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I'm developing a desert world with polar ice caps, but the majority of the planet is covered in scorching desert terrain. The ice caps, though present, are relatively small, and the areas near the northern and southern polar circles consist mostly of very cold steppes or cold deserts.

Water sources are concentrated in the remnants of previous seabeds that have either dried up or are in the process of drying out. These seabeds are located off the continental slopes.

To illustrate the planet's topography:

Mountain ranges span from sea level to 6000 meters in height.
The desert and hot climates occupy areas from sea level to 0 meters.
The former seabeds lie at depths ranging from -2000 to -3000 meters.

My concept revolves around the idea that the entire planet is habitable, but regions with former seas are cooler due to the lingering influence of water. Therefore, these sea bottoms are the most favorable areas for human habitation and cultural development. Additionally, I envision strong convectional winds facilitating the use of kite systems and piloted balloons for navigation throughout the atmosphere.

My question is whether this setup is physically plausible. I'm not seeking intricate calculations regarding flight capabilities; rather, I'm interested in knowing if the overall system makes sense. To summarize, the deserts are hot but livable, with nomadic caravans and tribes. The former seabeds provide the most hospitable environments for cultures to flourish. The northern regions are cold but not excessively icy, while the mountain ranges may or may not feature snow-capped peaks. Ultimately, the planet is predominantly characterized by vast expanses of sand.

Does this scenario hold up to scrutiny, or are there any glaring inconsistencies? Any insights would be greatly appreciated.

Edit from Answers:

From the answers received I understand that it can be plausible but I need to restrain some features like: Ice caps present fuel and dilute the salinity of the sea Some underground water stream contribute as well and come from under the deserts levels. Pressure could be too hard at -3000 m under desert level but at 1000 m could be better making liveable both -1000 and up to +4000m with deserts in the middle still liveable. The more density of the air in the depression can help the buoyancy of my planned flying kites. the bottom of the chasm can be cooler due to presence of sea mitigating effect and stabilizing a bit the temperature excursions in upper deserts the temperatures can vary from very hot to very cold convective currects form due to the nature of the place and peculiar features.

Is all that fine and working? Or there are some other hindrances to take care of?

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    $\begingroup$ Bear in mind (if you're trying to be reasonably realistic) that your mostly-evaporated seas would be very, very salty. Great Salt Lake levels of salty, or Dead Sea. There might be fresh water nearby, from a localized evaporation / condensation cycle, but the seas would be salt saturated and possibly surrounded with salt flats. $\endgroup$
    – Jedediah
    Commented Feb 7 at 15:24
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    $\begingroup$ If you are not already familiar, a google search on "Messinian salinity crisis" may provide some perspective. $\endgroup$
    – Gillgamesh
    Commented Feb 7 at 15:25
  • $\begingroup$ Though in my envisioned concepts thare is a constant flow of rivers all around and especially from the connection to the northern icecaps, if you check my post to the following answer you can see a link to the map . Ideally the other rivers could come from underground sources but from high tops inside the cliffs. $\endgroup$
    – Naima
    Commented Feb 7 at 16:32
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    $\begingroup$ Where did all the water from these enormous seabeds go? Mars lost its water when it lost most of its atmosphere, but that doesn't seem to be the case here. $\endgroup$
    – jdunlop
    Commented Feb 7 at 19:11
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    $\begingroup$ "Under soil" doesn't explain cubic kilometres of water vanishing. Dune, at least, had a biological explanation, and Tatooine never had much water to begin with. You postulate a planet with seabeds and the oceans are gone. $\endgroup$
    – jdunlop
    Commented Feb 8 at 18:44

2 Answers 2

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Is "sea-level" (0 meters) in your world experiencing 1 atm? if so, humans trying to live at the bottom of the ocean chasms would have a very bad time.

Conversely, if 1 atm is the pressure at the actual water level on the seabed, at -3000 meters, then life above the 0 meter level is extremely unlikely and any place significantly above 0 meter level is basically in vacuum.

