My world is that of a humongous cliff and pretty much nothing else. I was unable to be a flatlander so I justified it by making a humongous alien artifact and jabbing it into a polar region of a gas giant with a density of Saturn.

enter image description here Supposed view from the surface, to my limited painting abilities

(Yeah, I suppose the star wouldn't be able to be so high above the cloudline... Perhaps it's an orbital mirror.)

It is positioned above the ambient density of the gas giant, and it is dotted with "emitters", that spew out air and moisture, keping the air pressure leveled out and breathable for a wider band of the structure than it would otherwise been (I needed hundreds of kilometers wide band of habitability, but naturally it would be more like just a few kms before the atmosphere becomes too thin to breathe.) I was thinking about how the atmosphere might work on the structure like this, and came to this setup:

enter image description here

There are several bands of air zones:

Zone A is where the temperature and the pressure of the air drops too low for life to exist.

Zone B is where the oxygen levels and the pressure optimal to be roughly earth-like.

Zone C is where all the air and stuff from above begins to be compressed by the gas giant's own atmosphere, it is unpleasant, hot, and dark down there.

Band 1 is close to the surface that breaks down the air flow, and it is a quite turbulent zone with relatively unpredictable winds.

Band 2 is the transitional zone, where the air currents are relatively uniform and calm, flowing outwards, pushed away by the air generated by the emitters.

finally, there's band 3, where the air generated by the structure begins to mix with the unbreathable atmosphere of the gas giant, and due to it being more dense than it, falling down into the abyss, forming a rather strong downdraft that drags everything caught there down with it and forming a wall of clouds on the outer side in a sort of reverse eye of the storm fashion.

So if you go too high, you'll freeze, if you descent too deep you'll be crushed, and if you'll stray too far from the surface you'll be caught up in a downdraft and dragged below, where you'll be crushed. This should nicely box the inhabitants of the slope close to the surface, by limiting where the airships can relatively safely travel (The green area), preventing them from straying too far from the surface and realize that it is not in fact a flat wall (Up close enough it's uneven structure should be hiding the curvature rather nicely).

I imagine that bands 1 and 2 would be rather thin, extending outwards from the surface of the structure to no more than a few kilometers.

So, does this makes sense? The game I'm doing this for isn't intended to be hard science fiction (it's a steampunk platformer (Justified by the setting to be a platformer!) with "magic"), so if it isn't entirely lines up with equations, that should be fine by me.

  • $\begingroup$ How high is the mountain? (And how big is the planets core) Just if it's over a certain mass gravity will turn it into a ball at the centre of the planet. If the centre of mass of ( the iron core and the mountain ) isnt at the core centre, the mountain will sink until the centre of gravity is the centre of the planet. $\endgroup$
    – Ash
    Oct 27, 2020 at 11:49
  • $\begingroup$ It's a spindle-shaped alien superstructure that's 3000 km wide at the tips and 120k km long, going right through the gas giant and supposedly completely replacing its rocky core. I don't think it's structural integrity is a thing to worry about. =) $\endgroup$ Oct 27, 2020 at 11:57
  • $\begingroup$ I do. Your mountain will collapse into the core of the planet, compressing the rock into new molten lava and spreading out into a sphere under the clouds. Maximum height of a gentle sloping mountain is 1413km or 22km if it's sharp cliff. If it isn't crushed, what's keeping it buoyant and not interacting with the centre of gravity of the planet? $\endgroup$
    – Ash
    Oct 27, 2020 at 13:19
  • 1
    $\begingroup$ if it's not hard science, then yes, perfectly plausible, no need even for the long winded explanations... $\endgroup$
    – Kilisi
    Oct 27, 2020 at 14:41
  • $\begingroup$ That is not a mountain, its an alien superstructure. A technological artifact. And it is at the center of the gravity of the planet. What exactly is your logic in treating it as a natural rock formation? i.gyazo.com/52200143cfd479c41581fbfa06e29353.png $\endgroup$ Oct 27, 2020 at 14:43

2 Answers 2


Yes, with a bit of hand waving

Based on your comments stating that it pulls gas out from the planet, this eliminates the whole "needs a lot of air to do that" part. Considering oxygen and nitrogen and other gases they will want to move down. The hand wavy part begins with when you realize the other gas (and therefore clouds) will want to move upwards, which means you need some weird windy stuff pushing down from above as well and your outer cloud layer might not be as smooth as pictured in the drawings. Other than all that this setup seems pretty good and really interesting for a story.


Not without a counter-balancing air consumer or force field. Your entire idea is premised on being able to displace the atmosphere of the gas giant by essentially blowing a lot of air around the mountain. The issue is that is a LOT of air. A lot. You are displacing a huge amount of the planet's atmosphere all the time, and it will want to keep mixing with your atmosphere. Therefore, the ambient gas giant atmospheric pressure has to be lower than the pressure at your breathable zone, and the breathable air has to be constantly pushing the gas giant's air away.

In order for this to be possible, either you need to consume the air at the edges, presumably filter out the bad stuff that happened at the interface (the mixing) and recycle it, or something, and refresh it, OR you need a force field to keep the bad atmosphere out. With a force field then the mixing zone never happens, so it looks like you're going to need to consume it.

  • $\begingroup$ What do you mean, "consume" it? The rough idea is that the structure essentially converts the gas giant into oxygen, nitrogen, and water - sucking it in somewhere deep or maybe even at the opposite pole. I assumed that constantly spewing out clean air would be enough since it would be displacing the mixing air outwards? To the boot, yeah, the gas giant's atmosphere pressure is lower at those attitudes, since we're artificially extending the 1 atm area near the surface upwards via the air emitters. $\endgroup$ Oct 27, 2020 at 18:51
  • $\begingroup$ Yes, that should do, in a hand-wavy sort of way. As long as you aren't magicking mass into existence and pumping it into the atmosphere you should be good to go $\endgroup$ Oct 27, 2020 at 19:04
  • $\begingroup$ You will, however, have CRAZY winds at the mixing boundary $\endgroup$ Oct 27, 2020 at 19:04
  • $\begingroup$ That's a good thing. =) Especially if those winds would be downwards as I estimated. $\endgroup$ Oct 27, 2020 at 20:27

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