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I'm making a world which is set on a planet with two smaller "bubbles" of atmosphere at the poles, and a more stereotypical atmosphere that surrounds them. Each of the three atmospheres has a different gaseous composition (one of the smaller ones is mostly Earth-like, with an abundance of oxygen, while the other is mostly Carbon/Carbon Dioxide based; the larger atmosphere is made of thicker, denser gases.) In every atmosphere exists an entirely different ecosystem and set of organisms.

Is this scientifically possible? If not, how close can a planet get to this type of atmosphere?

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    $\begingroup$ Well we do have a hole in the ozone layer to this isn't completely impossible. $\endgroup$ – candied_orange Jul 29 at 2:05
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    $\begingroup$ You'd need something separating the two atmospheres... like an extremely tall wall. $\endgroup$ – Arkenstein XII Jul 29 at 2:13
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    $\begingroup$ @candied_orange A hole in the ozone layer as the basis for different atmosphere, really? Sorry to say it doesn't stand scrutiny. That's only a minor difference in an atmospheric layer (although it is important for us mere humans). $\endgroup$ – a4android Jul 29 at 3:40
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    $\begingroup$ @ArkensteinXII Sure thing. Extremely, extremely tall walls. $\endgroup$ – a4android Jul 29 at 3:42
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    $\begingroup$ @candied_orange there is no hole in the ozone layer. The only thing there is are small regional variations in the concentration of ozone in the upper atmosphere. This is no different from any other gas that makes up the atmosphere. Do not think of our atmosphere as solid layers of different gasses superimposed on each other, with holes in some of those layers containing nothing at all. $\endgroup$ – jwenting Jul 29 at 3:57
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I think your best bet is speed, and lots of it.

If you look at pictures of Jupiter and Saturn (and, to a lesser extent, Uranus and Neptune), you would notice belts and zones across the surface. On Jupiter, these are especially prominent because the belts (the dark bands, which fall) and the zones (the light bands, which rise) are composed of different gasses.

An image of Jupiter; south is up and the moon is Io; note the prominent stripes. Image supplied by space.com.

To get those belts and zones, you'd need a planet with a very short day (Jupiter's is on the order of 10 hours). Bear in mind that this will give you very high winds; you will have to consider what this will do to your biosphere. This also gives you the "opportunity" to create massive storms (a la the Great Red Spot) on the boundaries that last for years, if not centuries, creating all kinds of story potential.

One potential effect of the high winds: In large equatorial oceans, the winds might be going fast enough to whip the sea into a froth, effectively erasing the boundary between sea and sky. This might be what creates the tropical zone, as opposed to the polar belts.

In order to keep up your planet's speed, you will need to limit tidal forces (so no or very small moons) and internal drag (so no or very small equatorial landmasses). A bigger planet might also help, lending rotational inertia to the system.

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    $\begingroup$ Thanks for the tick. You might also want to google "Hadley cells", I feel they might be relevant. $\endgroup$ – No Name Jul 29 at 5:42
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    $\begingroup$ So then what does "day" mean in the context of Jupiter? On Earth it's how long it takes for the solid world to rotate once, but for a gas giant without (as far as we know) any solid surface? Also, how do you have "very high winds" without a surface for the winds to be relative to? $\endgroup$ – Mason Wheeler Jul 29 at 19:33
  • $\begingroup$ Officially, at least according to my source, the "surface" of Jupiter is where the air pressure equals one atmosphere (i.e., the average pressure at sea level on earth). The wind speed was probably relative to that. As for day length, it appears they (meaning NASA) measure the "wobble" of the magnetic field, although even that isn't fool proof (Saturn is being difficult in this regard). $\endgroup$ – No Name Aug 12 at 2:52
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These gasses you seek will naturally mix, if given the chance. Their unforced steady-state behavior is always a homogeneous mixing. This means that you need something which forces them.

Smog trapped over the city of Almaty, Kazakhstan during a temperature inversion.
- Wikipedia

Quite the stark contrast between the air around Almaty, Kazakhstan and the mountains above is it not? This is caused by an inversion layer. A warm layer of air traps the air below. In the case we see above, that trapped layer below is then filled with smog from the city.

An inversion layer on its own cannot cause what you seek. Eventually there will be mixing, and you will achieve equilibrium. However, if we have things producing metastable compounds under the inversion layer and something which breaks them down before they fill the upper atmosphere, you end up with a situation like Almaty. The environment below is quite clearly different than the environment above.

How long an inversion layer remains inverted is a question of geography and climate. You may have to work hard to create a geography that keeps a very strong inversion layer over large areas that is reliable enough to have the effects you seek. However, they can indeed last a long time. A famous example was the Great Smog of 1952, which blanketed London in smog for 4 days. It created such a brutal smog of coal smoke that 6,000 people lost their lives in those 4 days.

This fickleness may also be a useful plot point. Perhaps you have inversion layers most of the time, but every couple of years it clears up due to random luck with the meteorological conditions. This could be a time of great exploration before the layer settles in again and the biome-specific gas producers start driving the air composition back to the biome's unique balance.

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If a planet or large moon once rotated much faster than it does now, and if it has had a rigid mantle and not been tectonically active since before it slowed down, then the equator could be 100 or 200 miles higher than the poles -- high enough to rise above effectively all the atmosphere.

