There's one thing that would probably prevent humans from living on Mars that we can really never change: the gravity is wrong. There is no evidence that human

There's one thing that would probably prevent humans from living on Mars that we can really never change: the gravity is wrong. There is no evidence that human gestation and growth is possible in a net g field less than 9.7 or larger than 9.9. For all we know, no outside-Earth colony is possible without artificial gravity or extensive genetic engineering. No foreseeable human contrivance stands a chance of changing the mass of Mars — and even if we could, it's orbit would be knocked wildly off course and possibly destroy the balance in the inner solar system. Even Venus is ruled out by gravity. So these terraforming plans might allow us to visit Mars, but not to live there, at least not in the foreseeable future.