My world takes place on a desert planet, but there is a small habitable forest with water and life. My main inspiration for this is Halem'no from star trek, but without a weather tower sustaining the life. I just am wondering if this is possible, and if there is a specific condition because of a moon or the axis tilt that could make this work.
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13$\begingroup$ For future reference, "is this possible?" (or any other form such as "is it feasible?") is the wrong question to ask here. This isn't Physics or Astronomy or Earth Science. As stated in the help center, our goal is to help you build an imaginary world. "How can I rationalize?" is the question you should be asking and the expectation you should have concerning answers. $\endgroup$– JBHCommented Jul 4 at 2:46
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3$\begingroup$ It's also worth noting in the question whether the planet has been like that all along, or become that over time. $\endgroup$– Escaped dental patient.Commented Jul 4 at 3:47
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7$\begingroup$ @JBH A handful of contributors have decided to aggressively gatekeep this site, pushing out reasonable and interesting questions on technicalities, and then using their successes as precedent to narrow the window even further... Could you help out with standing against this unfortunate trend, and making the site more welcoming? $\endgroup$– JedediahCommented Jul 4 at 12:19
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2$\begingroup$ Desert as in sand desert? Snow desert? Semi-desert like tundra? Or just not quite hospitable like very mountainous areas or... the open ocean, with a single island in the middle? $\endgroup$– jcaronCommented Jul 4 at 22:48
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2$\begingroup$ @JBH Even in legal theory (in the US and UK, at least), precedent and sometimes common sense have a place alongside the rules. The recent shift to a tighter enforcement on the "let's make stuff up" stack flies in the face of historical precedent... And, um, traffic cops being asked for lenity is pretty normal. $\endgroup$– JedediahCommented Jul 5 at 10:45
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6 Answers
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How about a very deep rift valley?
The surface could have a thin atmosphere, and continuous illumination from a cloudless sky. It would be hot and dry in the day and freezing at night, and the air could be too thin to breathe. The valley floor could be cooler and in shadow, but with enough light reflecting from the valley walls to see by.
The Vallis Marineris is 8 Km deep at its deepest point. A valley that deep could have a normal Earth atmosphere at the bottom, and the rim would be at the 'Zone of Death' where the air is too thin for humans to survive for long.
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$\begingroup$ You still need to explain where all the water comes from. Evaporation will occur in the scenario you describe (at least during daylight hours). It might be at a very, very low rate but it will occur and the cumulative effect would see moisture from the valley carried away in the local winds and dispersed planet wide. Where does replacement water come from? The obvious answer is underground springs fed by subterranean basins. But again on a desert world where did that water in the basins come from? $\endgroup$– MonCommented Jul 5 at 12:11
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$\begingroup$ My first thought was a Mars like world to BTW. But that sought of leads to the oasis being the last vestigial location of life on the planet. This is because you have to assume complex life developed and evolved more widely on the surface & slowly ended up retreating to the valley as the surface dried out, leaving a rudimentary ecology of tough lifeforms on the valley floor. (The valley itself not being large enough to sustain the evolution of large complex ecology's like we see on Earth.) And there's still not going to be enough surface area down there to maintain Earth like oxygen levels. $\endgroup$– MonCommented Jul 5 at 12:26
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$\begingroup$ @Mon I don't see a problem with water. You might have a shallow sea at the bottom of the valley. The air at the valley edge will be cold and have very little water vapour. If the wind blows along the valley, the cold air would descend, and be very dry. The warm, wet air would drop its moisture as it rose at the other end, giving rivers or glaciers that bring the water back into the valley. Think of the weather in Chile: the winds may blow from the Pacific, but very little moisture makes it to the Atacama desert. $\endgroup$ Commented Jul 5 at 14:17
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$\begingroup$ Little is not none (re the Atacama desert), There has to be a replacement source of water for the depression/valley. The problem remains how the question is framed i.e. a more detailed description of the world is required that allows for some kind of a water cycle which leaves most of the planet dry(ish) most of the time is needed e.g cold desert biomes with large icecaps and seasonal weather? An impact crater or something on a formerly wet/verdant world that underwent catastrophic environmental change after life evolved with simple remnant lifeforms hanging on in the valley? $\endgroup$– MonCommented Jul 6 at 1:22
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Nile River
Have you seen a satellite photo of the Nile River? It is basically a small stretch of very green "forest", surrounded by very harsh deserts.
Your world could be very old, with very little water, with small lakes/oceans so saline that life is not possible on them, but with enough water cycle to maintain non-saline rivers that sustain life.
Bonus points if your small habitable forest is sustained by an underground features that gets refilled by a non perennial river, but the river bed itself is too dry in general to sustain life. (See the small "leaf" forest, outside river course bellow.)
Credits: https://www.over-view.com/
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6$\begingroup$ Your only problem? The Nile river doesn't exist on a 'desert world'. Yes, it travels THROUGH a dry/arid region but the actual source of the Niles (White and Blue) are the vast tropical rain forests, great lakes and well watered highlands of tropical Africa. In this scenario? There are no vast tropical rain forests or highlands. Neither are there the monsoonal weather patterns that sustain them or the oceans from which those monsoonal weather have to originate. Where does the water come from? $\endgroup$– MonCommented Jul 5 at 12:03
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$\begingroup$ Also, if you had a body of underground water refilled from outside without draining into something else, it would gradually fill with salts and/or minerals and become a new Dead Sea. $\endgroup$– DWKrausCommented 2 days ago
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Probably not.
