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Is it possible for a dry planet similar to Earth* to be inhabited by an indigenous intelligent humanoid species that is restricted to a small area of the planet – perhaps 1000 miles x 1000 miles near a small sea with a benign “local” climate and be entirely isolated from other areas of the planet by deserts?

Assume that plate tectonics still continues as per this question**. Assume the species has a pre industrial state of technology.

*The planet has a strong magnetic field, rotates on its axis every 24 hours, has a hot core and is volcanically active. The planet orbits a Sun like our Sun at roughly the same distance and the planet also has a large Moon similar to our Moon. But it has much less surface water in seas, rivers and icecaps (2-10% of Earths).

**How much surface water do I need for plate-tectonics on a planet?

Related questions Could a planet with no satellites and no tectonic plates be habitable?

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  • $\begingroup$ it has much less surface water in seas, rivers and icecaps (2-10% of Earths) I am dubious that this lack of water would allow much life to develop in the first place - not life as we know it. $\endgroup$
    – StephenG - Help Ukraine
    Commented Oct 21, 2020 at 13:11
  • $\begingroup$ @StephenG why do you think so? The seas are still a significant size in some areas - many hundreds of miles across. How large an expanse of water is needed for life to arise? $\endgroup$
    – Slarty
    Commented Oct 21, 2020 at 13:46
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    $\begingroup$ This raises just many questions - how does the sea survive ? The Earth is covered by area to about 70% water. You want at most 10% of that, so you are talking about an area of about 7% Earth's area at most, so at most about a 6000km by 6000 km by 6000 km ocean. It's really more likely your populated part is a large island (continent) inside a large sea that is being slowly reduced in size as the climate changes. It's a dying planet, maybe, and this the last inhabitable region ? $\endgroup$
    – StephenG - Help Ukraine
    Commented Oct 21, 2020 at 13:57
  • $\begingroup$ i dont quite get it, but isnt that basically what arab is? they are isolated by desert and build their civilization on oasis (not due to volcanic though as far as i know), and i mean the one that not part of silk road path, they are pretty much out of radar by other civilization until the rise of islam. $\endgroup$
    – Li Jun
    Commented Oct 21, 2020 at 15:12
  • $\begingroup$ @StephenG How does the sea survive? Where is it going to go? 10% of Earths surface water would be enough to cover the entire planet with a layer many hundreds of feet deep. I'm not counting chemically combined water or water deep below the surface. It might be dying but that's not the question. Assume it has enough life left in it for a few million years at least, the population have no idea what is beyond their area. That area is to the north west of a large shallow sea, the prevailing winds blow across the sea to a mountain range where it rains. The rain returns to the sea in rivers. $\endgroup$
    – Slarty
    Commented Oct 21, 2020 at 16:04

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Your planet is already like this from your description.

Let me explain. An Earth-clone with way less water, but everything else the same, will be missing the oceans CO2 reservoir. The 38 Tetratons of CO2 will instead be in the upper atmosphere.

To limit Global Warming to 2 degrees, we have to emit no more than 2.9TetraTons of CO2

You have a global warming hellscape already. Your planet is very very hot, but there aren't the storms that earth would get, as there isn't as much evaporation.

I don't know exactly where the weather would be mildest, but it will be cool near the poles. Antarctica has potential to be nice a temperate region.

Your 1000km square is a patch at the south pole. Could be nice, with a nice big lake and such, and then deserts for the rest of the planet where the oceans currently are.

There would be an equivalent temperate zone at the north pole, but with no lake, there will be no evaporation. No evaporation means no rain, so it's just a colder desert.

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    $\begingroup$ How would the lack of water vapor effect the climate, water is the best greenhouse gas. $\endgroup$
    – John
    Commented Oct 22, 2020 at 13:19
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It seems to me that the easiest way to ensure that this happens is to limit things essential to cross desert travel.

Water

Perhaps, the only oasis is centered in the desert and this is where your populace lives. The lack of water throughout the rest would ensure that you would be isolated while it is still possible to survive in the center.

Mounts

Perhaps, there are no mounts suitable for long distance travel so all travel would have to be on foot. This would severely limit the range that you can travel due to not being able to mass haul supplies.

Cultural

Those that leave never come back. Whether they find paradise on the other side, cannot trace a path back to the village, or die. The social implication is that if you wander too far from the settlement that you will never be seen again.

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The question boils down to whether you can have a habitable planet with so little water.

It seems there has been some simulation of what desert planets would be like. I found a paper on "land planets" that argues they would have a wider habitable range than Earth-like "aqua planets", because water vapor is itself a greenhouse gas. See here: https://pubmed.ncbi.nlm.nih.gov/21707386/

Wikipedia also claims a minimum 1% humidity is needed to keep the carbon cycle going: https://en.wikipedia.org/wiki/Desert_planet

So a planet with 10% the surface water of Earth is probably viable in that it could retain that surface water at an Earth semi-major axis around a sun-like star, but it wouldn't necessarily support the same kind of lifeforms that our planet supports. I would expect the biodiversity to be lower, just as biodiversity is higher in hot highly humid regions on Earth.

