This post: How to increase air density on a planet? explains most of the problems I have been having, and fixes them. My current problem is as follows: On a planet with an air composed of (roughly)

21% Oxygen 39% Nitrogen 39% Krypton + the required C02

The density will be higher to allow hydrogen and helium to be more effective as lifting gases (my goal). I am assuming wind is enough to mix the krypton and oxygen in most places, if this isn't the case, please do point it out. Additionally; humans will need to have evolved filters to prevent the annoying side effects of breathing krypton (death through suffocation as a result of oxygen displacement, and an excessively low voice). I understand that lower parts of land, or places with not enough wind to mix oxygen and krypton will be uninhabitable. Also understand that as the aircraft ascend, the air will more and more be composed of oxygen and less krypton, leading to lower density and less effective lifting power.

My questions: would the increase in proportional oxygen as heights increase prevent the effects of hypoxia because the partial pressure would remain more similar?

I am flexible on the specific amounts, and open to the inclusion of xenon or argon also. The density of the above atmosphere (according to my inexpert calculations) would lead to helium being almost twice as effective. This is the goal, if it can be pushed higher I would like that also, though I know nitrogen is important for plants.

Would this composition require a different atmospheric pressure?

I also want to know if there are any other problems to deal with.

  • $\begingroup$ Welcome to WorldBuilding Groblin! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Jul 7, 2017 at 6:53
  • $\begingroup$ In a krypton atmosphere there would be no lowering of the voice. Also be aware that you already are being unscientific with your atmosphere, krypton is not common enough to make up a natural breathable atmosphere. Maybe since all physics is already out the window... $\endgroup$
    – Raditz_35
    Jul 7, 2017 at 7:28
  • $\begingroup$ @Raditz_35 why not lowering the voice? $\endgroup$
    – JDługosz
    Jul 7, 2017 at 10:03
  • $\begingroup$ Why mess with atmospheric composition and not just increase the pressure (see Mike Nichols' comment to the original question). $\endgroup$
    – Alexander
    Jul 7, 2017 at 17:00
  • $\begingroup$ Thank you for the responses. 1: as far as I know, sound moves slower through krypton, leading to lower voice. 2: The rarity is not a problem, this world has been designed by a higher power (without going into too much boring detail it is pretty much designed to make lifting gas better) 3: I will research the pressure's impact further, thank you for the clarification. $\endgroup$
    – Groblin
    Jul 8, 2017 at 1:48

2 Answers 2


Another potentially-annoying side effect of having lots of krypton in the atmosphere is a mild sedative effect. That's only really significant at hyberbaric pressures, though, so if the total atmospheric pressure remains similar to Earth's, you can probably ignore it. A useful side-effect, however, is that krypton may stimulate red blood cell production, which means humans will be able to handle lower oxygen concentrations than they otherwise would. That may prevent the onset of symptoms of hypoxia at higher altitudes (for people who have been the planet for a while, anyway; it wouldn't work for brand-new arrivals), but within the altitudes where aerostatic flight is reasonable, there will be no significant gradations in atmospheric composition with altitude.

Evolving filters to avoid the effects of krypton is also pretty useless. If you are in a place where krypton has displaced too much oxygen, filtering out the krypton by itself will not help you survive- you'll just be left with not enough oxygen, rather than not enough oxygen plus some krypton. And if you want to eliminate the effects on one's voice, the filter would need to be placed outside or near the front of the mouth, and covering the nose. If the voice change is really bothersome, I could see developing a mask for that purpose, but there's no good biological solution that does not involve major changes to basic human vocal anatomy.

