Who cares how much carbon dioxide is on Mars?

Thursday, August 30th, 2018

The whole argument over how much carbon dioxide is on Mars now is totally irrelevant, since we need to import far, far more nitrogen to terraform the planet:

The surface pressure on Mars now averages about 0.6 percent of our own sea level pressure, or about 0.087 psi (600 pascals), and is thus a “physiological vacuum”. This means the pressure is less than a tenth of the “Armstrong Limit” of about 0.9 psi (6,200 pascals) where blood boils and far below what is needed to survive even with pure oxygen. You would need to wear a pressure suit to survive on the surface, just like on the Moon. Fortunately, though chilly, the temperatures on Mars are much milder than those on the Moon.

In addition, the surface of Mars is exposed to about 250 millisieverts (mSv) per Earth year of solar and galactic (cosmic) radiation, composed partly of dangerous high-speed atomic nuclei that can leave a trail of dead brain cells behind. Due to these particles, cosmic radiation is more dangerous than “regular” radiation. Crews and early civilian settlers would need to live underground in heavily shielded, pressurized habitat buildings to prevent the cosmic ray nuclei from reaching them. For reference, you would experience some radiation sickness if you got a dose of 1000 mSv all at once. In interplanetary space, you would get about 657 mSv per year without shielding, but on Mars, the planet itself blocks half of the radiation and the thin atmosphere absorbs another 20 percent of what remains. At this lower but constant rate, you would not get sick but there would be cumulative cell damage and a slow increase in cancer risk. On Earth, at sea level, we have in effect a layer of air equivalent in mass to 10.3 meters of water over our heads, which absorbs virtually all of the dangerous high-energy particles. On Mars, that layer is equivalent to about 20 centimeters of water, barely enough to shield anyone from a dangerous solar “proton storm” radiation outburst.

So there are three main reasons we need significant air pressure on Mars: to remove the need for pressure suits when working outside (and so that we would no longer need to live in pressurized habitats), to allow water to exist as a liquid on the surface, and to block the ubiquitous cosmic radiation so that buildings can be right on the surface and so that people can work on the surface without being irradiated. We can look at this issue from two points of view: radiation blocking mass and air pressure. So how much air mass and pressure do we really need?

From the radiation perspective, this is primarily a matter of sheer mass. On Earth at sea level, we have enough air over our heads so that only a tiny fraction of the natural background radiation most people get per year, totaling 3 to 6 mSv, is from space. To duplicate that very good level of protection on Mars requires a comparable amount of air mass (10.3 metric tons) over every square meter of Mars surface, ignoring the great altitude differences. Multiply this by the number of square meters of Mars surface and you get the required air mass: 1.493 trillion metric tons. This amount would create about 6.14 psi of air pressure or about 0.42 of Earth sea level pressure. More importantly, essentially all of the dangerous cosmic radiation from space would be blocked. This compares to the paltry 25 trillion metric tons of air currently in place at Mars, almost all of it CO2.

Some may note that for the same air column mass (the mass of air over a given surface area), we are not getting as much air pressure as we do on Earth. With Mars lower gravity, about 38% of Earths, it takes more air mass per square meter than it does on Earth to produce the same amount of pressure. So with the radiation threat now (theoretically) dealt with, how much air pressure do we need and what kind?

Right now, the air you are breathing is about 78 percent nitrogen and only about 21 percent oxygen. Carbon dioxide is a trace gas, at only 0.04 percent. You actually breathe 25 times more argon than carbon dioxide. If you are old enough, or are a space history buff, you may remember the Apollo 1 fire. The first Apollo spacecraft being prepared to be launched with a crew had about 16 psi of pure oxygen inside it during a pre-launch test, and all of the metal and plastic surfaces were saturated with oxygen. The capsule interior was like a fire bomb waiting for one tiny spark. The three astronauts were quickly asphyxiated by smoke within a minute of that spark and most of the interior of the capsule was incinerated. This horrific accident illustrates how dangerous high levels of oxygen are.

