What is the part you think is impossible? The part where they live in big atmosphere-filled domes? The part where they grow crops in a similar situation? What part of creating a way for people to live on Mars is outside the capability of our technology and imagination?
Imagination is cheap. I can imagine a unicorn that shits gold, and cures all diseases with a touch of its horn, but that doesn't mean it exists. It's only useful to talk about practicalities, and the fact is that everything you listed is outside of our technology today.
Everything.
Every. Thing.
We have never made a self-contained human supporting ecosystem in a box. Seriously. It has never been made, and not for lack of trying. It is really difficult. Case in point: Biosphere 2[0]
There is no breathable air on Mars. You go outside. You die.
There's no magnetic field, and so the surface radiation is a lot higher there. You stay on the surface for a martian year, your chance of terminal cancer goes up 5%[1] And we haven't even discussed what the people are going to do once they get there. Seriously, there's no resources to make it pay.
As Bruce Sterling put it[2]:
> I'll believe in people settling Mars at about the same time I see people setting the Gobi Desert. The Gobi Desert is about a thousand times as hospitable as Mars and five hundred times cheaper and easier to reach. Nobody ever writes "Gobi Desert Opera" because, well, it's just kind of plonkingly obvious that there's no good reason to go there and live. It's ugly, it's inhospitable and there's no way to make it pay. Mars is just the same, really. We just romanticize it because it's so hard to reach.
