It's not really possible short of extreme megatechnology. Anyway you've got to ask if it would last long term.
First there's the idea of warming up Mars. The cheapest is probably to use greenhouse gases. But though that's much easier than mirrors with an area similar to that of Mars itself, it's still pretty tough. It is only easy by comparison with other solutions.
The problem is that at present the Mars atmosphere is in an equilibrium where if more CO2 is released temporarily, it will just turn back into dry ice again at the poles. So you need a permanent on-going way to keep it in the atmosphere. That is - unless you can push the amount of CO2 up over the magic number of 10% of Earth's atmospheric pressure. If you do that you get a runaway effect.
But that involves releasing, somehow, 100,000 cubic kilometers of dry ice into the atmosphere. If that exists at all. So far we know of a deposit with 10,000 cubic kilometers. If we somehow could release all of that into the atmosphere, it wouldn't 'be enough to start a runaway greenhouse - it is an order of magnitude too little - it would just all condense back to the poles again.
We don't even know for sure if Mars has enough CO2 to reach that magic 10%. If it did, then it would then all evaporate in a runaway effect until all the CO2, however much it is, goes into the atmosphere.
But the "easier" approach is to use greenhouse gases. Instead of turning 100,000 cubic kilometers of dry ice into gas, you "only" need to mine 11 cubic kilometers of fluorite. A dramatic improvement. And what's more, it makes the tipping point lower, so you don't need to go all the way up to 10% of Earth's to start the process going.
Nevertheless - that means 257,000 times Earth's current yearly production of those gases for a century. And to power that, you need 245 half a gigawatt power stations on Mars all operating 24/7 for a century, just making greenhouse gases. And all the mining technology to supply those factories with ores, searching the planet for fluorite ores and anything rich in fluorine to return to your factories.
That is what they call the "easy way" to create a dense atmosphere on Mars.
More about that here: Why Nukes Can't Terraform Mars - Pack Less Punch Than A Comet Collision
And then remember, that CO2 is actually poisonous to humans above 1%, so even if you can get oxygen as well somehow, all that CO2 you used to warm the planet has then to be converted back into plant matter, peat, trees etc. And when you do that, of course the planet,without all that CO2, cools down again so you have to step up your production of greenhouse gases to compensate and continue that long term. Or by then you might decide it is easier to build your huge mirrors in space, with area similar to the surface area of a planet, to double the amount of sunlight reaching the Mars surface.
And you have to supply all of the nitrogen as a buffer gas. Plants aren't going to supply it as they produce oxygen, not nitrogen. You have to mine it and extract it if you can find it. Or if there isn't enough as there very well might not be, then import it from comets or the like.
And the timescale, for producing the oxygen once you have your dense CO2 atmosphere (if you get that far, and to get that far probably would take 1,000 years, if it is possible), if you look at the studies, Chris McKay estimates 100,000 years to generate enough oxygen to breath in the atmosphere- at the end of which the surface is covered in organics to a depth of many meters, taken out of the atmosphere by plants. And that is of course a huge speed up over the hundreds of millions of years it took for Earth.
But then the main thing is that Mars is not like Earth. Lower gravity, which means you need three times as much of everything by mass for the same atmospheric pressure. Your plants have to work three times harder. But it is also further from the sun. So they get only half the light they do on Earth. And it's colder, even after all that warming, it will be some time before you get to temperatures where trees can grow, even when the atmosphere is thick enough. Indeed, they reckon you'd need to continue to produce large quantities of greenhouse gases in perpetuity to keep the planet warm enough for trees.
And then on the very long time scale of millions of years - well Mars will surely lose all its water again, what little it has left that you managed to liberate with your terraforming. And the carbon dioxide probably turns into carbonates, because it has no continental drift.
So - in short, it's a fascinating idea intellectually. But - short of some really game changing ideas and technology, it is a hugely difficult task. Far harder than the science fiction writers make it out to be.
Remember they are good at writing entertaining and thought provoking stories. But their speciality is not an ability to predict the future. Sometimes they get things right but sometimes they fail hugely. E.g. all the stories about thick drifts of dust on the Moon, then when we got there, the dust is only thick enough for a footprint. No chance at all of astronauts sinking into it out of sight. Right up until a few years before the Apollo landing, sci fi writers were writing stories about these dust drifts on the Moon. Arthur C. Clarke's famous, very hard sci. fi. A Fall of Moondust was published eight years before Apollo 11 - he has an entire lunar cruiser disappear into a lunar dust drift right out of sight without a visible trace on the surface.
Or stories about far future astronauts using slide rules to help pilot faster than light spaceships - for instance Robert Heinliem's "Slip-stick Libby" is a dab hand at slide rules, how he got his name, and in Methuselah's Children he uses one to make last minute adjustments to his novel faster than light space drive.