So future colonists would have little use for an atmosphere of almost all carbon dioxide, and they would not want an atmosphere mostly of oxygen due to the huge fire risk it would create. It turns out that the oxygen in any future nitrogen-oxygen atmosphere should be less than 50 percent of the total air pressure, but with the 42 percent pressure described above, we would still need a future 50-50 oxygen and nitrogen mix. (The amount of nitrogen delivered should be related to the future oxygen component.) So if we increase the air column mass to about 12.3 metric tons over each meter of surface, we get almost exactly half sea level pressure, or about 7.35 psi. To create this half-atmosphere of pressure (almost all of nitrogen) we need to add 1,784 trillion tons of nitrogen. However, this is equivalent to an altitude on Earth of about 5,200 meters, the altitude of the highest community on Earth in the Andes.

We assume, once we have a half-atmosphere of pressure, early settlers would be using oxygen helmets when working outside, and living inside slightly pressurized habitats, which could then be on the surface, with a nitrogen-oxygen mix. In addition, those in charge of the terraforming process would want to find ways to slowly add oxygen to the atmosphere, such as using the oxygen in some of the carbon dioxide and the existing water on Mars. This may take a long time, but adding oxygen will also add to the atmospheric pressure. Eventually, perhaps after centuries, there would be enough oxygen to breath and green plants could grow outside, but not so much as to be dangerous. A reasonable mix at about 10 psi would obviously be 70 percent nitrogen and 30 oxygen oxygen, providing the needed 3 psi of oxygen. This would be similar to being at about 3,000 meters on Earth, which the majority of people can obviously tolerate. For example, the town of Leadville, Colorado, is at an altitude of 3,100 meters. This is why we want the nitrogen in place first as it is a non-reactive gas.

Wait, I have a question:

Now, of course, many people will wonder where do we get all of these trillions of tons of nitrogen to import onto Mars. The planet has very little of it: just a few percent of what is needed, as most of it was lost during the last 3.5 billion years. However, It turns out that the outer solar system has huge amounts of nitrogen, both as a gas, such as on Titan, and as a semi-solid slush or ice on Pluto, Triton, and very probably the other large Kuiper Belt dwarf planets. Small asteroids would not have significant amounts of nitrogen as their gravity would have been too low to hold an atmosphere. We should be able to mine some of this nitrogen and move it to Mars where it can help support life. The current atmospheric loss rate from Mars would be very low.

Right now, it is true we have no means of moving the nitrogen, but chances are, with the new private investments in fusion power, that we will have it before we are ready to start terraforming. Fusion rocket powered tugs would only need to thrust for a few days to a couple weeks to send huge loads of nitrogen—as much as 100 million tons in each load—into the inner solar system at low speeds and carefully intersect the atmosphere of Mars. Ten such loads would deliver a billion tons of nitrogen, as much mass as a cubic kilometer of water, and 10,000 loads would deliver a full trillion tons.

The image at the top of this article shows a load of 100,000 chunks of nitrogen (shown as cubes but they could be in huge plastic bags.) Each chunk is about 10 meters across and weighs about 1,000 tons. By aiming these large loads of nitrogen ice so that they come in exactly horizontally at the high atmosphere of Mars over the desired areas, instead of impacting on Mars surface, there are no craters formed and all of the nitrogen is turned into gas and added to the atmosphere over an entry path of hundreds of kilometers. Very large amounts of heat, but no dangerous radiation, are created by these entries, which would occur many times a day and go on for over 100 years.

The entries could be targeted over the ice caps or glaciers and would easily melt them totally, as each entry produces as much radiant heat as a hydrogen bomb but with no dangerous radiation. Thus, the ice cap melting can be done by these repeated entry events, instead of a few, very dangerous cratering events. The fusion tugs back away from their loads before entry and head back to the outer solar system at high speed since they now have no load. Climatologists may have to hurry to get valuable ice cores of all the ice cap areas before they are melted to form a new, but initially shallow, Boreal Ocean and other bodies of water.

Easy-peasy then!


  1. Kirk says:

    Before going to all the trouble of dragging an atmosphere and ocean to Mars, we might want to spend some time adding mass, so that those things don’t evaporate again…

    Seem to remember that there is a bunch of mass in small pieces sitting out near the Mars orbit, anyway. Take some time, stop it in slowly while we exploit the asteroids, and we should have collected enough to tip Mars over the mass limit to make it easier to keep the biome we want to grow…

    I mean, if you are gonna do planetary-scale engineering, do it right.

