[bryanlarsen]

They're not viable candidates as backup plans for humanity because they have the same vulnerabilities to comet strikes, global nuclear war and pandemic as the rest of the Earth.

OTOH, if one of those took out human life on Earth, people living on Mars could re-colonize Earth.

[amanaplanacanal]

Earth after a global nuclear war or comet strike is still more hospitable than Mars.

It's hard to imagine anything that would make Mars a better place to live than simply staying on earth.

[bryanlarsen]

Yes it would be. But that doesn't matter if no humans make it through the apocalypse in the first place.

[amanaplanacanal]

The moon would do the job at a lot cheaper price.

[bryanlarsen]

Nope. Because of aero braking, Mars takes less delta v to get to and land on than the moon does.

[amanaplanacanal]

Now I'm wondering why the Apollo program went to the moon if doing Mars is so much cheaper.

[bryanlarsen]

Going is cheaper. Coming back is more expensive. And of course the 3-6 month travel time is a challenge.