Re: Plenty of oxygen on the Moon
Some interesting discussions of the chemistry possibilies of Mars. But I think the big issue has been missed. Why?
"Because it's there" excites explorers. That got us to the Moon, but we didn't stay. And I'd say the same holds for Mars. Musk is fascinated by it and has the money to play with these ideas. But if you want a million colonists, you've got to attract them.
People upped sticks from Europe to the New World from the kind of poverty that even most of Africa is getting out of now. Or from political oppression / religious differences. But there are better places to go to if you've escaped your oppressive regime on Earth. If you want serious numbers of colonists, I don't believe that Mars has much to offer them in the way of hope for the future. People historically have been willing to put up with stuff getting worse, for the promise that their children will be in clover when they're dead - but I don't even see Mars holding out that promise.
Not unless we're talking of terraforming it. Now we don't have to have all the tech, and all the answers now. Just a general idea of what to do. I don't know how much atmosphere Mars can hold, but clearly it would be a lot more if we could greenhouse effect it, and give it some plants. Presumably algaes and mosses to help create topsoil and get nitrogen and carbon cycles going.
If that's not being talked of as a serious option, then I can't see Mars getting more than just thrill seekers.
The other driver of possible colonists is money. Filthy lucre attracts workers, and they need feeding, watering and people to marry (or at least have sex with). But Mars is at the bottom of a gravity well, and is unlikely to produce anything we can't do on Earth - or at least not well enough to negate the hideous shipping costs.
If you're not terraforming, then with the radiaton on Mars what it is, you're eventually going to be living underground. At which point why not the Moon? Which is easier to get off, and closer to Earth? Or even just a space station or an asteroid? We might not live on the Moon, so much as mine it to provide for orbital industries. Or get resources from asteroids, which we can obviously move (if we're feeling brave enough).
What are the sources of money in space? It seems to me there are only a few. Microgravity chemicals, pharmaceuticals and computer chips perhaps? But that's not going to happen unless we already have a presence in space that makes it economic to do the research into what we can actually make. So what can make money now is repairing/servicing/refueuling our existing and profitable satellite fleet - and tourism. All of that is in LEO/GEO, and the tourists might like to visit the Moon.
So it seems to me that mining the Moon for resources to feed industry in Earth orbit is economically feasible, and nothing else is. So nothing else but exploration will happen anywhere else. If we're talking real blue sky thinking, then why not the asteroids? Short of terraforming Mars, you're going to have a better and safer living space there than it's possible to ever get on Mars, and while you're hollowing one out you have space-based resources to sell to other people that need relatively little delta-v to get somewhere useful.
Selling a Mars colony as a backup pool of humans in case of catastrophe to Earth seems too esoteric to get a proper colony going.