Serious question: How do you get the energy (and other resources) back to earth in a way that is cost competitive with extracting them here? If it costs more money, people will use up what's here before they import the resources from Mars.

Bringing a thing from space down to earth should, if we're smart about it, be a free source of energy. If it's very expensive instead, that's from some combination of insufficient capital base and poverty of ideas. For instance, a skyhook -- a spinning tether in orbit -- could lower one payload into the atmosphere and boost another into space, at no net energy cost.

A pretty good, if very old, popular intro to this kind of thinking was Heppenheimer's Colonies in Space (free on the web now).

Mars seems unpromising because it's at the bottom of a gravity well, has an inconvenient atmosphere, should be preserved for scientific research while there's still a chance of traces of life, etc. Asteroids seem way more useful, and the Moon is nearer.

So, polluting 2 worlds instead of one? Nobody will stop exploiting Earth even once new worlds become accessible.

I'd much rather pollute Mars, a dead rock, than the Earth.

Agree, yet it's not an either Mars or Earth question. Judging by priorities of corporations (making money, of course) it will certainly be both Mars and Earth.

In fact, the whole concept of "pollution" on Mars makes little sense. We could convert it to radioactive slag and plaster it with "Eat at Joe's" billboards, and it wouldn't hurt anyone or anything.

What we ought to be doing with Mars is terraforming it. I'd start by collecting extremophile bacteria from Earth and letting it loose on Mars and see if any of it takes hold.

> polluting 2 worlds

How are you polluting another world if there is no life there in the first place?

Good question. Perhaps. However, my point still remains that it will not stop the pollution on Earth - which will remain much cheaper to do.