Terraforming an Earth-like Planet

Question

I have been recently thinking and writing about a hard sci-fi universe with the exception of FTL. Within the system of Alchiba (or Alpha Corvi) lies a planet under the name of Mannhardt and is an Earth-like with no life and an unbreathable atmosphere which contains too much CO2 and other toxic gases from volcanic activity. Here is some general information on the planet that I copied from a concept art for the planet I made:

TYPE: Rocky world with water

DIAMETER: 10,889.52 km

GRAVITY: 8.81 m/s² (0.898 G)

TEMPERATURE: -27 °C to +33 °C (8 °C average)

ATMOSPHERE: 63.3 kPa (0.625 ATM) | Carbon Dioxide (68%), Methane (7%), Water Vapor (5%), Oxygen (5%), Ammonia (1%), Other gases [ex. Propane, Hydrogen Sulfide, etc.] (1%)

“Alchiba b is harsh but strangely beautiful planet which had begun colonization only a few years ago. Its atmosphere is unbreathable and poisonous, but it still has oceans, lakes, and rivers of liquid water. It lies within the habitable zone and is undergoing terraforming. The skies are surprisingly blue and the ground mostly consists of sand and volcanic rocks. The planet has large oceans and landmasses and islands which are carved by erosion with steep and sharp cliffs and sprawling valleys, canyons, and mountain ranges. There is a fair amount of volcanic activity releasing gases into the atmosphere. The planet is swirling with clouds and weather systems which deposit water across its rough and craggy plains."

CONCEPT ART ITSELF: https://zertofi.deviantart.com/art/Planetary-Concept-MANNHARDT-728602681

Now I was wondering how long would it take to terraform this planet. More specifically make the air breathable. I was thinking somewhere of upwards to a couple thousand years but I am not sure. Within this universe I have giant terraformers which expel and take gas from and into the atmosphere which can be up to the size of a small city. If hundreds (or thousands) of those are placed across the planet including other methods, how long would it take to make this planets atmosphere breathable?
You don't have to provide any mathematical equations (unless if you want) but just an estimate or guess.
Thank You.

Answer 1

You would never terraform with giant machines. It would be slow, expensive and unreliable.

Life is the ultimate terraformer. Humans would sit up in a space station control centre and spray genetically engineered bacteria and algae around the globe.

You engineer the lifeforms to eat up the chemicals you don't like and release chemicals you need.

Life already on earth survive in many extremes places so it would be quite possible to build lifeforms to survive and prosper.

Once you get the planet to the level to support more complex life, you start sowing plants (trees, grasses, seaweed). Once plants are established, you release insect life and other simple life forms and keep going on from there.

All people would need is a giant computer system with a database of DNA and the gear to genetically engineer life. The operators could use remote monitoring and cryosleep to skip the waiting between each step.

You should be able to make it suitable to human life within hundreds of years since you don't have to alter temperature, gravity or solar radiation.

Answer 2

Let's paint it in really broad strokes, shall we. Also, let's assume that biological method suggested by Thorne is not feasible for some reason, for example due to lack of nitrogen. We will also assume you want to process all CO₂ that's there. Given that 450 ppm (parts per million) is dangerous, we can assume you just want 0 of it.

Total mass of Earth atmosphere is 5.1480×10¹⁸ kg. Really wild approximation is that you have 0.625 times that much, and 0.68 of it is carbon dioxide. This gives approximately 2.2×10¹⁸ kg of carbon dioxide, and 3.22×10¹⁸ kg of air to process.

Speed of sound on Earth is about 343 m/s. You don't want to go even near that. So we will assume you can suck air at 100 m/s, to keep it safe. You said that your atmospheric processors are as big as small city. That makes them about 10 km wide. I'd also say that 1 km tall is what we can use. This makes it 10 square kilometers of input area, if it's on one side. Very nice number for calculations. This gives processing speed of 10⁹ m³ / s. On Earth, 1 kg of carbon dioxide is about 2 m³. But under your lower pressure and considering dilution in other gases it'll ble closer to 3 m³.

This give very, very rough estimate of 3×10⁸ kg/s, and you have 3.22×10¹⁸ kg gas to process. Surprisingly, this gives only 340 years.

In reality, this would be much longer for a lot of reasons. Air already processed will mix with air that needs to be processed, making process slower as you go, making it really hard to finish the process. Pressure will drop as you remove carbon from gas. And so on, and so on. My intuition tells me that it'll be like 3 times more to get to a point when big machines no longer make sense. On the other hand, you can drop many machines on the surface.

This by no means is exact calculation. But if you need a timescale that does not seem too wild, then a thousand years divided by number of mega machines looks like something that could potentially be done, with such massive effort.

