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I have a planet covered with a large shallow ocean, which extends over most of its surface. I want to turn this planet into a great desert, specifically a salty desert (the salts of this desert are a mixture of several chlorides, not just NaCl, there is also NH4Cl, MgCl2, CaCl2, etc.). On Earth there are small salty deserts (salt flats), which form when a lake evaporates and leaves behind all the salts that were dissolved in it. I wanted to do something similar to form the salty desert of my planet, but the question is, where will all the water go?

The surface, which is completely covered by large amounts of salts, must be depleted of water, since it would dissolve the salts in one way or another (with rain, for example), which I do not want. What mechanism could I use to remove all the water without affecting the salts?


Keep in mind that I don't want to eliminate the atmosphere (as happened with Mars) or add greenhouse gases to increase the average temperature of the planet and keep the water always evaporated in the atmosphere. Freezing the water and depositing it on the surface is not an option either. Sending the water underground is a good idea, but you should find a way not to send the salts too. It would also be possible to add some compound that reacts with water and depletes it. Things like that.

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    $\begingroup$ Turn it all into sugar through photosynthesis? $\endgroup$ – Muuski Oct 9 '19 at 21:52
  • $\begingroup$ @Muuski I forgot to mention that the planet is devoid of life. $\endgroup$ – URIZEN Oct 9 '19 at 21:59
  • $\begingroup$ So, was it a conscious entity that put the water into an escape trajectory, or a natural process? $\endgroup$ – Muuski Oct 9 '19 at 22:10
  • $\begingroup$ @Muuski A natural process (geological, chemical, etc.). $\endgroup$ – URIZEN Oct 9 '19 at 22:15
  • $\begingroup$ Are you sure you want to exclude freezing? An ice-age that leaves all the water in very thick ice sheets at the poles could give you a really big salty desert. $\endgroup$ – Patricia Shanahan Oct 10 '19 at 1:12
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Answer is very simple: Glacial Period. Most of the water would be captured in polar glacials, while at equator it would be very dry, extremly hot at daytime desert.

There were such a situation on Earth during (last) glacial period (our oceans are to deep to dry out, but some water bodies did).

UPD: There still be rivers flow from glacials wich will bring minerals with them. If there are vast shallow bassins, where this rivers will flow, they will form vast salt deserts in mid and low-mid latitudes, exactly as you want it.

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  • $\begingroup$ Note if the planet is similar to earth you can't freeze most of the water without covering the entire planet in ice. you don't get a salty desert you get an iceball. $\endgroup$ – John Oct 10 '19 at 10:33
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    $\begingroup$ Note that freezing was specificaly excluded by the OP $\endgroup$ – Slarty Oct 10 '19 at 13:28
  • $\begingroup$ @Slarty, yes, I know. But this is the only way of mass desert creation that we realy have in our reality. Even Mars has polar caps (with water). Venus has no cups, but no deserts. Water is so common in our Universe, that having Earth-like planet without large amounts of free water in some form is completly unrealistic. And question is marked as science-based. $\endgroup$ – ksbes Oct 10 '19 at 13:48
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Earth has a lot of water because it is made from the remains of old stars that spit out tons of Oxygen and Hydrogen. If your planet is in a star cluster where none of the right stars have ever exploded for there to be much Oxygen, there would not be water in it's makeup.

So at first, your planet is just a boring, dry as a bone world. Then one day it collides with a massive comet from a distant star cluster where water is plentiful. It explodes leaving a shallow ocean over parts of the planet and introduces large amounts of CO2 into the atmosphere. The carbonic acid needed to dissolve the salts forms as the rain water falls through that CO2.

This brings up one minor issue with your planet which is that ocean salts come from acid rain hitting land. Your world can not be completely covered in salty deserts, but they could cover a large % of the world.

On Earth, the water that slowly sinks into the ground is being spit back out just as fast by volcanoes, but on this world volcanoes don't spit out water because there is none in the mantle. This means that after some time frame, the water left behind by the comet would mostly dissipate into the ground. There would still be water on the planet, but by the time it is done defusing evenly into the planet's interior, surface water will be just as scarce as any desert.

