I'm developing a world based on a terraformed Mars, which was cut off from interstellar society and regressed to a pre-industrial level of technology. Mars has an ocean, but most of the settled people live in craters, since this is where almost all the arable farmland exists. My explanation for this is that the Martian regolith is sandy and therefore porous, and the only place this is not true is craters and places where rivers and lakes previously laid down impermeable beds of clay. In addition, the crater floors are closer to the water table. In between, the land is a 'wet desert', where mosses and other simple things can grow but otherwise the rain drains too quickly to allow for trees etc. In these plains, nomadic herders scratch a living from animals specially adapted to eat the sparse moss and / or lichen.

My question is: how realistic is this? Could porous regolith prevent plant growth, but allow for lichens and / or mosses? How quickly would soils form in highland regions from whatever plant life there was? Is there any other way I can justify arable farmland being limited to isolated craters and floodplains? Also, how much and where would impermeable lava flows also allow for a raised water table? What might coastlines and rivers look like - also arable?

Thanks in advance, WH

Edit: I realise mosses aren't necessarily what would would grow in place of trees, I just mean some small, sparse plant-life that would grow in land that wasn't arable, but would potentially feed some sort of nomadic herd.

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    $\begingroup$ Have you had a look through Space Exploration SE? you may find resources to answer your questions there & if what you want is real world info on Mars regolith its makeup & properties etc that may be a better place to ask : here's some links to some Mars related questions there ~ Cyanobacteria & Lichens on Mars ~ How far down can we dig. $\endgroup$
    – Pelinore
    Commented Apr 5, 2020 at 22:42
  • $\begingroup$ Welcome to worldbuilding . Please take the tour and when you have some free time read-up in the help center about how we work, whilst you're at it, you will see the that we deal with one question at a time here. Please edit yours down to a single question. We encourage you to post further questiions in seperate threads. $\endgroup$ Commented Apr 5, 2020 at 23:05
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    $\begingroup$ Mars has an ocean then it was some long time after Mars was terraformed, it already has a non-trivial atmosphere and so on. Which makes it plausible for the regolith to no longer be a fine dust by coalesced into bedrock - got rid of its perchlorates, with the chlorine in the calcium salts washed as more soluble salts (sodium) and replaced by calcium carbonate resulted from the thawed carbon dioxide in the soil. I don't think your 'wet deserts' are realistic at all. $\endgroup$ Commented Apr 5, 2020 at 23:08

1 Answer 1


Terraforming is part of your premise.

And part of your answer.

If the terraforming process involved dragging large asteroids and making them impact mars, the craters could contain glass. That would solve your porosity issue.

Would create bowls where you can farm and deposit your organic matter.

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    $\begingroup$ Thank you for your response Gustavo. However the issue is not too much porosity in the craters - I think this is adequately solved by clay deposits and lava flows - it's creating high porosity or some other obstacle to life outside of the craters. It's been pointed out that after a relatively short time where a hydrological cycle exists, soils would probably form, reducing porosity and allowing life to develop in most places. $\endgroup$ Commented Apr 24, 2020 at 15:22
  • $\begingroup$ Fair enough missed the goalposts then :-P $\endgroup$
    – Gustavo
    Commented Apr 24, 2020 at 17:36

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