Let's say there is a planet that is in the middle of nowhere so it isn't moving all the time like a planet in a solar system. The pressure caused by gravity pulling down towards the centre of mass (the middle of the planet) would heat up the core of the planet.
Couldn't this be used as an infinite source of thermal energy? If not could someone tell me why?
I know that gravity is a force and energy cannot be created nor destroyed. Objects can gain potential gravitational energy by being pulled further away from let's say a planet but this requires energy to do. So does the energy come from the time when the planet formed and the matter became a ball?