Worth noting, removing 1 kg of carbon from carbon dioxide would cost you around 3×10⁷ Joules. That's a total of 1.8×10²⁵ Joules, even assuming reasonably perfect process. You will need to pump a lot of energy into your baby planet.

Answer 3

Thorne's solution is the accepted easier way, geoengineering requires too many resources and is not scalable, while life scales up from a small sample. These sort of discussions have been taking place in the scientific literature for quite a while, see:

Graham 2004, The biological terraforming of mars: planetary ecosynthesis as ecological succesion on a global scale. ASTROBIOLOGY

Bains & Schulze-Makuch 2016, The cosmic Zoo: the near inetability of the evolution of complex, macroscopic life. LIFE

Sole et al. 2015, Synthetic circuit designs for earth terraformation. BIOLOGY DIRECT

A common point of contention in the discussions about bioengineering biospheres is that evolutionary forces will obviously still be acting, which can yield unexpected results, divergent from what was planned. There are some methods to control these effects, discussed more in depth in the 3rd paper.

Answer 4

First I would like to point out some flaws within your planets design and point out things that would occur on this planet that you might not have realized. I would also like to show some pre-existing conditions that would affect colonization significantly.

The Air

I would first like to point out your atmospheric composition is unrealistic, not only is there the fact that you only list the composition of 89% of your atmosphere and leave the other 11% unlisted but you also have some slightly unrealistic numbers. First of you list 5% of the atmosphere as containing oxygen while 7% of the atmosphere contains methane, these two things react very well together and you are likely to not have any O2 left after only a few years. So I will change the atmospheric composition a little bit to fit real world chemistry by simply causing the O2 to react with the methane and then change the values accordingly. So when 2 O2 molecules react with 1 Methane it produces 1 CO2 molecule and 2 water molecules, so if we do some simple arithmetic we find that after reacting all the methane in your atmosphere with all of it's O2 then 4.5% of your methane will remain will 2.5% will react, about 7.5% of your atmosphere will participate in this reaction and now we can safely say that an additional 2.5% of your atmosphere will be CO2 (1/3 of the reactents) and an additional 5% will be water vapor (2/3 of the reactants).

The final atmosphere is 70.5% CO2, 10% water vapor, 4.5% methane, 1% ammonia and 1% trace gases, and finally 11% nothing. That is still a problem, 11% of your atmosphere is unaccounted for within your post, because of this I have to make some sort of decision as to what that 11% is (and it's obviously not oxygen), I would say actually figure out what that final 11% of your atmosphere is made of but for the sake of this post i'll just say it's nitrogen. Why nitrogen? well you already have Ammonia which is nitrogen based, this shows that you have some amount of nitrogen on the planet and I wouldn't think that all of it is found in the relatively unstable molecule of ammonia (at-least compared to the super-stable N2) so I'll say it's N2. The second reason is because it will help with terraforming.

The oceans

I would like to note that you're oceans (and other bodies of water) would have a-lot of CO2 trapped inside, the oceans would actually be heavily carbonated and more so then soda and some of the biggest eruptions will simply be water bodies ejecting CO2, you could have exploding lakes that are cause solely because the water is trapping CO2 that it gets from the atmosphere, it will also contain ammonia and methane and other things which will seriously affect the drinkability of the water but, as far as I know, a significant hydrosphere is still possible, even probable. however your land should cover less then 50% of the land, between 20 and 40% would be safe, it will make a significant hydrosphere more probable and make your maps look better due to negative space.

Pre-existing life

Now when I looked at your concept art I saw a-lot of brown, a good amount of blue, but I also saw some green. I don't know if you intended to mean this but it looks like, from your concept art, that there is a tiny bit of pre-existing life on your planet. So I want to consider what this life might look like if you decide that it does exist.

First of the composition of your atmosphere (and also the modified one I made for the sake of the post) actually makes photosynthesis better. First off the products of photosynthesis are oxygen and organic molecules, the oxygen produced can react with the methane with very very little catalyst and the reaction between naturally inhaled methane produces all the necessary inputs for photosynthesis except for light, which is easily accessible, and the process can be repeated over and over again with each photo-synthetic reaction producing the oxygen needed to perform the methane reactions which produces what is needed for photosynthesis; this, along with the continual input of methane from volcanoes, allows for plant life that can sustain itself continually as-long as volcanoes remain active. you can have plains, legitimate plains, and even forests all throughout your world and not just single-cell bacteria before your colonists even get there.

now for the colonists

Now the thing is this planet is just to good, it's to good as in it is so close to earth that there is no reason NOT to set up colonies right away, after all the gravity is relatively close to earths (probably a bit to low for a safe pregnancy but probably enough to keep the average person healthy enough to go in a 1g environment), almost all the necessary elements for life are available (though not in exactly proper quantities) the temperature is amazing and there is life there already, since earth bacteria probably can't survive in such a methane heavy atmosphere you probably also don't need to worry about that at all and you can think about other things.