It was published in 1958 but in the 1960s when I was a young teenager, such stories didn't seem anachronistic, but rather - the slide rule was a mark of hard sci. fi.
Now they only exist in museums or such like and most people have completely forgotten how to use them. For sure our present day sci fi projections have to have similar things that to future generations would be as dated as slide rules, but we can't see what they are.
See also
Trouble With Terraforming Mars
Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
To Terraform Mars with Present Technology - Far into Realms of Magical Thinking - Opinion Piece
This is not at all an argument against humans in space, and human occupied space settlements. E.g. on the Moon seems obvious place to begin, and using materials from the asteroids in free space, then maybe the moons of Mars. And with a reason to be there, e.g. for scientific exploration, or to mine water and other resources. Or for tourism, or artistic projects.
But I don't think there is much future in trying to make Mars into a second Earth, not with present day technology or foreseeable future technology.
We can do lots of good things in space. One of the most obvious and immediate things is to search for asteroids that might hit Earth - and deflect them if necessary. This is well within our ability and for a tiny tiny fraction of the figures suggested for colonization.
For half a billion dollars for instance, we could fund the Sentinel telescope proposed by the B612 foundation. And pretty much sort out completely the issue of asteroid impacts, even the tiny ones, well within a decade of its first launch. We have already found all the 10 km or larger asteroids in near Earth space - out to Jupiter.
Rather than try to ensure that a small part of our population is able to escape from Earth, we should save Earth, the only reasonably habitable place for humans in our solar system. And not likely to change that in the near future, even centuries into the future. If that does change, then things would be so utterly different from what they are now, is hard to imagine it.
E.g. the space habitats that would feed human colonies - if you used the same technology on the Earth, at say 50 square meters of greenhouses to support each person - you could feed the entire population of the Earth using 5% of the area of the Sahara desert. And with far simpler technology - don't even need to think about oxygen generation for instance, or removing poisonous gases and dangerous microbes - just need to open the windows of the habitat for that, on Earth.
And if you can 3D print the $10 million spacesuits, you can 3D print just about anything, again you could just set up shop in the desert, scoop up some sand and rocks,and build anything you like. If you can do it in space you can surely do it on the Earth. That may be possible in the future, who knows, but I think it is too soon to start millenium long projects that rely on not yet invented technology - as - who knows if the future will still want the outcome of those projects?
In the case of a partial, unsuccessful, probably abandoned due to expense, terraformed Mars, maybe lost its water into the desert sands, maybe problematic microbes spread and colonized it, maybe byproducts dangerous to humans added to the soil or the atmosphere - I think it is extremely unlikely myself that it will seem to future generations that we have improved the solar system for them.
But if we keep to the ideas, exploring ideas and proposals for terraforming planets doesn't harm any planets - and if we work on closed systems in controlled situations, for instance habitats on the Moon or colonies in free space, built using materials from the asteroids, or in case of Mars, its moons, where you can reset and start again, and experiment with different parameters and see what happens - in that case I think what we do could potentially be useful to ourselves and also to future generations.
People sometimes talk about trying to terraform Mars as an experiment. But that's no experiment. No control. No statistics to analyse. Whatever happens could be just a fluke, a one in a trillion chance, or could be it happens to nearly all planets, but we wouldn't find out by just going ahead and seeing what happens. Not with just one planet to try it out on. That's just playing around, mucking things up to see what happens. With no clear idea for why you are doing it or what you hope to learn. More like what children may do playing as scientists. And if what you learn is that you made a mistake - what do you do then?
The main thing is not to do any major irreversible thing that affects an entire planet. Instead start smaller, where we have a chance of actually understanding what is going wrong when it inevitably does go wrong, and where we can actually do something about it, simply replace the atmosphere or the soil if problematic gases or compounds or microbes build up for instance. And can do controlled experiments. And start again and vary the parameters and see what happens. That then is real science, not just playing at science.
Why We Can't "Backup Earth" On Mars, The Moon, Or Anywhere Else In Our Solar System
There's actually far more space for colonization anyway in asteroids. A planet is the least efficient way to get living area from a given amount of matter as a sphere. Of all solid objects, the sphere has the smallest surface area for its mass. And in many ways it is far easier to mine asteroids than a planet, because of their low gravity - if you want to use the material elsewhere.
This is an observation that goes back at least as far as the 1970s when they designed all those O'Neil cylinders and Stanford Toruses.
For more on this:
Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
First there's the idea of warming up Mars. The cheapest is probably to use greenhouse gases. But though that's much easier than mirrors with an area similar to that of Mars itself, it's still pretty tough. It is only easy by comparison with other solutions.
