I've read all the related questions on here and as far as I can tell this should be breathable on my planet Liskuel, which has 1.5 bars of pressure. However, I'm really bad at maths and don't really know how to scale it up with atmospheric pressure, so I would really appreciate a fact check.

Edit: I've updated the stats to match some feedback I got, but just so the original answers make sense, here are the original stats: enter image description here

...And here are the updated stats (more oxygen and water vapour): enter image description here

Additional query: I've included a fair amount of Xenon - do you think there is enough to accumulate in the lowest valleys and knock out your average human?

  • $\begingroup$ Breathable for how long? $\endgroup$ – Ash Aug 7 '19 at 12:27
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    $\begingroup$ Your water-vapor content is way to high. Earths standard one is 0.0025 atm. Sure, it does varry between 0 and 0.04 atm, but thise are extremes. You'll usually find out the maximum possible water content via calculating the water vapor saturation pressure. Calculate your planets global average temperature and multiply it with 0.25. Thats the average water content of your atmosphere. $\endgroup$ – TheDyingOfLight Aug 7 '19 at 12:46
  • $\begingroup$ @Ash incessantly. $\endgroup$ – MissMermaid Aug 7 '19 at 22:59
  • $\begingroup$ @TheDyingOfLight That's wonderful information, thank you! Do you have any tips for calculating the global average temperature? I will of course do my own research, so feel free to ignore. $\endgroup$ – MissMermaid Aug 7 '19 at 23:04
  • $\begingroup$ Firstly I messed up with the aproximation formula. Multiply with 0.125, not 0.25. Planetary equilibrium temperature is a good starting point to get a planets temperature. I prefer the stellar temperature based equation. This video is very useful for determining the albedo of your world. $\endgroup$ – TheDyingOfLight Aug 8 '19 at 8:43

What matters for breathability is the partial pressure of the gas.

According to Dalton law

$Partial\ Pressure = Total \ Pressure \cdot volume \ fraction$

For Earth

$P_{O_2}=1 [bar]\cdot 0.21=0.21 \ bar$

On your planet

$P_{O_2}=1.5 [bar] \cdot 0.055=0.08 \ bar$

That's a tad more than the partial pressure in the Death Zone on Mount Everest

at the top of Mount Everest the average person takes in about 30% of the oxygen in the air that they would take in at sea level; a normal human person used to breathing air at sea level could only be there for a few minutes before they became unconscious.

Therefore the atmosphere of your planet is at the limit of breathability, and would require proper acclimation to not be lethal.

That apart, it is also pretty dry, which is an additional issue, though not impacting breathability.

After your edit:

$P_{O_2}=1.5 [bar] \cdot 0.105=0.16 \ bar$

which is breathable, comparable to what we breathe when we are on a mountain.

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    $\begingroup$ @MissMermaid, FYI this is not a forum: on a forum you post a question, get answer, change the question and so on in a potentially endless loop. Here one posts a question, gets an answer and that's it. $\endgroup$ – L.Dutch - Reinstate Monica Aug 7 '19 at 6:28
  • $\begingroup$ Ah, gotcha. Sorry! $\endgroup$ – MissMermaid Aug 7 '19 at 6:31

Probably breathable but almost certainly dangerous:

  • The recommended 8 hour Ozone exposure is at most 0.1ppm, that's a thousandth of your atmospheric concentration. Given that studies have shown that tiny increases of just 0.001ppm cause notable increases in fatalities this is almost certainly a sizeable problem in a continuous exposure scenario.

  • The other thing that makes this situation dangerous is the fact that breathing that much Nitrogen under that much pressure is the equivalent (1.245bar post edit) of being in a constant SCUBA dive at a depth of roughly 6 metres, while many people will notice little to no effect from this, at least initially, many others will be immediately, if lightly, impaired (approximately the equivalent of drinking two thirds of a martini an hour). As the long term build up, over days or weeks instead of hours, of dissolved Nitrogen in the blood is not a well understood phenomena the effects of this may lessen or worsen over time.

To address the Xenon issue, no probably not, Xenon anesthesia is only effective in a 70/30 mix of Xenon to pure Oxygen there's simply not enough of it to concentrate to that degree. Having said that in combination with the mild narcotic effects of the Nitrogen and its oxides lower concentrations may prove to have some effect.


