By Colonies 'in' the outer solar system I mean the various moons and space stations past the asteroid belt.
Currently the Hegemony has established bio domes, mining stations, and a few large scale space colonies either on the moons of the outer planets or in close proximity (as well as some Centaurs like 2060 Chiron), but heating these worlds through mechanical means (space heaters) is expensive. If they could find a way to use natural systems already in place it would save them trillions of tax payer dollars.
Now my question is: How would you heat these colonies (the moons themselves) by using or manipulating natural systems? Is there a way, for example, to somehow channel or amplify solar energy, make use of Jupiter's radiation belt, or anything else I haven't thought of?
Note: This is in the context of later terraforming the colonies (in some cases. If its impossible to terraform a certain moon you can just skip over it when answering this question) so the temperature should be at least survivable with limited equipment (arctic temperatures would be the minimum temperature).