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  • $\begingroup$ It is a good idea, but if there is not enough oxygen to form water in large quantities, there will be less to form silicate minerals, carbonates and oxides... and the salts of the planet come from the dissolution of these minerals. $\endgroup$ – URIZEN Oct 10 '19 at 1:44
  • $\begingroup$ @URIZEN That is a good point. However, a comet carrying large amounts of water should also have large amounts of CO2. Amended my answer accordingly $\endgroup$ – Nosajimiki Oct 10 '19 at 14:32
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One option would be to have an huge geological formation that formed a completely closed bowl with mountains on all sides a little like the ring of fire but on a smaller scale perhaps a few hundred - a thousand miles across. This could be in a remote but wet area.

Over time this area would fill up with rain water to form a very deep wide inland sea and the rest of the planets shallow oceans would be depleted of water.

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    $\begingroup$ You may want to check my math but...The volume of the Earth's ocean is approximately 1.35 billion cubic kilometers. A hole with a thousand mile radius covers about 8 million square kilometers (The size of Canada), which means it must be another 125 kilometers deep to hold the world's ocean. (a third of the thickness of the atmosphere and 40% of the mariana trench) $\endgroup$ – Muuski Oct 9 '19 at 22:33
  • $\begingroup$ OP said the starting ocean would be shallow. $\endgroup$ – Nosajimiki Oct 10 '19 at 0:31
  • $\begingroup$ I do not uderstand why rain would prefer this enclosed region and not all the other area of the planet. Described formation is most likely to form deserts in the middle - not a sea (see Sahara or Death Valley). "A completely closed bowl with mountains on all sides" will not allow any wet air inside at first place. $\endgroup$ – ksbes Oct 10 '19 at 9:59
  • $\begingroup$ It wouldn't prefer the enclosed region, but if clouds can get in water will build up in that area at the expense of the rest of the planet as it won't be able to get out again. Cloud access depends on mountain height and winds. $\endgroup$ – Slarty Oct 10 '19 at 22:04
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Does the entire surface of the planet need to be desert, or just most of it?

If your world with a shallow ocean experienced some form of massive, sudden continental shift that then formed one very deep ocean, in theory all of the water could over time evaporate from the shallow ocean and rain over the deep one. Of course there'd be some redistribution, but if you enclose your deep ocean inside a rim large mountains, it could cause a sufficiently contained localised climate that would keep most of the water there. And if that ocean formed in one of the colder regions of your planet, there would be far less evaporation there than on the rest of the world.

Even with all of that, it would still rain from time to time on the rest of the planet. I think it would be impossible for this to keep rain away forever. But it could create massive expanses of salt deserts that experience rainfall less than once a year, and probably less than once a decade if you force the system enough.

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I don't think that you can get rid of the water without getting rid of the atmosphere. You just need a mechanism to replace the atmosphere.

Hit it with a big enough rock.

Theoretically Earth was an ocean world before it was hit by a rogue planet about the size of Mars. A lot of the lighter stuff was blown out at or above escape velocity. So that blew off most of our ocean (or all of it and it was then repopulated via comets). If the strike happens after most of the planetary afterbirth has been swept up or kicked out by other planets, you would end up with a dry world. Out gassing from volcanoes may be enough to restore an atmosphere (or just one or two comets after the big hit).

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  • $\begingroup$ Almost 80 % of the composition of volcanic gases is water vapor, therefore, if the atmosphere is replenished with volcanic gases after the impact, there would be a large amount of water vapor in it, which will condense on the surface forming an ocean again. $\endgroup$ – URIZEN Oct 10 '19 at 0:19
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If for some reason you have a lot of alkali metals or alkaline earth metals (maybe underground deposits that at some moment get in contact with the water), water will react with them to form a hydroxide and H2, which in turn can escape from the planet. You will need a lot of them, though.

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