As for the breathability of the atmosphere. I encountered this list in a video by worldbuilding YouTuber Artifexian and have added to it since. I did check several values and found them to be correct. Going down the list it became increasingly difficult to verify the values, so take everything without a link with a grain of salt.

1.25 atm, o.k

0.015, o.k

not found

0.00045 atm, o.k

  • SO2 < 0.000005 atm

not found

0.000165 atm, exceeded by 3 orders of magnitude

0.1725 atm, low but o.k

  • Ar < 1.6 atm

0.00006 atm, o.k but very low, see below

not found

  • Xe < 0.21 atm

0.00135 atm, o.k I would be surprised if anyone would even notice, nevermind get knocked out.

There is surprising little Argon in the atmosphere.

Nearly all of the argon in the Earth's atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the Earth's crust. In the universe, argon-36 is by far the most common argon isotope, as it is the most easily produced by stellar nucleosynthesis in supernovas. - Wikipedia

Argon isn't in the atmosphere by chance but as a result of the alpha decay of potassium-40. This means that the planet is either very young (not older than maybe 0.5 byr at most), in a low metallicity system (meaning it would most likely be a planet dominated by water), lost its original atmosphere in a geographically speaking recent event, is an artificial world around a gas giant or black hole or is so small (moon-sized) that it had little radioactive material, to begin with. If none of these assumptions are correct, I suggest adding argon.

And you are going to have one hell of a greenhouse effect CO2(factor of 4.5), H2O (factor of 24), CH4 (factor of 3), NO3 (factor of 4.5), O3 (factor of 41.25) and H2 (no direct effect, yet it increases the lifetime of other gases) are relevant for the greenhouse effect. Ignoring anything but H2O and CO2, which are responsible for most of Earths greenhouse effect (this is not really a clean approach as you added even more of the minor and stronger greenhouses gases) we see that you increased those by a combined factor of 66. Now calculating greenhouse effects is really hard and requires simulation programs, but it is save to say that it will be way higher than Earths 33 K. Maybe 150 K? Now you are either dealing with a planet with a runaway greenhouse effect, which is on the way to become an exo-Venus or one still habitable but near the outer edge of the habitable zone. In Solar system terms, this means out beyond Mars or even in the asteroid belt.

Where does this leave us? Ozone is way too common but it might still be fine because ozone is usually found in the ozone layer and not in the troposphere. The greenhouse effect might turn the planet into a cooking-pot. Then the air won't be breathable because it will boil you alive. Avoid getting the planet hotter than 47 °C to avoid the greenhouse effect. So apart from this, the fact that there is an odd lack of argon and that your greenhouse effect will be enormous compared to Earth the atmosphere is breathable.

  • $\begingroup$ Very informative answer. But the OP is asking if the atmosphere is breathable, and that point is not touched at all here. Moreover, being a hard science question, citations are expected. $\endgroup$ – L.Dutch - Reinstate Monica Aug 7 '19 at 9:40
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    $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – Ash Aug 7 '19 at 10:18
  • $\begingroup$ @Ash Currently editing to meet requirements, do not delete. $\endgroup$ – TheDyingOfLight Aug 7 '19 at 10:32
  • $\begingroup$ @Ash Edit it to fit question. $\endgroup$ – TheDyingOfLight Aug 7 '19 at 11:47
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    $\begingroup$ You are answering "is the planet livable?", which is not the OP's question. $\endgroup$ – L.Dutch - Reinstate Monica Aug 7 '19 at 11:52

I have not done the maths, but using common sense and some research I have got you an answer. At 5% oxygen concentration on earth, with one bar of pressure, you start to die, although with 1.5 bars of pressure you would definitely survive. It seems (at least with my understanding) that with a 5.5% percent concentration of oxygen would act like 8.5% concentration of oxygen. This concentration is normally not enough for a human to survive, although it is likely that we would be able to adapt by increasing the amount of hemoglobin in their blood. There also doesn't seem to be enough water, which could lead to a lot of deserts. hopefully, my math is correct and I have helped you with this. edit: I actually did the math, and didn't plan to at the start so I wrote it wrong. sorry. https://www.thenakedscientists.com/forum/index.php?topic=44734.0 source for the amount of oxygen needed

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    $\begingroup$ The question is tagged hard science. doing the math would help. $\endgroup$ – L.Dutch - Reinstate Monica Aug 7 '19 at 5:24
  • $\begingroup$ I did do the math, I just forgot to fix it. $\endgroup$ – meaninglessname Aug 7 '19 at 10:44

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