  2. Harry Jones says:

    Coming in at well above escape velocity, and mingling momentum with the pre-existing volatiles. Will there be a net gain or will this just propel the existing atmosphere and polar caps into space?

  3. Sam J. says:

    Better to build space habitats in the first place. Less mass needed and it would spread the risk. Bound to be cheaper.

  4. Kirk says:

    @ Sam J.,

    The whole idea of permanent space habitats has always struck me as a little, y’know… Nuts.

    First, and biggest problem? The scale and the resultant fragility from being on a small scale. You don’t have to worry about a meteorite strike taking out a planetary atmosphere, but you sure as hell do with a habitat. Collisions, damage, radiation flares… All that crap militates against habitats as permanent residences. A planet is redundant, and a fairly robust proposition on the normal time frames humans are worried about. A habitat? Yeesh… Especially some of the ones I’ve seen proposed, with literal cubic miles of internal unbaffled space to allow for a feeling of real living space.

    My suspicion is that most people who live in space are going to be extremely uncomfortable with that sort of thing–You experience one blow-out loss of pressure on something that big, and you’re never going to be comfortable living that way again. What I expect is that there are going to be habitats, but they’re going to be relatively tiny affairs, heavily armored, with multiply-redundant systems to maintain atmosphere. Great big open-air spaces are going to be causes for extreme paranoia and discomfort, especially for survivors of any real failure. At least, with current tech–Give us force-fields and artificial gravity, and it may not be so bad.

    Social ramifications of space habitats are also going to be… Interesting. You think the Japanese are conformist and socially rigid, wait until you see the long-term social consequences of living in the high-risk environment of a space habitat… I would be surprised if that doesn’t generate a bunch of major social differences in very short order, and I would suspect that low-trust societies like the Arabs aren’t going to be very successful in that environment. You think it’s bad when they can’t even keep their own city spaces clean on-planet, translate that over into a space habitat, where the consequences of a failure to police the commons will be deadly…

  5. Wang Wei Lin says:

    Mars doesn’t have a magnetic field to buffer the solar wind. I doubt additions to the atmosphere would outpace losses to solar wind.

  6. Sam J. says:

    Well if a planet buster takes out Earth it’s all over for us but if it takes out one habitat then it’s just one. A tragedy but not…the end. All the bad feelings you have about habitats are true but I suspect that people raised on one would get used to it. Mars would take a LOT of maintenance and demand a high energy, high level of industry to survive. Much like the habitats. Mars probably much, much more in terms of resources. If we’re going to survive for the next ten thousand years we will need them. As for asteroids a small radar system could warn you.[We should have a major system looking for planet busters right now but...we don't.]

    I wonder what it would take to build a magnetosphere on Mars? Have you ever heard of statities? These hover over the north or south pole of a planet. It balances the gravity of the planet and the solar wind hitting the very large statatite. It has to be far out to work. What if it used all the solar power to make an electric field??? Maybe crazy but not much more crazy than terraforming Mars. I wonder if space has enough particles to make a circuit between to statities????

  7. Bob Sykes says:

    On the fun side, some NASA people have proposed lacing the Martian atmosphere with super green house gases like perfluorocarbons, enough to melt the CO2 and maybe even the water:


    Since we are having trouble keeping the ISS up, we had better work some more on our game.

    Just when does the US get its manned space program back? Even China has one.

  8. Jack says:


    It’s a reasonable question, but I’m afraid the answer is never — NASA has been thoroughly unmanned.

  9. Ritchie says:

    If you want to make Mars anything more than a mountain cottage, it’s going to need a circulating metallic core and plate tectonics. You know what it takes to do that? A planetary sized microwave oven. Start running numbers.

  10. Cererean says:

    “Mars doesn’t have a magnetic field to buffer the solar wind. I doubt additions to the atmosphere would outpace losses to solar wind.”

    According to NASA, the loss to the solar wind is significantly less than the gain from outgassing (as I calculate here – http://newmars.com/forums/viewtopic.php?pid=148825#p148825). Which means that something else is keeping the atmosphere at it’s low level. It’s probably no accident that it hovers around the triple point of water.

