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CONTEXT and INTRODUCTION

Humans establish colonies on Mars with slightly more advanced technology than we have today. The Martian colonists lose all contact with Earth. Over centuries, the Martian colonists develop a distinct culture (w/ practices, religion, language, etc). My story takes place in this culture. A fundamental defining element of this culture is technophobia / technological deterioration (for various irrelevant reasons).

I have two issues pertaining to the atmosphere of Mars that prevent human habitation. Firstly, the chemical composition of the Martian atmosphere is unsuitable: low O$_2$ and high CO$_2$. Secondly, the atmospheric pressure of Mars averages a mere 600 pascals which is unsuitable for human habitation. Somehow, my Martians need to be able to inhabit Mars and survive (but not thrive).

However, as aforementioned, the Martian populace are technophobic. Their technology is rather primitive, technological development is almost non-existent and technology from the very first colonies is irreproducible and/or lost. As such, terraforming is out of the question. As are more advanced technologies, such as spacesuits and pressurized habitats.

THE “OXYGEN RADIATION ZONE”

Therefore, I am trying to devise a theoretical natural formation that provides the Martians with a localised habitable area.

Currently, this natural formation is an unpressurized ‘Oxygen Radiation Zone’. Oxygen is released from underground in a volume significant enough to provide a local area with suitable atmospheric pressure and composition for survival (but not ‘thrive-al’). I have included a diagram to better describe this ‘Oxygen Radiation Zone’. Please consider the diagram from a birds-eye-view.

Oxygen Radiation Zone Diagram Oxygen Radiation Zone Diagram

  1. ‘Oxygen leak’: where oxygen from underground is released in significant volume.

  2. ‘Livable area’: the area inside the black circle where atmospheric pressure and composition are suitable for human survival. Cities are built in a ring-like fashion, radiating from the ‘oxygen leak’.

  3. The extent of the ‘livable area’.

  4. ‘Transition area’: where atmospheric composition and pressure are gradually returning to the Martian normal. This area is unlivable.

  5. The extent of the ‘transition area’: where atmospheric composition and pressure become indistinguishable from the Martian normal.

  6. Martian normal.

NOTE: In the diagram, the areas are well-defined, but I imagine the whole thing to be a pressure gradient, from the high-pressure ‘oxygen leak’ (1) to the low-pressure Martian normal (6).

COMPLICATION: Winds

My understanding of pressure systems is quite basic. From the research that I have done, air moves from an area of high-pressure to an area of low-pressure resulting in the generation of wind. The intensity of these winds is determined by the pressure gradient. Therefore the pressure gradient from (1) to (6) would have to be gradual to avoid unwanted strong winds. Is this correct? If so, would this gradual pressure gradient be extremely large in area?

COMPLICATION: Oxygen escape

I know that oxygen molecules would escape from this ‘Oxygen Radiation Zone’, because of low gravity on Mars. However, the underground oxygen source that I have theorized is renewable and therefore I believe that this complication is mitigated, as long as influx of oxygen molecules matches efflux of oxygen molecules.

COMPLICATION: Dust storms and dust devils

Mars is asymmetrically heated in different seasons, which produces a mean overturning circulation called a Hadley cell. In short, this Hadley cell is responsible for the production of global-scale dust storms (among other things). Dust devils are localized convection cells that can reach 1 to 2 km at the bases and may be as tall as 8 to 10 km. How would these dust storms and devils interact with my ‘Oxygen Radiation Zone’? Would they be diverted around it?

CONCLUSION and QUESTIONS

I understand that this ‘Oxygen Radiation Zone’ is not scientifically accurate to the minute detail.

Is my design somewhat scientifically feasible? Are there any major complications that I may need to consider?

This is a whopper of a question. Thank you for taking the time to read it and provide me with feedback.