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  • $\begingroup$ Is this so Drastic? In case I coul dreduce the height of the chasm cliffs? I want the desert be liveable if needed, just a harsh environment, the bottom can be better because of large jungles etc? May be reduce to 1000 m or 2000 m? $\endgroup$
    – Naima
    Commented Feb 7 at 15:48
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    $\begingroup$ AFAIK, there should be 3-4 bars at 1000km down the hole, which would be very very bad for you. Not instantly deadly, just really unhealthy, and extremely uncomfortable. For reference, diving about 10 meters underwater puts you in 2 bars of pressure. It is survivable, easily, but uncomfortable. Not sure if you ever trying freediving that deep, but consider how weird your ears feel at the bottom of a regular swimming pool, where the pressure is only a little bit over normal 1.1 bar you evolved to live at. Now make it over 25 times worse. Thats what you get at 1000m into the chasm. $\endgroup$
    – Going Durden
    Commented Feb 8 at 9:16
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    $\begingroup$ @Naima. IRL, there are miners who work in shifts at 3000meters or even as far as 4000meters. It is survivable, but absolutely sucks. At anything above 2.5 bar, you get nasty side effects from the oxygen reacting weirdly with your body. At 5 bar-ish, the air thickness, moisture and heat conductivity means you simply inhaling nasty lukewarm soup at all times, suffering long exposure barotrauma and constant low-key hallucinations due to nitrogen poisoning. My guess is, if your people are really tough badasses, they can live as far deep as 1000-1500m, and going below that only for short trips. $\endgroup$
    – Going Durden
    Commented Feb 8 at 9:30
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    $\begingroup$ @Naima, How long and at what tech level? If you mean that all the people lived there since birth they would simply adjust to thick air and high oxygen density by volume. They would suffer from earache, clogged sinuses and cardio issues more often though. They would get heat strokes or hypothermia more often. Possibly more miscarriages. They would speak more softly, and breathe more shallowly. Slower heartbeats. More stamina, strength and speed at the cost of health and more caloric needs. Age faster, and more cancer due to oxygenation. Plenty of burn scars from hyperoxygenated flames. $\endgroup$
    – Going Durden
    Commented Feb 8 at 10:37
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    $\begingroup$ @Naima: it needs as much of an adaptation as people living 1000m over the sea level, just different. Completely doable, especially for people who were born there and shaped by it from conception. No need for them to even evolve towards that, just in vivo adaptation. The biggest differences are oxygen and heat. at minus 1km, things oxygenate and heat a little quicker than normal, which would get some getting used to. For example, it makes breathing more efficient, and thus muscles more efficient, but at the risk of hyperventilation. $\endgroup$
    – Going Durden
    Commented Feb 8 at 11:12
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On a desert planet, the little water that is available usually evaporates and settles where it's cold overnight, a la Mars. So there can always be water below frozen dunes in lightless canyons and even icy marshes - cold stays down, not affected by the day's heat much. It's different with open water - it constantly evaporates, thus shrinking without rain or underground rivers.

Which makes it salty - the water in the rifts would be much like the Dead Sea or Aral Sea were/are.

There could be condensing moisture on the slopes nearby, at night when everything cools down. That moisture could keep plants alive (more the deeper you get) and even create morning fog/clouds. The ecosystem could be hyper-adapted to keeping that moisture in (basically like sponges) with enormous shade throwing leaves.

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  • $\begingroup$ The sea I envision though is as large as double the size of mediterranean. $\endgroup$
    – Naima
    Commented Feb 7 at 12:55
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    $\begingroup$ How huge are the glaciers at the poles and how long has the transfer of moisture from the sea to the glaciers of geologic time been going on? As in how big did it start out? $\endgroup$
    – Pica
    Commented Feb 7 at 13:24
  • $\begingroup$ You can see a picture of the world here ... deviantart.com/n-a-i-m-a/art/The-Last-Sea-Of-Ausur-942695235 But consider that I am changing the size to be an Earthlike and this will only be the upper one side hemisphere . $\endgroup$
    – Naima
    Commented Feb 7 at 13:35
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    $\begingroup$ What is the unnamed one in the jungle of umbar? $\endgroup$
    – Pica
    Commented Feb 7 at 14:27
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    $\begingroup$ Thanks go to @jdunlop for fixing the typos. Shame on me! $\endgroup$
    – Pica
    Commented Feb 8 at 8:24

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