    We don’t need to make the atmosphere Earth-like for it to be very useful. A ~100mb CO2 atmosphere would provide much more radiation shielding and, importantly, enable farming to occur in lightweight unpressurized polytunnels. Far cheaper than the greenhouses we’d need with today’s Mars – or the complex arrangements we’d need for in-space colonies. At that point in terraforming, there should be some liquid water as well, and the possibility of genetically engineered plants growing on the surface and putting out oxygen which can be easily distilled from the atmosphere.

  11. Mike says:

    Just a couple of thoughts:

    1) Would it be possible to use one or more other gases instead of Nitrogen?

    2) Even if an atmosphere is created, wouldnt the lack of a substantial moon (phobos and demios arent big) mean that the weather system would be extreme. No moon means no tides means no circulation of water.

    3) Why has no one thought of Venus as a potential planet for terraforming? Or is removing/modifyog an atmosphere more problematic thsn creating one?

  12. Isegoria says:

    Colonizing Venus may be easier than colonizing Mars, but it would involve floating cities, in an acidic atmosphere.

  13. Sam J. says:

    Cererean says,“Mars doesn’t have a magnetic field to buffer the solar wind. I doubt additions to the atmosphere would outpace losses to solar wind.”

    I say there’s little to no difference to being forced to live in tunnels on the Moon or Mars and living in a Habitat in space. The Habitat would seem more roomy. To bad we don’t have some of that “Ring World” stuff to make Habitats out of.

  14. Mike says:

    Thanks for the links. Floating cities, or at least small habitation ships (blimps?) do seem like a bizarrely feasable idea. Not on a city scale but certainly for smaller scientific operations. Something along the scale of the International Space Station.

  15. Kirk says:

    At this point in the game, I think there is limited real value in speculation about precise techniques for creating off-world human habitats. While I’m sure that it is possible, the questions of precisely how it can be done are still highly speculative. The questions of just what it is that we’d need to recreate aren’t even really known, either–How much of human biology relies on things we don’t even think about, like environmental signalling and magnetic fields? What are the long-term effects, if any, on things like human reproduction? What cues from the environment are we going to be missing?

    I have the opinion that there’s going to be a lot more to this whole question than we’re really even aware of, and it may well be that we’re not going to be able to do it in any large-scale or effective manner, without exponential increase in both our knowledge and capabilities.

    Hell, I wouldn’t necessarily rule out that the whole thing is going to require transfer of consciousness to electro-mechanical surrogates, either. We may only get off of Mother Earth as disembodied electronic ghosts.

  16. Cererean says:

    “I say there’s little to no difference to being forced to live in tunnels on the Moon or Mars and living in a Habitat in space. The Habitat would seem more roomy.” – Sam J

    Not really. In space, you need to provide a lot more radiation shielding and spin the habitat for gravity. Mars as it is today is an easier place to build such habitats, particularly given the abundance of different resources available. A partially terraformed Mars, where farming can take place in unpressurised polytunnels, would be a lot easier than that. Most land humans use is used for growing plants, whether to eat directly or to feed to livestock. It’s far more expensive to create farmland in space than it would be on a Mars with a ~100mb CO2 atmosphere.

  17. Kirk says:


    I think that trying to speculate about what’s going to be the “easier/more likely” path to colonizing off-Earth living spaces is extremely premature. We don’t even know what we don’t know, to be honest.

    Yeah, artificial habitats might not be economical, but what about the problems with moon dust and the Martian perchlorate deposits? Keeping that crap out of the environments we try to build on either the Moon or Mars may actually be unaffordable, in terms of long-term viability. If you think silicosis is hard to deal with on Earth, then try it in a low-gravity vacuum environment. The early settlers are going to have a lot of very complicated issues to deal with, many of which are not even foreseeable to us at this time.

    The other thing to consider in all of this is the psychological aspect–If you know guys and girls who do things like sailing small craft on long ocean voyages, you’ll note a certain difference between them and their land-borne compatriots. The ones who actually survived that sort of thing, back before satnav and easy access to rescue?

    All of the ones I’ve known were anally-retentive detail freaks with extreme OCD for things like “Did I shut that hatch? Is the porthole open…? Did I buy the flour at the last stop…?”.

    Friend of the family did a bunch of solo cruises back during the 1960s, one of which was a cross-Pacific voyage. I don’t know if the guy I knew did those voyages because he had those traits, or if he developed them sailing alone, but… He had those tics, for life. Dude could not go to a store and just buy something–He had to have a list, and a well-thought out reason. No plan? No action… Zero spontaneity.

