Pluto's a dog. How can a dog have underground oceans?
Silly scientists.
Pluto may contain a colossal underground ocean, say New Horizons mission scientists. Two new Letters in Nature, Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto and Reorientation and faulting of Pluto due to volatile loading within Sputnik Planitia considers the icy heart-shaped “lava lamp” found on the …
"Pluto may contain a colossal underground ocean"
It seems very unlikely that Pluto still has an underground ocean but it may well have had one a few billions years ago when the Sputnik Planitia was formed.
The assertion that there are two reasons why Pluto could currently have a liquid underground ocean is flawed. Firstly, tectonic activity is a consequence of internal heat, not a cause of it, and secondly, Pluto is so small that after ~4 billion years there will be hardly any radioactivity left.
Hold on, this is not an assertion but one of two different theories that have been offered to explain the observed data from New Horizons.
Your observations about the conditions on Pluto may indeed be correct, but there is evidence of the movement of the Sputnik Planitia within recent geological timescales. That and the visual absence of cratering on the surface of the Planitia, which is accepted as evidence of the activity of some sort of process that has recently (geologically speaking again) reshaped the area, leaving a smooth surface.
Some sort of activity is happening out there, that is apparent, and that implies a source of energy to drive it. This is just an attempt to explain that, not proof.
Two possibilities:
1)The impact that cause Sputnik Planitia created the heat required to cause the effects we now observe.
2) The impact crater looks as if the impact may have been slow - this may have been a moon whose eccentric orbit caused heating of Pluto before impact
Half life of Uranium is 3.8 billion years, half life of Thorium is 13 billion years, however, these are
TERRESTIAL EARTH ARTIFACTS, and vary with temperature, pressure and particle bombardment.
Bridgemann Effect, under 100 atmospheres, with Hydrogen, every metallic element is radioactive.
Although Pluto and Charon are tidally locked and Charon's orbit is pretty circular could the fact that the barycenter lies outside of Pluto cause a form of tidal heating since the gravitational pull of Charon will vary as they both orbit around the barycenter or would the effect be much too small ?
The most important point is that Pluto is phase locked to Charon; i.e. Pluto always presents the same face to Charon. For that to happen, there must be body tides in Pluto. How much heating they cause is another matter.
I'd be tempted to say the heating would be greater if the barycentre was inside Pluto, and Charon's orbit was more eccentric and less coplanar. But maybe Charon's mass (12% of Pluto's) more than makes up for that.