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    $\begingroup$ If you release a gas in a vacuum (or, in the specific case, a volume of very low pressure), it will expand to fill the volume; when this expansion occurs over large areas it's called wind. Humans can live in an atmosphere of pure oxygen at about 0.15 to 0.2 atm, whereas the general atmosphere of Mars is at about 0.06 atm. This pressure differential of about 0.1 to 0.14 atm will give you typhoon-force winds blowing radially. You need to generate enough oxygen to sustain a continuously blowing typhoon! Any storms and dust-devils outside the typhoon ring are much to weak to matter. $\endgroup$
    – AlexP
    Feb 15, 2018 at 2:40
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    $\begingroup$ Simply, no. A perpetually renewable source of oxygen to compensate for molecules leaving the atmosphere is by definition impossible. What would the source be? Where would this source have come from. What would happen to the ground as the source loses both mass and volume? $\endgroup$
    – nzaman
    Feb 15, 2018 at 2:43
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    $\begingroup$ @AlexP Actually (pedant alert!) free expansion of a gas does no work. So, while the mass flow will be large, there will be no work done, so no 'force' of expanding gasses felt. Trust me, I did two hours of edits on my answer before I got the science correct. $\endgroup$
    – kingledion
    Feb 15, 2018 at 4:27
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    $\begingroup$ @kingledion: Double pedant alert: Joule expansion does not do work outside the system. The best example is a rocket engine, which works by allowing high pressure gas to escape into the surrounding vacuum, thus pushing the rocket. If we consider the system to be the rocket plus all the empty space around it then no work is done; but we are usually interested only in the rocket. $\endgroup$
    – AlexP
    Feb 15, 2018 at 5:33
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    $\begingroup$ Too lazy to do the math (so no answer) but the only option I see is that your people live in a deep depression. In the same way as pressure goes down with altitude it will go up with depth. With deep enough "hole" you could have usable pressure while in equilibrium with rest of the atmosphere. This also increases local temperatures and provides a convenient excuse why oxygen is released in that convenient location. $\endgroup$
    – Ville Niemi
    Feb 15, 2018 at 6:21

3 Answers 3

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Not feasible; requires too much oxygen

Free expansion is a process where a gas expands into a vacuum. Your Martian atmosphere is not quite a vacuum, but it is close enough compared to the air pressure required for your people to breathe.

The math behind free expansion is

$$\frac{P_i}{P_f} = \frac{V_f}{V_i},$$

the ratio of volume increase is the inverse of the pressure decrease. We can model the expansion of the gas as a hemisphere (ignoring gravity, oops!). The volume as a function of radius is $$\frac{2}{3}\pi r^3.$$

The free expansion of gas into a vacuum is going to proceed at the average speed of the particles. The mean speed of the particles is based on the Maxwell-Boltzmann distribution and is $$\mu = 2\sqrt{\frac{2kT}{\pi m}},$$ where $k$ is the Boltzmann constant ($1.38\times10^{-23}$ J/K), $T$ is the temperature (lets use 210 K as average surface temperature), and $m$ is the mass of an oxygen molecule ($2.66\times10^{-23}$ kg). Plugging those numbers in we get an expansion speed of 17 m/s. Every second, the radius of expanding oxygen will increase by 17 meters.

As the radius of oxygen increases, the volume of oxygen will increase by the cube of that number, or a factor of almost 5000. We see from free expansion that the pressure drop is the inverse of the increase in volume, so pressure will drop by a factor of 5000 from a point 1 meter away to a point 17 meters away.

But this is just for the first second. Let us set a constant oxygen leak value. The Amazon river discharges 200,000 m$^3$ per second, lets use that value. We must convert this to a number of molecules, since the density of this gas will be variable. 200,000 m$^3$ of oxygen at STP would be about $8.9\times10^{6}$ mol.

Using the free expansion formula and the ideal gas law, we can calculate an average pressure for each meter wide hemispherical slice of the expanding gas.The pressure at 15 meters away will be 11 bars, for example.

Lets say that the breathable range is from 0.3 bar (this is the pressure used by the Gemini spacecraft as 100 % oxygen) to 0.1 bar (this is the partial pressure of oxygen at about 4000 meters). The distance for 0.3 bar is 45 meters, the distance for 0.1 bar is 65 meters.

Conclusion

There is a 20 meter wide safe zone you could operate in, 45 meters from the oxygen source. However, this is with an Amazonian level of gas input to the atmosphere. Adding 285000 kg of gas per second is not reasonable. Lets say we drop the numbers of 285 kg per second. Now, instead of the range from 45 to 65 meters, the safe zone is from 5 to 7 meters.

Mars' atmosphere is immense, at the higher Amazonian rate, it will still take 55000 years to fill Mars' atmosphere with oxygen to a breathable level. But, where would you get that much oxygen? What mechanism could generate nearly 300 tons of oxygen per second?

The real question is, where does all that oxygen come from? Without any way to explain that, I have to label this one, non-realistic.

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    $\begingroup$ @dreadzone11 You need a lot of oxygen over a very long time, no matter what the storage system. Whether this is realistic in the context of your world is up to you. $\endgroup$
    – kingledion
    Feb 16, 2018 at 15:37
  • $\begingroup$ Human living range is 0.1 to 1.5, not 0.1 to 0.5 bar of oxygen and 0.01 to 0.15 bar of carbon dioxide if we want to allow individuals to sleep (in absence of environmental carbon dioxide, you will have to remember constantly to breathe). $\endgroup$
    – Erkin Alp Güney
    Nov 6, 2018 at 7:13
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The only way you could make this work is if you went deep underground and had large cave structures with limited access to the outside world. This could allow a more realistic production of Oxygen to escape more slowly and thus have survivable pressure in the cave.

