What we know about our current solar system is irrelevant. We are possibly thousands of years in our future. The Traveler has changed many things about the planets we have seen. It is even possible that he has changed the orbit of planets in order to terraform. There are also some therories based on Grimore cards that we are actually in a Vex matrix. We might not be on any of these planets, but are just living in a Vex program. Our reality is whatever the Vex makes it then. We dont know enough to say something isnt possible.