The Icy Core Model
The gasses (red melon) that make up Pluto's globe are locked in solid and fluid form but given the right conditions or energy and they will return to their gas state and produce an atmosphere and even jettison off into space.
The vacuum of space is attempting to pull the elements and compounds apart but the cold is constricting them together.
Think of Pluto as a watermelon. Put that watermelon in the freezer cool it to 40 degrees above absolute zero making it rock hard then expand it to the size of Charon and Pluto and you have a relatively good analogy for my icy core model.
The watermelon has a thick rind the equivalent of Pluto/Charon's mantle.
The (red melon) gasses that want to escape are trapped and frozen inside if this watermelon had seeds they would be indicative of pockets of various materials.
When impacts occur shock waves fracture the rind and soften the frozen core.
Depending on the intensity of the impact the outward manifestations will vary.
Or perhaps the interior densities of Pluto follows this red cabbage spiral graph shape.
Uniform or Differentiated
This is an image from NASA, they are being very forthright about their frustration at not being able to determine what the core of Pluto looks like.
They don't know if Pluto has a rocky core or if it is a uniform core.
NASA shows and demonstrates how there are two possible scenarios that could exist and quite frankly no body really know which one it is.
So my theory about the icy core model holds just as much weight as the rocky core model. Only difference is, I'm pretty much alone with my supposition whereas everyone else is comfortable with the other supposition. If common consensus is the measure of successful science then I am wrong, if on the other hand, reason and facts are the rule then my model makes more sense.