The problem is that at present the Mars atmosphere is in an equilibrium where if more CO2 is released temporarily, it will just turn back into dry ice again at the poles. So you need a permanent on-going way to keep it in the atmosphere. That is - unless you can push the amount of CO2 up over the magic number of 10% of Earth's atmospheric pressure. If you do that you get a runaway effect.
But that involves releasing, somehow, 100,000 cubic kilometers of dry ice into the atmosphere. If that exists at all. So far we know of a deposit with 10,000 cubic kilometers. If we somehow could release all of that into the atmosphere, it wouldn't 'be enough to start a runaway greenhouse - it is an order of magnitude too little - it would just all condense back to the poles again.
We don't even know for sure if Mars has enough CO2 to reach that magic 10%. If it did, then it would then all evaporate in a runaway effect until all the CO2, however much it is, goes into the atmosphere.
But the "easier" approach is to use greenhouse gases. Instead of turning 100,000 cubic kilometers of dry ice into gas, you "only" need to mine 11 cubic kilometers of fluorite. A dramatic improvement. And what's more, it makes the tipping point lower, so you don't need to go all the way up to 10% of Earth's to start the process going.
Nevertheless - that means 257,000 times Earth's current yearly production of those gases for a century. And to power that, you need 245 half a gigawatt power stations on Mars all operating 24/7 for a century, just making greenhouse gases. And all the mining technology to supply those factories with ores, searching the planet for fluorite ores and anything rich in fluorine to return to your factories.
That is what they call the "easy way" to create a dense atmosphere on Mars.
More about that here: Why Nukes Can't Terraform Mars - Pack Less Punch Than A Comet Collision
And then remember, that CO2 is actually poisonous to humans above 1%, so even if you can get oxygen as well somehow, all that CO2 you used to warm the planet has then to be converted back into plant matter, peat, trees etc. And when you do that, of course the planet,without all that CO2, cools down again so you have to step up your production of greenhouse gases to compensate and continue that long term. Or by then you might decide it is easier to build your huge mirrors in space, with area similar to the surface area of a planet, to double the amount of sunlight reaching the Mars surface.
And you have to supply all of the nitrogen as a buffer gas. Plants aren't going to supply it as they produce oxygen, not nitrogen. You have to mine it and extract it if you can find it. Or if there isn't enough as there very well might not be, then import it from comets or the like.
And the timescale, for producing the oxygen once you have your dense CO2 atmosphere (if you get that far, and to get that far probably would take 1,000 years, if it is possible), if you look at the studies, Chris McKay estimates 100,000 years to generate enough oxygen to breath in the atmosphere- at the end of which the surface is covered in organics to a depth of many meters, taken out of the atmosphere by plants. And that is of course a huge speed up over the hundreds of millions of years it took for Earth.
But then the main thing is that Mars is not like Earth. Lower gravity, which means you need three times as much of everything by mass for the same atmospheric pressure. Your plants have to work three times harder. But it is also further from the sun. So they get only half the light they do on Earth. And it's colder, even after all that warming, it will be some time before you get to temperatures where trees can grow, even when the atmosphere is thick enough. Indeed, they reckon you'd need to continue to produce large quantities of greenhouse gases in perpetuity to keep the planet warm enough for trees.
And then on the very long time scale of millions of years - well Mars will surely lose all its water again, what little it has left that you managed to liberate with your terraforming. And the carbon dioxide probably turns into carbonates, because it has no continental drift.
So - in short, it's a fascinating idea intellectually. But - short of some really game changing ideas and technology, it is a hugely difficult task. Far harder than the science fiction writers make it out to be.
Remember they are good at writing entertaining and thought provoking stories. But their speciality is not an ability to predict the future. Sometimes they get things right but sometimes they fail hugely. E.g. all the stories about thick drifts of dust on the Moon, then when we got there, the dust is only thick enough for a footprint. No chance at all of astronauts sinking into it out of sight. Right up until a few years before the Apollo landing, sci fi writers were writing stories about these dust drifts on the Moon. Arthur C. Clarke's famous, very hard sci. fi. A Fall of Moondust was published eight years before Apollo 11 - he has an entire lunar cruiser disappear into a lunar dust drift right out of sight without a visible trace on the surface.
Or stories about far future astronauts using slide rules to help pilot faster than light spaceships - for instance Robert Heinliem's "Slip-stick Libby" is a dab hand at slide rules, how he got his name, and in Methuselah's Children he uses one to make last minute adjustments to his novel faster than light space drive.
It was published in 1958 but in the 1960s when I was a young teenager, such stories didn't seem anachronistic, but rather - the slide rule was a mark of hard sci. fi.