Of course you now have the problem of no daylight..

A better way might be to have pressure domes and suits, but have the inhabitants not know how they work. Suit maintenance and pre-use checks would be akin to religious rituals, as would repairs on the domes etc. They don't even see them as technology, they are just part of how the world works that they have always lived with and failing to properly sacrifice oil to the Suit God has a vivid and memorable punishment from the gods; when the joint fails and the inhabitant is exposed to near vacuum. Apostates are fine if they keep the core tenants (important safety checks and maintenance) and die if they don't.

A final option would be to have mars partially terraformed, enough to have a (perhaps low pressure but livable) atmosphere. There are a number of proposals for doing that including https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html

What they found was that a dipole field positioned at Mars L1 Lagrange Point would be able to counteract solar wind, such that Mars' atmosphere would achieve a new balance. At present, atmospheric loss on Mars is balanced to some degree by volcanic outpassing from Mars interior and crust. This contributes to a surface atmosphere that is about 6 mbar in air pressure (less than 1% that at sea level on Earth).

NASA proposes a magnetic shield to protect Mars’ atmosphere At one time, Mars had a magnetic field similar to Earth, which prevented its atmosphere from being stripped away. Credit: NASA As a result, Mars atmosphere would naturally thicken over time, which lead to many new possibilities for human exploration and colonization. According to Green and his colleagues, these would include an average increase of about 4 °C (~7 °F), which would be enough to melt the carbon dioxide ice in the northern polar ice cap. This would trigger a greenhouse effect, warming the atmosphere further and causing the water ice in the polar caps to melt.

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  • $\begingroup$ Thanks, you have just invented a way to invite reluctant Muslims to live on Mars. Now you need to find a way to raise your religious technicians. $\endgroup$
    – Erkin Alp Güney
    Nov 7, 2018 at 16:52
  • $\begingroup$ Not sure why you're picking Muslims as your go-to religious example. There are plenty of weirder examples out there than them. $\endgroup$
    – Tim B
    Nov 7, 2018 at 22:06
  • $\begingroup$ Because, Muslims are ones that use forceful spread. And, there are billions of them. $\endgroup$
    – Erkin Alp Güney
    Nov 8, 2018 at 9:03
  • $\begingroup$ @ErkinAlpGüney All branches of the Abrahamic religions do that, Christianity arguably being the most successful. At the end of the day all religions are parasitic memes and only parasites that manage to spread themselves survive so we shouldn't be surprised that all big religions are contagious in some form even if the exact way they propagate varies. $\endgroup$
    – Tim B
    Nov 8, 2018 at 9:49
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Yes, it is possible. Consider that at the bottom of a valley one is closer to the center of mass of the planet, thus gravity can be relatively stronger, and this could reflect on the local atmospheric pressure.

gravity vs distance from center

On Earth we don't have valleys deep enough to experience dramatic difference, but we have such feature on Mars: Valles Marineris.

Up to 7 km deep, the pressure at its bottom is about 0.168 psi, while the average atmospheric pressure on Mars is 0.087 psi. About double, as you see.

Still not high enough to take a walk in T-shirt, but if the atmosphere on Mars would be more dense, it would be first spot to achieve habitable conditions.

(this answer has been posted initially to this question, posting it here since it also answer this one. Credits @Willk for the hint)

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  • $\begingroup$ Maybe the ancients excavated the floor of this ancient rift, making it even deeper. The deeper it is, the more atmosphere is on top and the higher the pressure is. You could state that these excavations hit ancient pockets of gas, relics of the original Martian atmosphere trapped in the subsurface. The settlement in the bottom of the trench is nearly 1 dimensional - a narrow line hemmed in by the walls. It asks less to keep this deep, narrow area provisioned with atmosphere. Also it would be freaking claustrophobic! $\endgroup$
    – Willk
    Nov 7, 2018 at 20:07
  • $\begingroup$ I think this is a good answer – it works, there's nothing to break down, and you wouldn't even need to replace the air (eventually). According to my back-of-the-envelope calculation, if you dig a hole 80km deep on Mars, the air pressure at the bottom will be the same as in Denver, though In real life it would be unbreathable carbon dioxide. (en.wikipedia.org/wiki/Barometric_formula). But this doesn't have anything to do with varying gravity; it's just that the deeper you are, the more air is weighing down from above, and so the higher the pressure. $\endgroup$
    – bobtato
    Dec 5, 2018 at 13:18

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