so in all likelyhood there is at least one planet past the kuiper belt responsible for whats called "the kuiper cliff", it would be orbiting 50-100 au, be between a mars mass and 2.5 earth masses, and given the temperature would likely have a thick helium atmosphere and a crust of volatiles (methane, ammonia, ntriogen, water) over a rocky core. Could this planet be a good prospect for colonisation given its energy abundance (helium 3) and thick atmosphere , sure it will be cold but aerogel should suffice, it would have little radiation and likely would have MANY MANY moons from captured kuiper belt bodies.