Thermal forces? Someone is going to have to explain what that is.
Well, I guess it's possible that, if frozen gases on were exposed to direct sunlight, the thermal energy might be enough to cause the frozen gases to thaw enough for it to act as a "rocket exhaust" and launch it out of the belt, where gravitational forces would take over ...
I'm not a scientist (mad or otherwise), although I have played one on the stage ...
Heat from the sun causes ice to sublimate on objects in the Kuiper belt and the small jets of the escaping vapors send the object on a death plunge into the sun’s gravity well..............