Could a singular planet have more than one diverse atmosphere?

Question

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?

Answer 1

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.

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.

Answer 2

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.

- 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.

Answer 3

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.

Answer 4

I can't imagine a combination of astronomical forces that would change a planet's shape 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.

Now if, instead of forming in a higher gravity gradient, 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.

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 still feel you need a third atmosphere, for reasons other than just separating the two bubbles, you can declare that it wraps the whole planet, above the two bubbles and above the mountains.

A little more handwavium serves to keep the upper atmosphere from mixing with the bubbles, and any cross contamination can be absorbed by the biohemispheres.

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.

Answer 5

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.