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Most of all the articles about Mars terraforming focus on warming the atmosphere. 2nd most popular topic as far as I know is the magnetic field that Mars lacks. Some other sources speak about toxic soil too. All of that sums up the terraforming as impossible today.

But what would happen if we already warmed up Mars (eg. with CO2)? Its atmosphere would consist of around 99% CO2 then and would lack oxygen and nitrogen. We could start production of oxygen using eg. ecopoiesis, but as it would lower the amount of CO2 wouldn't it also cool the atmosphere down again?

So let's put money and time aside: What would hypothetical chronological roadmap of what should be done in order to terraform Mars look like?

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It's a bit of a late answer, but most proposals don't actually use increased CO2 to warm up the planet. They use super-greenhouse gases (like perfluorocarbons), or they increase the amount of sunlight hitting Mars.

As for a terraforming roadmap, there's one by Robert Zubrin, which proposes that it would take about a thousand years. However, others argue that it would take thousands of years. Making an atmosphere breathable to humans appears to be the most time-consuming step. The earlier steps (warming up Mars, thickening the atmosphere etc.) would be comparatively short, taking a century or maybe even just a few decades.

Personally, I doubt that such expensive and time-consuming projects would ever be performed. I think a more realistic approach would be a compromise: rather than making at atmosphere breathable to humans, it would be more practical to aim for an atmosphere that can support plants. Plants can tolerate less oxygen, lower atmospheric pressure and higher CO2 than humans can. Some animals might be able to survive in this atmosphere as well. Humans would need to live in sealed habitats, but those habitats would be much easier to construct than on the present Mars, and humans could go outside with just an oxygen mask. This kind of terraforming could potentially be completed within a human lifetime. But it's questionable if this could even be called "terraforming" anymore*, and of course it would still be more expensive than any project that humanity has done to date.

One hypothetical roadmap might be this:

  1. Study every aspect of Mars extensively. This is necessary for terraforming to have any chance of success, and also to leave a record of the original Mars.
  2. Test the terraforming techniques extensively, in Earth labs simulating Martian conditions, and also in labs on Mars itself (carefully sealed off from the outside environment).
  3. Add perfluorocarbons to Mars' atmosphere, warming it up and also thickening the atmosphere slightly (by sublimating the frozen CO2 and releasing adsorbed CO2 from regolith).
  4. Seed Mars with various genetically modified bacteria, which break down the toxic perchlorates in the soil, bind together the soil (to reduce the dust storms), digest nitrate minerals (adding nitrogen and oxygen to the atmosphere) and produce oxygen via photosynthesis. At the same time, robots could be used to begin building habitats for humans.
  5. Add plants and animals, and begin human colonization.
  6. Build an artificial magnetosphere for Mars, to help it retain its atmosphere (https://www.extremetech.com/extreme/245369-nasa-proposes-building-artificial-magnetic-field-restore-mars-atmosphere).

*: "semiterraforming" might be a better word for it

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  • $\begingroup$ Adding perfluorocarbons faster than Mars will loose it might be a problem. $\endgroup$ – Uwe Jul 24 at 7:26
  • $\begingroup$ @Uwe If you're talking about how Mars loses its atmosphere to the solar wind, this happens over very long timescales: forbes.com/sites/startswithabang/2017/03/03/…. $\endgroup$ – Pitto Jul 24 at 10:18
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The most important problem is that today we can't even terraform the Sahara desert.1 Thus, having an objective project plan is the far future yet.

Not only $\rm CO_2$ has greenhouse effect. According this answer, the average temperature of an Earth without any athmosphere would be around $\approx \rm 0^\circ \rm C$. The current average temperature is $\approx \rm 15^\circ \rm C$. Most of the difference isn't caused by $\rm CO_2$, but by water vapor and air.

The soil toxicity - large mass of perchlorate salts - seems probably solvable, probably with at least a little genetic engineering. There are highly sodium perchlorate tolerant bacteria. But there is no known organism which could survive and grow in the lack of water.

Although a lot of water was found on the Mars, this "a lot" is only compared to what we knew before the probes. The total known water mass of the Mars makes the whole planet still so dry, like a desert.

1Although it would be technically possible, currently both money and politics avoids us to terraform the Sahara. An USA + China cooperation and some hundreds billions of $ could do it. I think the Martian SpaceX colony will happen first.

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  • $\begingroup$ "today we can't even terraform the Sahara desert" is wrong. It's about money and politics. Also, there are in fact many "objective" plans for terraforming Mars, i.e. which should work in theory. $\endgroup$ – Everyday Astronaut Jul 24 at 11:42
  • $\begingroup$ @EverydayAstronaut Yes. Both money and politics avoids us to terraform the Sahara. An USA + China cooperation and some hundreds billions of $ could do it. I think the Martian SpaceX colony will happen first. $\endgroup$ – peterh - Reinstate Monica Jul 24 at 11:47
  • $\begingroup$ @EverydayAstronaut I think I did it. $\endgroup$ – peterh - Reinstate Monica Aug 2 at 12:08

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