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Since Mars has such a thin atmosphere, to terraform we would need massive amounts of Nitrogen. Would it make sense to import it from Venus?
Also since Venus' atmosphere is mostly CO2, and we can make O2 from CO2, could we just import O2 as well? That might be faster than just creating O2 using plants on Mars.
There are easier ways to enhance Mars's atmospheric pressure, so no, don't use Venus materials. I calculated the energy required to lift a kg of nitrogen — or a kg of anything, for that matter — out of Venus's gravity well, and uphill through the sun's gravity well to Mars. Getting it away from Venus was a small part of the total, but that total was nearly 700 MegaJoules, far more than chemically reacting 1 kg of anything could supply. Lugging stuff up the solar gravity well isn't easy!
But there are other ways. For example, there are many objects flying around in the solar system that contain huge amounts of volatiles, such as comets and some asteroids, and some of those are in orbits that are not as difficult to divert to Mars as lugging up from Venus. The savings in energy is greater than the energy needed to make N2 from the NH3 in, say, a comet.
That said, the amount of energy needed for this undertaking currently is far beyond what we can muster.
So no, for multiple reasons Venus shouldn't worry about somebody swiping its nitrogen!
No. Moving N2 or O2 wouldn't make sense, because it would require moving about a quadrillion tons from one planet to another, while we've barely figured out how to move one ton up from one gravity well and down into another.
Once we can do that kind of engineering (pick a favorite technology from science fiction), we may have already become bored with terraforming.
I would like to counter the naysayers. As long as we're dreaming of terraforming, this seems as good an idea as any.
First, I think there's a bit too much hand-waving along the lines of, "Well, once we could do that, we might as well... do... something... else??" That begs the question, "What else?" Two counter-suggestions, namely, using the elements in the Martian crust and using comets and asteroids each bear their own consideration.
Second, I think that there's a lot of heft to the idea of terraforming our solar system as a tandem problem, wherein any solution to the problems of one world may best be addressed by solving an inverse problem on another world. Mars is too cold and its atmosphere too thin. Venus is to warm and its atmosphere too thick.
Still, let's consider the alternatives in depth.
Considering the elemental composition of Mars's crust is important, but NASA-sponsored research has suggested that there likely is not enough CO2 in Mars's ice caps and crust combined to pressurize the atmosphere for a greenhouse effect (source).
Likewise, the same paper cited in the comments doesn't indicate an abundance of nitrogen in the Martian crust that we could use for terraforming. Certainly any serious terraforming effort would require us to maximize the use of resources "on the ground", but if those resources aren't in the ground we have only one alternative: we will have to go somewhere else for some of our elemental needs to make Mars livable.
This is likely to be an important piece of the puzzle, in no small part because it's feasible with today's technology. We know how to land spacecraft on comets and asteroids. Likewise, we could conceivably produce rockets with enough thrust to push comets and asteroids into an impact orbit with Mars.
Further, comets and asteroids have lots of desirable materials relevant to terraforming. Comets in particular are rich in water, CO2, methane, and amonia, which finally gets us the nitrogen from the original question.
My chief question is what would be the actual effort required to wrangle enough comets and asteroids to get Mars's atmosphere up to an Earth-like atmospheric pressure? There probably is enough raw material in the various asteroids and comets around the solar system to bring the Martian atmosphere up to one atmosphere. Indeed, the NASA paper cited above notes this.
Another idea is to import volatiles by redirecting comets and asteroids to hit Mars. However, the team’s calculations reveal that many thousands would be required; again, not very practical.
So, the question is: Is it logistically more prohibitive to put enough comet-chasing rockets into space and then turn them all to the purpose of redirecting the orbits of various small bodies than it would be to cart Venusian atmosphere to Mars? I'm not sure, but let us at least consider the alternative.
One of the chief objections here is the cost of moving the atmosphere out of Venus's gravity well. Yet this is a central problem to most multi-planetary-scale engineering problems with lots of different proposed solutions. I would like to draw attention to the humble skyhook. Sure, it's not as flashy as a space fountain or space elevator, but it could be perfect for mining the Venusian atompshere at scale.
On its descent into the atmosphere, one end of the skyhook could begin pumping material out. On ascent, it could release it into a higher orbit where it could be gathered up and pressurized by an orbital tanker. From there, it could be shipped off to Mars.
Granted, pressurizing a quadrillion tons of atmosphere and shipping it across the solar system is no mean feat. And yes, a skyhook for Venus would be the single greatest engineering feat our species has yet accomplished. Of course, so would putting thousands of comet-moving rockets into deep space. The question is, what are the relative pros and cons of each approach?
The big advantage to Venus is that we begin the process of thinning Venus's atmosphere, which is an important terraforming project in its own right. Another advantage I see over comet mining is that it's just one big problem to worry about, rather than thousands of small ones.
I wouldn't use the gases from Venus for Mars but I would use them for rotating space stations between Earth and Venus. The distances wouldn't be that far and we don't need to worry about how we get massive amounts down to Mars.
A lot of you might dream of giant O'Neil cylinders, but the elephant in the room is the question: "From where comes the air for a structure that houses thousands of people?" Habitats between Earth and Venus can use a constant energy supply of solar panels and would be easy to reach from Earth and Moon However the atmosphere of Venus could rather support a swarm of space habitats than a terraforming project on Mars.
When it comes to getting an atmosphere on mars I would, as already said in the discussion, use comets, because they are mostly made out of water, ammonia, CO2-ice, silica and other abundant alkaline metals. We could just throw them down on Mars. The ices would melt and release the gases and supply Mars with more water. We should know that here on earth most of our breathable air comes from algae, tang, plankton and bacteria in the oceans.
A stationary magnet on the L1-point, and the use of processed fluor-hydrocarbon gases out of Mars' crust also help to get a warm atmosphere.
Terraforming Mars would be a futile task as the atmosphere you would give it would corrode away without an electromagnetic sphere protecting the planet from solar winds. And say you could undertake such a massive mission taking it from Venus would be extremely uneconomical as previously stated. Also remember how volatile the winds on Venus can be. Let's say that you can terraform Mars and want to do so although you know that whatever atmosphere you do make will simply disappear soon enough, the planet is dead, and humans of the distant future would condemn us for wasting resources on such a great magnitude.
Yeah you could do that. It would take a fleet of autonomous nuclear thermal spaceplanes. Basically the spaceplanes dip into the atmosphere using externally heated turbines with ambient air as propellent while it sucks up and compresses ambient atmosphere. Use a portion of the atmosphere you just collected to leave the gravity well and trasport to a gigantic reservoir nearby. The reservoir goes near mars and then drops small iron cannisters to imlact the surface filled with pressuried venus atmosphere. The reservoir refills on iron cannisters from a mass driver up mount olympons. You would need hundreds of these reservoirs, 1000s of autonomous space planes, and decades of constant work. To be clear, these reservoirs make aircraft carriers look like a canoe.
To all who say the solar wind and mars magnetic field blah blah blah just be quiet. Its a non issue. A satellite inbetween mars and the sun of just a few tesla is more then adequate to shield mars. Sure the satellite will need maintenance but atmosphere bleed off happens over millions of years, and its not technologically difficult to make a satellite, just economically difficult. The real question is why the hell would anyone want to terraform anything to begin with? Rotating space habitats can be made into a paradise. Screw getting close to good, choose great instead. Space habitats are objectively better in every way compared to a planet.