I can't imagine a combination of astronomical forces that would slow a planet's rotation without melting the mantle, but then the universe is full of stuff I couldn't have imagined, so just handwave it. That's more or less what Larry Niven did with Jinx.

Of course this gives two atmospheres, not three, but if the only purpose of the band of dense gases was to present an uninhabitable barrier, perhaps your story may work as well with vacuum separating the habitable worlds.

If you use this construction, make the world as small as you plausibly can. A planet the size of Earth or even Mars could not have mountains 200 miles high even with a rigid mantle. Rock is just not that strong.

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  • $\begingroup$ Most celestial bodies have solid mantles (if they have one at all). I can think of very few exceptions. $\endgroup$ – Arkenstein XII Jul 29 at 3:48
  • $\begingroup$ @Arkenstein four stix: The Earth's mantle is believed to be fluid and in motion, and is the driving force behind continental drift. $\endgroup$ – A. I. Breveleri Jul 29 at 3:55
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    $\begingroup$ The Earth's mantle is, however, a crystalline solid. It is ductile over extreme time periods only. $\endgroup$ – Arkenstein XII Jul 29 at 3:58
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    $\begingroup$ As you wish but I am not going back to edit my answer to say "not a crystalline solid ductile over extreme time periods only" everywhere I have written "solid". $\endgroup$ – A. I. Breveleri Jul 29 at 4:02
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    $\begingroup$ Just say "rigid", which is the proper term anyway. Pillows are solid, but you would hardly use them as foundations for mountains, would you? $\endgroup$ – Luaan Jul 29 at 10:49
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Similar to the plant Jinx in Larry Niven's "Known Space" books, a planet with a "fossil tidal bulge" could have "ends" -- inner and outer (or East and West, as in the books) poles -- that stick up out of the atmosphere -- this could produce a high density/pressure atmosphere near the horizon zone (twilight zone for an "eyeball" planet of a red dwarf, or where the primary is on the horizon for a moon of a hypermassive gas giant as with Jinx) -- while the "ends" have an Earthlike atmosphere, or even no atmosphere surrounded by a "ring" of habitable pressure and composition.

Formation of such a bulge would require the planet's/moon's orbit to have moved away from its primary over time, after the mantle and core have cooled enough to limit the amount of adjustment for the reduced tidal stretching. My limited understanding is that this is unlikely, give what we now know about tidal heating (the engine that keeps Europa's ocean liquid, among other examples), but I'd hesitate to call it impossible -- and the unlikeliest things happen if you look long enough.

Comments noted that the atmosphere will remain mixed, so the twilight band can't be a toxic composition -- but it doesn't need to be. Plain air will kill you fairly quickly (from oxygen toxicity) at not much over 7 atmospheres (and nitrogen narcosis might make you make a fatally bad decision at 2/3 that figure). Sure, there could be local critters that adapt to that -- but the very air would be deadly to wandering humans from the 1 atm. zone.

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  • $\begingroup$ This is the first thing I thought of -- Jinx -- but with the poles higher than the equator, a band of dense gases at the equator, and habitable atmosphere at the poles, that habitable atmosphere must cover the entire planet, lying over the equatorial bands as well as the poles. It will be thoroughly mixed. OP has asked for each pole to have a different atmospheric composition. Therefore I suggested exoatmospheric crust at the equator instead of at the poles -- sort of the opposite of Jinx. $\endgroup$ – A. I. Breveleri Jul 29 at 16:07
  • $\begingroup$ At what pressure does Earth's unaltered atmosphere become toxic? Nitrogen narcosis sets in around 70-100 psi. Oxygen is an active poison (in 20% concentration) at not much higher pressure. Not sure how much deeper that is than what we have, but if the ends stick out of the atmosphere, seems like the band must have this much pressure (5-7 atmospheres). No composition change needed, just pressure. $\endgroup$ – Zeiss Ikon Jul 29 at 17:01
  • $\begingroup$ There's also Niven's planet Plateau, which has a very dense atmosphere except on a plateau (Mount Lookitthat) that rises high enough to have an Earthlike pressure: en.wikipedia.org/wiki/A_Gift_from_Earth Of course a plateau couldn't be quite as high as that, due to geology. $\endgroup$ – jamesqf Jul 29 at 18:11
  • $\begingroup$ Yep, aka Mount Lookitthat. Actually, he wrote that story after reading that it was just barely geologically possible for a mountain to stand 40 miles high. Whether that's still believed to be possible (fifty-some years later) I don't know, but it was when A Gift From Earth was written. $\endgroup$ – Zeiss Ikon Jul 29 at 18:26
  • $\begingroup$ And much later, he wrote about Canyon (where Louis Wu had wound up before going back to the Ringworld). Atmosphere like Mars, except at the bottom of a canyon many miles deep cut with a Slaver disintegrator. $\endgroup$ – Zeiss Ikon Jul 29 at 18:28
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Since you asked specifically about poles: Saturn's Hexagon.

Though I'm not entirely sure if this meets your meaning of "bubbles" (to me, "bubble" implies having the larger atmosphere between the bubble atmosphere and space).

I'm also not sure if the edges of the hexagon would prevent gases crossing the boundary, but they may complicate/slow the crossing enough that the local life could keep up with maintaining their local atmosphere.

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