If there was so little surface water, the planet would necessarily be a series of giant lakes surrounded by colossal deserts. On Earth when there was a single continent Pangea, the inner regions were so far from the ocean that they became vast desert lands. On this planet with so little water, much of the land would be far away from small clusters of inland seas, so it seems plausible that a number of regions could be isolated by deserts, and be sustained by an inland sea/lake/etc.

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  • $\begingroup$ on the low end I doubt there would even be lakes, sediment holds 3-4% of the water on earth. $\endgroup$
    – John
    Commented Oct 22, 2020 at 13:17
  • $\begingroup$ @Axion Yes I’m thinking that 10% might be too much, that would be enough for 36 Mediterranean Seas worth dotted around. But with John’s comment about sediment, can’t put it too low, perhaps 5%. Enough for at least 3-4 Med’s worth plus sediment etc. Or maybe 8% giving 5-6 bigger deeper sea areas. $\endgroup$
    – Slarty
    Commented Oct 22, 2020 at 15:46
  • $\begingroup$ @Slarty - There could be one bigger sea on one side of the planet and then a gigantic Mega-Pangea with just a few smaller seas dotted in it. The civilization could be located around one of those but then have 1000s of kms of desert around it before any other large bodies of water are encountered. If they are pre-industrial, they might not be able to cross that large a desert easily. $\endgroup$
    – Axion
    Commented Oct 22, 2020 at 16:17
  • $\begingroup$ @Axion yes there are a number of interesting possibilities. I was thinking that even with a large sea winds blowing across it might pick up moisture, but either not pick up enough or what they did pick up might be widely scattered as rain down wind in desert floods that eventually just evaporate. My civilization will live near a sea to their south east and mountains to their north east. So most of the moisture from the sea ends up as rain in the mountains and flows as rivers back to the sea. But I feel another question coming on... $\endgroup$
    – Slarty
    Commented Oct 25, 2020 at 14:29
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Cold desert world and giant impact crater/s.

Your planet was very similar to Earth during its pre-history with an abundant ecosystem and plenty of water, though perhaps with a smaller iron core and less tectonic activity. Unfortunately it also had a moon that unlike Earths, was approaching its Roche limit.

When it finally reached this point the inevitable happened and it broke apart. What followed was a series of impact events ranging across all sizes up to dino killers and bigger which began to bombard the surface. The continual bombardment, over many decades/centuries/millennia results in a prolonged ice age which traps most of the water at the poles and permanently changes the planets albedo so very little if any of that ice ever melts.

Today you have vast icecaps at the poles and a much colder climate overall with very little liquid water ever reaching the temperate zone and what does is transitory or seasonal i.e. too little to support more than a few desert adapted plants, animals & insects.

Except for at the equator where one (or more probably a series of overlapping impact craters) have eroded and filled with water.

These craters served as a bio-refuge for many species of higher plants and animals including a species proto-intelligent omnivores.

A few hundred thousand years and you have your species confined to the slopes and flats around the crater seas, with the high ranges around the edges helping to prevent evaporation and/or fortuitously catching whatever moisture there still is being carried in the atmosphere to refill the those seas.

Your species is trapped. Unless there are other suitable crater lakes somewhere? But how to find them before you die of thirst or starve?

Plus as a bonus your planet how has a ring (of sorts).

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Welcome to Arrakis!

The planet you speak of is dry but for some oasis' and it has life? Well, let's make sure that it has no water on the surface. But this also leads to the fact that it can't have developed any life that is water-based on its own. No, let's skin the cat a different way and have the planet turn desert only after some point in time.

The pre-historic Arrakis

Before people were there, the planet had a mixed surface. It was quite flat, but there also had been quite more water, creating an expansive band of rainforest around the equator. In it, people developed over the generations. But then the He-under-the-sand arrived in the north desert, possibly by a comet strike. Nobody noticed at first, but over eons, Father Eternity did change the climate slowly as his children spread over the pole.

Desertification

Shai'Hulud consumes water from the surface: instead of excreting water, they excrete a hard substance called Melange. But as he grows and gets older, at some day he dies in the deep strata, leaving the water he had gathered there. As his body decomposes, the water is reintroduced to the deeper layers of the earth, creating water veins.

Arrakis as we know it

Over ten thousands of years, the water got stolen to deep earth, and the planet underwent desertification. People developed culture and started to cope with the dwindling ecosystem as The Makers prospered. The last remains of the old rainforests are oasis' that are protected by sitting on bedrock and not on the sand like the rest. Even those are shrinking as their water supply is drained underground and into the atmosphere slowly.

It will take the invention of deep pumping to secure those oasis' by replenishing their water from the deep strata, but for the time they exist.

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