Now they only exist in museums or such like and most people have completely forgotten how to use them. For sure our present day sci fi projections have to have similar things that to future generations would be as dated as slide rules, but we can't see what they are.
See also
Trouble With Terraforming Mars
Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
To Terraform Mars with Present Technology - Far into Realms of Magical Thinking - Opinion Piece
This is not at all an argument against humans in space, and human occupied space settlements. E.g. on the Moon seems obvious place to begin, and using materials from the asteroids in free space, then maybe the moons of Mars. And with a reason to be there, e.g. for scientific exploration, or to mine water and other resources. Or for tourism, or artistic projects.
But I don't think there is much future in trying to make Mars into a second Earth, not with present day technology or foreseeable future technology.
We can do lots of good things in space. One of the most obvious and immediate things is to search for asteroids that might hit Earth - and deflect them if necessary. This is well within our ability and for a tiny tiny fraction of the figures suggested for colonization.
For half a billion dollars for instance, we could fund the Sentinel telescope proposed by the B612 foundation. And pretty much sort out completely the issue of asteroid impacts, even the tiny ones, well within a decade of its first launch. We have already found all the 10 km or larger asteroids in near Earth space - out to Jupiter.
Rather than try to ensure that a small part of our population is able to escape from Earth, we should save Earth, the only reasonably habitable place for humans in our solar system. And not likely to change that in the near future, even centuries into the future. If that does change, then things would be so utterly different from what they are now, is hard to imagine it.
E.g. the space habitats that would feed human colonies - if you used the same technology on the Earth, at say 50 square meters of greenhouses to support each person - you could feed the entire population of the Earth using 5% of the area of the Sahara desert. And with far simpler technology - don't even need to think about oxygen generation for instance, or removing poisonous gases and dangerous microbes - just need to open the windows of the habitat for that, on Earth.
And if you can 3D print the $10 million spacesuits, you can 3D print just about anything, again you could just set up shop in the desert, scoop up some sand and rocks,and build anything you like. If you can do it in space you can surely do it on the Earth. That may be possible in the future, who knows, but I think it is too soon to start millenium long projects that rely on not yet invented technology - as - who knows if the future will still want the outcome of those projects?
In the case of a partial, unsuccessful, probably abandoned due to expense, terraformed Mars, maybe lost its water into the desert sands, maybe problematic microbes spread and colonized it, maybe byproducts dangerous to humans added to the soil or the atmosphere - I think it is extremely unlikely myself that it will seem to future generations that we have improved the solar system for them.
But if we keep to the ideas, exploring ideas and proposals for terraforming planets doesn't harm any planets - and if we work on closed systems in controlled situations, for instance habitats on the Moon or colonies in free space, built using materials from the asteroids, or in case of Mars, its moons, where you can reset and start again, and experiment with different parameters and see what happens - in that case I think what we do could potentially be useful to ourselves and also to future generations.
People sometimes talk about trying to terraform Mars as an experiment. But that's no experiment. No control. No statistics to analyse. Whatever happens could be just a fluke, a one in a trillion chance, or could be it happens to nearly all planets, but we wouldn't find out by just going ahead and seeing what happens. Not with just one planet to try it out on. That's just playing around, mucking things up to see what happens. With no clear idea for why you are doing it or what you hope to learn. More like what children may do playing as scientists. And if what you learn is that you made a mistake - what do you do then?
The main thing is not to do any major irreversible thing that affects an entire planet. Instead start smaller, where we have a chance of actually understanding what is going wrong when it inevitably does go wrong, and where we can actually do something about it, simply replace the atmosphere or the soil if problematic gases or compounds or microbes build up for instance. And can do controlled experiments. And start again and vary the parameters and see what happens. That then is real science, not just playing at science.
Why We Can't "Backup Earth" On Mars, The Moon, Or Anywhere Else In Our Solar System
There's actually far more space for colonization anyway in asteroids. A planet is the least efficient way to get living area from a given amount of matter as a sphere. Of all solid objects, the sphere has the smallest surface area for its mass. And in many ways it is far easier to mine asteroids than a planet, because of their low gravity - if you want to use the material elsewhere.
This is an observation that goes back at least as far as the 1970s when they designed all those O'Neil cylinders and Stanford Toruses.
"The next question the students considered was how much land area could you build in such habitats, using the material resources of the moon or the asteroids, which may be readily available in space? What are the limits to growth?
"The first answers they came up with indicated there was more than a thousand times the land area of Earth as the potential room for expansion. They concluded that the surface of a planet was not the best place for a technical civilization. The best places looked like new, artificial bodies in space, or inside-out planets."
Colonies in Space: Chapter 2
For more on this:
Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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