    You also find that same sort of psychological effect in guys who do cave diving and other such sports. From this, I think we can reliably predict that anyone who lives in an unforgiving environment like deep space is going to exhibit similar traits, and that the societies made up of people like that are going to be… Different. Very, very different. Japanese may do well, given that they are already used to the high-cohesion and socially conformist requirements that living in a deep-space environment will likely have.

    Arabs? LOL… Islam in general? Any relatively primitive and low-social trust society? Ain’t going to happen. All it’s going to take is one guy in the habitat getting greedy and saying “Screw my buddy…”, and everyone there suffers or dies. People prone to that behavior are probably going to wind up going straight out an airlock for things like failing to recharge an emergency air supply after using it. Many generations of this, and you’re going to have a very different culture and society. It may even produce identifiable biological effects stemming from selection for specific behavior sets.

  18. Sam J. says:

    Cererean says,”Not really.”

    Sam says, with a mischievous twinkle in his eye,”Yes really.” :)

    “…In space, you need to provide a lot more radiation shielding and spin the habitat for gravity Mars as it is today is an easier place to build such habitats, …”

    Mars has little atmosphere for shielding so…you have to dig up habitat anyways. What difference if what you dig up you dig up from the Moon, on Mars or an asteroid??? Still have to dig and crush it. Move it.

    “…particularly given the abundance of different resources available…”

    No resources in Space???? Where you going to get your terraforming atmosphere??? Massive resources in space on low gravity floating rocks of any sort you want.

    “…It’s far more expensive to create farmland in space than it would be on a Mars with a ~100mb CO2 atmosphere…”

    Not seeing it. Mars is damn near a vacuum as far as unsuited humans are concerned. Any attempt to rehab the whole planet would take an extraordinary amount of material and energy. Instead of spreading it out on the “thin” surface of a planet you could take the exact same material and make mega earth surface areas in free floating multiple habitats. The whole reason for moving to space, in my opinion, is to have a civilization back up to the Earth if it gets whacked by a big enough rock, solar flare, close by supernova, etc and use the massive resources in space.

    The big failure of Mars is it has a gravity field. A total waste. Anything going up or down must use energy and materials to no end at all. Spinning a habitat cost…next to nothing. The energy required for habitats could be far, far less. The delta V from the asteroid belt and the Moon is not that great. There’s a lot of work already done on using Moon material and mass drivers to launch it to where it’s needed. It’s so much cheaper to free float habitats in space that Mars habitats are not even in the same ball park.

    Solar power would be way cheaper in space. At Mars all that damn dust and supports and way less sunlight means you really should use nuclear power. Well if you’re going to that you can still do it cheaper in space. Mars is a high gravity suck hole.

    Look I like planets but in actuality we’re talking about energy cost and what it takes to move humans into space. If it cost too much or takes too much up front money it will never happen. Maybe Mars will be terraformed some day but I bet it won’t. I would bet it would be dismantled for logic gates that humans, or the silicon life that overthrows us, needs before so much as one load of gas is sent there. I mean a planet???. Silicon life needs no damn planet and those that refuse silicon transcendence will just stay on Earth like the Amish.




  19. Sam J. says:

    Probably no one will see this but I ran across a link to a particular type habitat that I wanted to link but couldn’t find earlier.

    “Long-term colonization of the solar system with 290,000 square feet per person”

    That’s a lot of room.

    “…A 5 km settlement radius corresponds roughly to the sweet design spot where earthlike radiation shielding is produced for free by the required structural mass…”


    Here’s another good one.


    Here’s a link describing super cheap material launch from the Moon with rail guns to Mars. Could be to Earth orbit also.

    I’ll add that with a solar concentration mirror and some separation of lunar materials we could build 3D parts out of Moon dust then launched. Large things could be launched as long as you got the center of gravity right. Maybe with slower acceleration. All this stuff could be built with a solar powered remote controlled rover with arms and manipulators. Machine tools could be built from scratch. The key is to take your time and build from scratch. I wonder how you could build amplifiers, switches or semiconductors from lunar soil? Surely must be a way. Maybe use magnetic amplifiers instead of transistors or CMOS type devices.

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