The researchers believe that not only was Pluto hot, but it formed quickly. If Pluto formed slowly the surface can cool off before the next impact. However if Pluto formed quickly you have impact on top of impact, repeatedly warming the surface until you get warm enough that an ocean can form. We calculate that Pluto would have had to form in less than about 30,000 years for this to form an ocean." Regardless of how Pluto formed, today its ocean is maintained by the heat of radioactive decay at the dwarf planet's rocky core and the thick ice shell insulates the ocean beneath, Bierson said.

Source: Daily Sun June 22, 2020 18:11 UTC