Your problem is oxygen. On Earth all but the most minute fraction of oxygen is produced by photosynthesis. And to achieve the current level of oxygen in the atmosphere there HAS to be enough photosynthetic organisms on the planet to produce it because in their absence oxygen will bond chemically with other elements in the crust and the level of 'free' oxygen left circulating in the air and water would drop to near zero over time. (Don't know how long it would take but not long in geological terms.) And the thing is? All of those photosynthetic organisms will require access to water. So you need huge volumes of liquid water maintain current O2 levels.
Simply Put? In your scenario there won't be enough photosynthetic life on the planet to produce the amount of O2 needed to maintain a breathable atmosphere. On Earth I believe something like at least half of the Earths O2 comes from the oceans and fresh water, the rest from the mass of plants etc covering it's surface.
You can see the problem. The oxygen has to come from somewhere. A truly desert planet doesn't mean there can't be any plants that produce O2 mind you but you also wont have any rain forests churning it out either, let alone oceans etc! So any inhabitants of your world will have to get by with a lot less oxygen in the air.
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3$\begingroup$ Oxygen is certainly highly important, but whether land based life is required is an open question. Photosynthetic bacteria first evolved in the sea ~ 3 billion years ago and produced vast amounts of oxygen that cleared the oceans of huge quantities of iron (as the oxide), after that started to outgas and oxidize the land crust. Multicellular land plants only arrived about 1 billion years ago. Perhaps sea based photosynthetic organisms could have eventually produced the level of oxygen that we see today, It may have taken longer. But less land also means fewer land animal oxygen consumers. $\endgroup$– SlartyCommented Jul 4 at 6:55
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3$\begingroup$ @Slarty The only problem is that the original post specifically stipulated that the world in question was a 'desert planet' i.e. unless otherwise stated it had no large bodies of liquid water (in proportion to it's total surface area). You see the problem. The author would need to specify that their world had oceans and seas in the past. And even then once those oceans etc freeze/evaporate? Sustaining any complex surface ecology becomes problematic. $\endgroup$– MonCommented Jul 4 at 9:59
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1$\begingroup$ Most deserts on Earth have some plants photosynthesising away and producing oxygen. With minimal animal life (in the desert, but also in the oasis because of its size) a reasonable level could be maintained with far lower production. The bigger problem on this planet is more likely to be getting even the little water they need to the desert plants - if there are no seas for it to evaporate from you'll have trouble. For that matter where does the water for the small fertile region come from? Ice caps provide one possibility, or hyper-saline (dead) seas $\endgroup$– Chris HCommented Jul 4 at 15:59
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1$\begingroup$ If a planet has 75% ocean and 25% landmass, the latter all desert except a wee bit of oasis, does it count as a 100% desert planet? If yes, then let the ocean produce all the oxygen you need. $\endgroup$ Commented Jul 5 at 13:08
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1$\begingroup$ @FrançoisJurain if it is 75% ocean it can't have the rest be desert, way to much water in the atmoppshere. $\endgroup$– JohnCommented 2 days ago
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While it is not uncommon to have some "green pockets" in an otherwise hostile landscape, it looks more challenging to have only one such a "pocket" over the whole planet. The causes and conditions behind this happening are more likely to occur in multiple locations.
The simplest way seems to tie the existence of an oasis with some unlikely event that only occurrs once. This may be:
- A meteorite falling or spacecraft landing at the location and bringing some elements that are otherwise not present in the needed amounts. This allows the local life forms that are normally very scarce and difficult to spot to grow in large numbers. For instance, selenium is an essential element, but only a few micrograms per day are needed by the human body.
- The life is slowly declining on the planet for some reason, and we catch the narrow time window with only the last oasis remaining (some place must be the last!)
- The catastrophic event caused the mass extinction of all life on the planet, but multiple favorable circumstances allowed this pocket to survive. Life cannot spread from the oasis if it is poorly placed somewhere in the middle of the desert, or the rest of the land may still be contaminated.
- There is some rare geological formation under the ground that is somehow useful and essential for the oasis to survive. Something like Yellowstone hotspot, even if I have no idea that the use it would be for an oasis from a supervolcano.
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Science: Put a lid on it.
You can't have what you're asking for as an open system, but there's no size limit to building a terrarium. Build a giant dome, cap a valley, or even just have a 30 meter high roof with lots of big skylights and pillars every few meters from horizon to horizon. You can have pretty much whatever climate you want inside.
Sci-fi Space Magic
The little-understood metabolism of Shai Hulud, great sand-worm of the infinite desert, is thought to be responsible for this planet's ecological peculiarities. File the serial numbers off of this one first.
The nanite swarm from the mysterious crashed space ship did it. But what else are they doing? And are the seemingly friendly and peaceful natives really humans at all?
The weather control system was supposed to keep it from raining on holidays by intercepting all the rain before it got close to the ground, shunting it through Q-space, and re-dispersing it in the upper atmosphere until it was time to let it rain. But it turns out that every day was a holiday, and what's worse, the weather control system thought that oceans, lakes, rivers, and aquifers were all rain. Fortunately, there was one small spot that had opted out of the weather control system because they preferred the thrill of adventure that comes of leaving home without an umbrella, so a remnant of humanity survived. Many heroes have set off on epic quests to find and destroy the weather control system and finally allow the water to reach the ground and re-hydrate the world, but so far, all have failed.
It just is. Sometimes the best solution is no solution.
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Tidally locked planet
Sure if you have a tidally locked planet, half the planet is too hot for multicellular life and super dry, half is too cold and likely covered in an ice sheet and there is a narrow band of green along the twighlight area. so you have hot desert on on side cold desert on the other.
Large part of the planet can still have unicellular life, so you have an oxygen source, you can even have small seas rsting up much of the habitable zone by changing elevation.