So initial colonies will likely be large structures that look similar to those on earth with small pregnancy wards that are at 1g and exercise wards at even higher gravity cause, why not. The colonies will be able to manufacture 100% of their air on-site by getting the oxygen from the CO2, the nitrogen from the... Nitrogen and they can get essential water from a nearby lake or river after they process out the harmful chemicals.

They would likely begin with taking their own crops to the world but would likely experiment with local vegetation to see if any of it is edible and some of it might, a grain crop or some other mass pollinator that relies on the wind, but nonetheless it is a very suitable world for humans to live on.

but as for terraforming it can be done, the only thing the planet would really lack is a proper amount of nitrogen which it will have to import from another planet, since you list that there is FTL the imported nitrogen does not have to be from the Alchiba system so you don't have to build a N2 heavy planet, other then that all that needs to be done is the removal of almost all of the CO2 (you must have some for earth-plants to survive) and all of the methane and ammonia, it seems to me like you might need to remove some of the atmosphere during the terraforming process to make room for the nitrogen and prevent the surface pressure from becoming to high and once this is done you can make a planet almost like earth, sure you need to add a biosphere and make a breathable atmosphere ad make the oceans stop exploding but that is possible.

As for the timeline If you have many factions they will be fighting wars for this planet, it is just to good, it is so much like earth (probably more like earth then any other planet except earth) and the ease of terraforming it is so great that it will be seen as the single most important planet in the galaxy, except for earth. because multiple factions are fighting over it the terraforming process will be slow and there will be many setbacks and alternative approaches that the empires will place upon it, that is until the planet itself becomes powerful enough to found an empire of it's own which is when the terraforming will really get going.

I would suggest that a real, focused, consistent terraforming effort to form on the planet would take about 400 years due to historical forces, after the 400 years it might have the power to protect itself as it continues to make the planet more earth-like for the next 500 years, so about 500 years of concentrated and consistent effort would make the planet almost habitable with it being likely that the methane would be processed out by then especially with the oxygenation of the atmosphere, the de-methanization of the atmosphere along with the oxygenation of the atmosphere would kill any pre-existing life relying on methane as it's main source of energy though classical plant life can exist and survive, this would make an interesting Earth-Mannhardt co-born biosphere could form with the animals almost exclusively coming from earth while the plant life is a mix of Earth and Mannhardt plant life.

But what your interested in is the time it will take, I would say about 1100 years as a middle-estimate, this conisiders that there is atleast a 400 year period of political instability and one major setback afterwards, if one power is able to control the entire planet from the beginning the number can be shortened to 900 years but in the most likely scenario where there are multiple setbacks of political origin (such as re-conquest after 500 years of independence or the political fracturing of the planet itself) you could be looking at 1500 years.

And here are the stages

You can have massive atmosphere processing machines alright, this is actually a very good ides as what these machines can do is they can break down the CO2 into O2 and use the remaining carbon for graphene production and then they can release the O2 back into the atmosphere which will react with the methane and make more CO2 and Water Vapor, all in all though the first part of the terraforming process would produce almost no oxygen it would add more water to the world and remove deadly methane. Indeed the removal of methane is simply done to allow for the creation of a earth-like atmosphere as a high amount of methane can't exist along with a high amount of O2.

Once the methane is removed these stations will begin to actually increase the oxygen in the atmosphere (note that there is already some O2 due to the early colonies but this has a negligible affect on the atmosphere) and the CO2 will slowly fall, you will want to ship some of the CO2 off-world to make room for a proper amount of nitrogen but not close to all of it. Now the ammonia probably isn't a big deal as colonies would likely begin to harvest the ammonia for it's various uses from the beggining lowering the ammonia content of the atmosphere over time. Once you put all this together the atmosphere is terraformed.

With a large amount of carbonated water you will also have to change the chemical makeup of the oceans by purifying the water over a long period of time likely by sending in genetically engineered bacteria that are engineered to die out as soon as their mission is complete (removing a certain poisonous gas from the sea) by making the thing thy are removing essential to their existence, however you would also likely treat the water directly with machinery to speed up the process. In the end you would have to remove the explosiveness of the seas and make it possible for fish to live there but this will probably take more then 2000 years (the planet would still be sufficiently terraformed for humans to be able to live outside with no protection long before the seas can have fish) but the change in the atmosphere will actually affect the oceans as-well.

Finally all this method that i am proposing would likely destroy any biosphere your planet might have but some plants and bacteria might be able to survive, and any plants or bacteria intentionally kept alive by humans because of their utility will. Nonetheless the planet can easily support an earth-like biosphere with only a little tweaking and you should be fine.