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One potential solution to an initial permanent colony on Mars would be a series of modules with dirt floors and walls and slightly convex, transparent roofs. Assuming the interior temperature was artificially maintained at a human comfortable 22 C, it would take significant time for the walls and floors to come close to thermal equilibrium. However, once they did, they would provide nearly infinite thermal insulation on all sides, except the top. Their large thermal inertia would also be helpful in mitigating Mar's large diurnal temperature cycles. Lastly, they would block the constant bombardment of galactic cosmic rays (GCRs) on all sides, except the top.

Considering these aspects, the idea of human habitat modules built with dirt floors and walls (possibly covered with some sort of masonry) seems worth exploring further. The problem is, what we think of as dirt on Earth, usually contains a significant component of organic detritus. Assuming the existence on Mars of regolith, sand, clay, and bedrock, if you tried to dig a big hole, what would you be digging in? It would seem that a combination of sand and clays as a dirt, or dirt substitute, could be structurally sound. So my question is: is there dirt or its equivalent on Mars? Maybe a better question might be "How can you create a large, deep hole in the ground on Mars?".

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  • $\begingroup$ You already know there is dirt on Mars, so I think your question is wrong. I think what you really want to know is what the best composition of the soil would be to create a large, deep hole. Am I right ? $\endgroup$
    – Cornelis
    Jul 31 at 14:10
  • $\begingroup$ Considering the +12/-0 votes, the excellent, direct and highly up-voted answer (+15/-0) and the simplicity of the question itself; "Is there dirt or its structural equivalent on Mars?" along with a clear explanation of what that means in context, I don't see how closing this question and blocking further answers could possibly be a good thing. voting to leave open. $\endgroup$
    – uhoh
    Aug 1 at 0:02
  • $\begingroup$ @uhoh I agree with you. Considering the excellent upvoted answer and the large number of comments, this seems to be a subject of interest to many that should continue to be explored. $\endgroup$
    – Vince 49
    Aug 1 at 0:16
  • $\begingroup$ @Vince49 the single close vote is for "Needs more focus; This question currently includes multiple questions in one. It should focus on one problem only." I don't see how this can be further focused. Does 'Mars dirt' work similarly to 'Earth dirt' when digging holes or making earthen structures? seems perfectly focused to me. I can't see how it could be divided into multiple questions. $\endgroup$
    – uhoh
    Aug 1 at 0:32
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The fine regolith on Mars is regarded as being the closest equivalent to an Earth like soil. It contains sand and dust. Clay deposits have been found. The two could be mixed to produce a more graded material with moisture retaining properties.

Technically martian soil is not dirt, but some may refer to it as either dirt or soil. If differs from soil on Earth because no martian soil has yet been found to contain biotic materials, such as humus and microbes. Additionally, most martian surface soil lacks water.


Edit following questions in comment to the first version of this answer.

Earth and Mars have had different geological histories. At one time water was present on the surface of Mars, now it is not. Earth has had a longer history of water in its surface and this is one of the reasons for the differences in geological history.

Water still plays an importance role in shaping Earth geology, as does weathering. Much of Earth's soil is the result of weathering: heat, water - rain, rising and falling water table, ponding, submersion, desiccation, rehydration, ice, chemical reaction with atmospheric gases, with liquid acids, microbial activity. Earth also has plate tectonics and volcanic activity.

All these continually renew the surface of the Earth. Mars lacks much of this. The renewal of it's surface is significantly slower and different to Earth's.

Like the Moon, meteorite impacts have a significant affect on martian regolith. When a meteorite impacts Mars, a crater is created and material is ejected from the crater. The size distribution of the ejected material varies from dust sized particles to clasts that can be boulder sized. All this gets mixed up and is part of the regolith.

It may be possible to find regions where the upper part of the regolith resembles a dry version of soft Earth soil that is easily dug with an excavator or shovel. Apart from sand dunes, I would expect most martian regolith to be a varied mixture of particles ranging in size of silt to boulders, much like stone deserts on Earth.

If you want to get something like a "soft soil" on Mars some preparation might be required. Dig up a lot regolith and use mechanical screens to sort the material into stockpiles of material of different sizes. Mix the small size materials into a uniform mix and backfill the hole.

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  • $\begingroup$ Fred thanks. It hadn't occurred to me that there might be a Wikipedia entry on that. How is fine regolith different from sand? I ask because, if I tried to dig a deep hole in dry sand, the sand would flow to fill up the hole. It seems that there would need to be something to hold the bits together to make digging a deep hole practical. Maybe my question should have been something like "Is it practical to dig a large deep hole on Mars without the sides of the hole flowing to fill it up?". Let me know if you think that would be a better question. $\endgroup$
    – Vince 49
    Jul 29 at 16:15
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    $\begingroup$ @Vince49 Mars dirt does not dig well, this can be seen by the typical angle of the Mars dunes, which is composed of the same material minus significant rocks. Ont he other hand, Mars soil with even a tiny bit of water in it, which might possibly be the "normal state" for dirt below the immediate surface, is like a weak concrete, and quite diggable. Think a very dry variant of permafrost. Besides, if there is not enough water, you can add your own. Even 5% water makes regolith a very cold-compactible material. Or use hot sintering (~500C or so) which produced a decent fired-clay type surface. $\endgroup$
    – PcMan
    Jul 29 at 17:26
  • $\begingroup$ @Fred thanks for the useful additional information. $\endgroup$
    – Vince 49
    Jul 29 at 17:36
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    $\begingroup$ Took me a while to realise that humus is not the same as hummus. I was very confused wondering why anyone would be looking for hummus on Mars. $\endgroup$
    – Rob
    Jul 30 at 13:25
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    $\begingroup$ Note that regolith is not dirt or soil. Dirt is regolith plus a lot of organic material. But this is a good answer. $\endgroup$ Jul 30 at 16:07

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