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[mainiac]

You dont need to terraform mars, you need to build greenhouses.  And mars has atmospheric nitrogen which could be harvested for the small amount of nitrogen needed.  We dont add nitrogen fertilizers because we need vast quantities of nitrogen, we add them because most of the nitrogen in the world is in the wrong chemical formula.  So you just collect atmospheric nitrogen on mars, use solar energy to process it and make your fertilizers.

[MonkeyHead]

You dont need to terraform mars, you need to build greenhouses.  And mars has atmospheric nitrogen which could be harvested for the small amount of nitrogen needed.  We dont add nitrogen fertilizers because we need vast quantities of nitrogen, we add them because most of the nitrogen in the world is in the wrong chemical formula.  So you just collect atmospheric nitrogen on mars, use solar energy to process it and make your fertilizers.

I assume legumes could have a useful role here?

[mainiac]

They would also do the trick if you put them in a greenhouse with a terrestrial atmosphere.

[monkey]

Mars has barely an atmosphere and 1.8% of that nothing is nitrogen.
Even Kim Stanley Robinson in his otherwise utopic scifi book Red Mars had put vast amounts of nitrogen underground because it was recognized as a problem.

[mainiac]

Surface pressure on mars is 0.087 psi.  That's 61 million kilograms per square kilometer.  Surface area of mars is 56 million square kilometers.  That's 3.4*10^15 kilograms of martian atmosphere.  Of that 2% is nitrogen.  That's 69 billion metric tons of atmospheric nitrogen on mars.  The earth used about 190 million metric tons of agricultural nutrients of all forms last year (page 12).  Unless you are envisioning a population of many hundreds of billions that's a lot of nitrogen.  If you want to teraform the planet you'd need a lot more and you'd have to hope there are rocky deposits of the stuff.  But for greenhouses that's plenty to sustain centuries of exports.

[origamiscienceguy]

I don't know about anybody else, but I think that the earth is by far the most beautiful planet. So I don't want to be separated from it for a long time. Anybody else feel that way?

[Fniff]

I like Earth, but... it's like living in a house for fifty years. Even if it's an amazingly beautiful villa, you're going to want to see something else after a while.

[GiglameshDespair]

Surface pressure on mars is 0.087 psi.  That's 61 million kilograms per square kilometer.  Surface area of mars is 56 million square kilometers.  That's 3.4*10^15 kilograms of martian atmosphere.  Of that 2% is nitrogen.  That's 69 billion metric tons of atmospheric nitrogen on mars.  The earth used about 190 million metric tons of agricultural nutrients of all forms last year (page 12).  Unless you are envisioning a population of many hundreds of billions that's a lot of nitrogen.  If you want to teraform the planet you'd need a lot more and you'd have to hope there are rocky deposits of the stuff.  But for greenhouses that's plenty to sustain centuries of exports.

Sure, it's there. But that's a lot of very thin atmosphere you have to process to get that nitrogen. To get that nitrogen out of the air, you'd probably use the Haber Process. This requires a lot of pressure, heat, and power. The atmosphere's not fun to work with, either - at 95% Co² it's both too thin to breath and if you tried it'd poison you anyway. It's also poisonous to plants, but that's beside the point. It's over four times the partial pressure of CO² to kill plants, in fact. Not good for the lungs.

There's a hell of a lot of difference in pressure between the martian atmosphere and the pressure you need for the Haber process. The Haber process is generally done at around 200 atmospheres. That's with the 78% percent nitrogen content of Earthly atmosphere. You're going to need a lot more heat and pressure to make it possible on Mars and that makes the whole process much more difficult.

You'll need a lot of energy (Haber process consumes between 1 and 2% of the world's energy use It ain't cheap.). How would you supply this? Solar, maybe, but that's a lot of solar panels you need to take, and then maintain against the sand-blasting of Mar's surface.  Nuclear fission isn't practical on Earth, yet, never mind sent across space to Mars.
Fission is a maybe, but if things go wrong you've then got radioactive material strew across the place. There's a few other problems - how will you keep it cool? Water? It'll need a lot of water. Martian air is pretty cold, but thin air is quite a good insulator.

These things aren't as simple as it appears.

[mainiac]

Condensing gas and separating N2 from CO2 are trivially simple engineering problems.

[GiglameshDespair]

You still need to do things with that nitrogen, which means Haber process.

Concentrating the air? Yeah, simple. Pump it into a cylinder. But that takes energy. That takes materials.

Most common method of air separation seems to cryogenic separation. High purity gases, but energy intensive.

[WillowLuman]

Not as tough when the temperature outside is regularly below 0C. Unless it relies on temperature differentials, of course.

[mainiac]

You are talking about a task with less mechanic stress and power needs then inflating an air mattress on earth.  A very small mechanic device and very small electrical generation capacity will suffice.

[alway]

I don't know about anybody else, but I think that the earth is by far the most beautiful planet. So I don't want to be separated from it for a long time. Anybody else feel that way?

Pretty much. Especially since if we lived in space, we would effectively be confined to the equivalent of a small apartment building, with the exception of the occasional bothersome trip outside to wander around the wasteland (or nothingness) for a while. And with internet latency of 90 minutes to earth, you're isolated to the point where you're practically sending letters to communicate.

Ideally, you would eventually modify the humans on Mars to be able to live there as naturally as on Earth, but such bio-engineering will likely only be in its infancy by the end of our lives; and so they would be stuck in their tiny apartment building for the rest of their lives.

[WillowLuman]

Theoretically they could just build a really big apartment building.

[Arcvasti]

Or, Y'know, just siphon off some atmosphere from Venus. Its got too much of the stuff[Although it might not be the right composition? Space is hard.].

^Please interpret above inane suggestion as a creatively worded PTW