  • $\begingroup$ Thank you for your response! I believe that inhaling almost 40% krypton would lead to inert gas asphyxiation, in which krypton takes up all the space in the lungs. Given I agree on your filter observations, I believe I must seek alternative solutions. Like an increase in atmospheric pressure. $\endgroup$
    – Groblin
    Jul 10, 2017 at 2:55
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    $\begingroup$ @Groblin Inhaling 40% inert gas along with 0.2+ atmospheres of oxygen won't cause asphyxiation; inhaling inert gas instead of oxygen will. 70+% of our own atmosphere is inert gas, but you don't get inert gas asphyxiation from inhaling all that nitrogen along with the oxygen. $\endgroup$ Jul 10, 2017 at 3:34
  • $\begingroup$ Sorry, I did not articulate my point accurately. Krypton gas is far more heavy than oxygen (the whole point of replacing nitrogen with it in the air) and can therefore sit in the lungs without being expelled, meaning the oxygen needed cannot get in. $\endgroup$
    – Groblin
    Jul 10, 2017 at 12:24
  • $\begingroup$ @Groblin - Then people will need to stand on their heads, in order to eliminate the heavier gas... $\endgroup$ Jul 10, 2017 at 13:28
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    $\begingroup$ Even if it were possible to efficiently separate the gasses while they are in the lungs, collecting krypton at the bottom (which it is not), pools of krypton in the lungs would still be pumped out during exhalation. Were it not so, you wouldn't see people inhaling sulfur hexaflouride as a stunt on TV. $\endgroup$ Jul 11, 2017 at 14:07

I believe you are making an incorrect assumption about the relative % composition of the atmosphere changing significantly as you ascend.

Using Earth's atmosphere as a model the atmosphere is divided into fairly distinct physical layers.The bottom layer (Troposphere) is where practically all the weather happens and where the majority of the matter in the atmosphere is. This causes it to be very uniformly mixed as regards light "objects" such as molecules.

It does experience a significant change in both pressure and temperature with increasing altitude. It is these changes that are the primary danger to balloonists. Hypoxia due to altitude is caused by the overall lack of air not by a change in the % of oxygen in the air.

The layers above the Troposphere are not mixed by weather and are thus very stratified and stable in composition. They are also far too sparse to support even the lightest balloons.

Replacing some or all of the Nitrogen with a gas with higher molecular mass will, due to gravity, increase the pressure at sea-level and therefore actually decrease the overall height of the Troposphere. So your balloons wont be able to fly as high (but they will be able to get there quicker!).

It might be useful to state the actual objectives of the powerful agents doing this mega-scale engineering project (in a new question). There may be completely different solutions. (i.e. they maybe able to build an ultra strong and lightweight balloon that can simply hold a vacuum without collapsing ? Perhaps they could arrange a smaller/lower gravity planet with lots of extra atmosphere that is held in place from leakage into space?)

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    $\begingroup$ I am not competent enough about atmosphere composition, but Your statement about "They are also far too sparse to support even the lightest balloons" is surely wrong (see: en.wikipedia.org/wiki/High-altitude_balloon) $\endgroup$
    – ZioByte
    Jul 9, 2017 at 21:19
  • $\begingroup$ Thank you for your response! I believe that Hypoxia is caused by an excessively low partial pressure of oxygen, which is caused by a lower amount of total air. However, nitrogen is useless to human lungs, so if there was a higher % of oxygen, the partial pressure of oxygen would be more, leading to lower chance of hypoxia. The idea is to have a world with more effective helium, leading to more prolific usage of Airships by all parties. $\endgroup$
    – Groblin
    Jul 10, 2017 at 5:03
  • $\begingroup$ @ZioByte from that page "..that are released into the stratosphere..". I was referring to the layers above the stratosphere. $\endgroup$ Jul 12, 2017 at 20:50
  • $\begingroup$ @JohnMcNamara: sorry, I didn't read You right (it seems). The phrase started: "The layers above the Troposphere" and I assumed the rest also applied to anything about troposphere. $\endgroup$
    – ZioByte
    Jul 12, 2017 at 20:56
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    $\begingroup$ @JohnMcNamara: I do completely agree. see: en.wikipedia.org/wiki/Red_Bull_Stratos ;) $\endgroup$
    – ZioByte
    Jul 12, 2017 at 21:11

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