15 July 2015, revealed 3,400 m (11,000 ft) mountains made of water ice in the feature; they also revealed no craters in this same region, suggesting that the 'heart' is less than 100 million years old and thus that Pluto is probably geologically active.[12]"
OK, I actually hadn't known Pluto was largely covered in ice, or that it had an atmosphere, although a very thin one. In any case, the volcanism created by tidal forces on those moons I referred to around other planets all involved giant/massive planets like Jupiter and Saturn and their moons. I doubt the tidal forces between Pluto and Charon would create much if any frictional heat.