No, that's nowhere near big enough. That's about 4,000 cubic kilometers. You need 1.4 million cubic kilometers. Equivalent of a ten meter depth of dry ice over the entire surface of Mars (surface area 144 million square kilometers). About 350 of your dry ice comets.
If Mars already has this ten meters thickness of dry ice, then you can manage it by adding just one extra meter thickness - that's 140,000 cubic kilometers. Or about 35 of your ten kilometer diameter dry ice comets.
That then would trigger a runaway greenhouse effect that would cause the rest of the dry ice to evaporate as well.
But - so far we only know of the equivalent of a little over one meter average thickness of dry ice averaged over the surface of Mars. That's enough so that as its axis tilts it may sometimes have 2% of Earth's atmosphere enough for liquid water to be stable quite extensively - but not enough for a runaway greenhouse. It is not impossible that it has reserves with the equivalent of the other nine meters of dry ice underground, some think it might have a lot of dry ice coating the deep subsurface soil - but we don't have any evidence at present that it is there either.
So you might well need to add the full 1.4 million. I.e. the full three hundred and fifty of your ten kilometer diameter comets.
Bear in mind also that CO2 is poisonous to humans at 1% of the atmosphere or above. Even if supplied with oxygen, you also need to keep out the CO2. So an atmosphere of CO2 only is only habitable for plants.
Also - if you want oxygen - plants can't do it, not quickly. Trees when they decay return all the carbon back to the atmosphere. To convert significant amounts of that CO2 to oxygen, you have to take many hundreds of cubic kilometers of carbon out of the atmosphere permanently - cover the surface of Mars with organics to depths of meters. (for, say, 21% of oxygen by mass, you'd need to extract organics to a depth of more than two meters over the entire planet).
Then as well as that, it turns out that Mars can't keep itself warm enough for trees, even with an Earth density CO2 atmosphere, because it is too far from the sun for that.
So you would also need greenhouse gases or space mirrors to keep it warm. It is a bit of a mystery how the early Mars was warm enough for oceans, if it was, as seems so - perhaps the oceans were frozen over for much of the time or some form of natural super powerful greenhouse gases.
And even more so you need to keep it warm into the indefinite future by artificial means if you ever manage to create an Earth-like non CO2 atmosphere there.
Why Nukes Can't Terraform Mars - Pack Less Punch Than A Comet Collision
But that is just the start of your problems for terraforming Mars.
It's nowhere as simple as some science fiction stories make it out to be
Trouble With Terraforming Mars
It's a fun intellectual idea. And they have come up with some neat ideas about how to do it. But we are a very long way from understanding how you'd do it in practice, or if it is possible at all in the case of Mars.
If Mars already has this ten meters thickness of dry ice, then you can manage it by adding just one extra meter thickness - that's 140,000 cubic kilometers. Or about 35 of your ten kilometer diameter dry ice comets.
That then would trigger a runaway greenhouse effect that would cause the rest of the dry ice to evaporate as well.
But - so far we only know of the equivalent of a little over one meter average thickness of dry ice averaged over the surface of Mars. That's enough so that as its axis tilts it may sometimes have 2% of Earth's atmosphere enough for liquid water to be stable quite extensively - but not enough for a runaway greenhouse. It is not impossible that it has reserves with the equivalent of the other nine meters of dry ice underground, some think it might have a lot of dry ice coating the deep subsurface soil - but we don't have any evidence at present that it is there either.
So you might well need to add the full 1.4 million. I.e. the full three hundred and fifty of your ten kilometer diameter comets.
Bear in mind also that CO2 is poisonous to humans at 1% of the atmosphere or above. Even if supplied with oxygen, you also need to keep out the CO2. So an atmosphere of CO2 only is only habitable for plants.
Also - if you want oxygen - plants can't do it, not quickly. Trees when they decay return all the carbon back to the atmosphere. To convert significant amounts of that CO2 to oxygen, you have to take many hundreds of cubic kilometers of carbon out of the atmosphere permanently - cover the surface of Mars with organics to depths of meters. (for, say, 21% of oxygen by mass, you'd need to extract organics to a depth of more than two meters over the entire planet).
Then as well as that, it turns out that Mars can't keep itself warm enough for trees, even with an Earth density CO2 atmosphere, because it is too far from the sun for that.
So you would also need greenhouse gases or space mirrors to keep it warm. It is a bit of a mystery how the early Mars was warm enough for oceans, if it was, as seems so - perhaps the oceans were frozen over for much of the time or some form of natural super powerful greenhouse gases.
And even more so you need to keep it warm into the indefinite future by artificial means if you ever manage to create an Earth-like non CO2 atmosphere there.
Why Nukes Can't Terraform Mars - Pack Less Punch Than A Comet Collision
But that is just the start of your problems for terraforming Mars.
It's nowhere as simple as some science fiction stories make it out to be
Trouble With Terraforming Mars
It's a fun intellectual idea. And they have come up with some neat ideas about how to do it. But we are a very long way from understanding how you'd do it in practice, or if it is possible at all in the case of Mars.
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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