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The surface of Mars has vast quantities of dust. It is everywhere. Even hard rocky areas are covered with dust.

I am aware of the mechanisms for dust formation, including wind velocity abrading rocks, biological actions, freeze/thaw cycling, and water flow. I am wondering how all the dust was generated on Mars? The wind seems at low velocity and low density and would, perhaps, be insignificant compared to earth. Perhaps it was water flow in past rivers that are now dry.

If anyone with knowledge of dust formation mechanisms and what would be the prominent ones on Mars would care to comment, it would be appreciated.

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    $\begingroup$ This is an interesting question, given that dust from space, entering the martian atmosphere should evaporate. Hence the dust must be produced in-house. I would strongly suspect seasonal erosion to be responsible for this, but unfortunately can't give a source. $\endgroup$
    – AtmosphericPrisonEscape
    Commented May 16, 2021 at 22:14
  • $\begingroup$ Related: astronomy.stackexchange.com/questions/28745/… $\endgroup$
    – Nilay Ghosh
    Commented May 17, 2021 at 11:10
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    $\begingroup$ Well, the maid only comes in once every billion years. $\endgroup$
    – A. I. Breveleri
    Commented May 17, 2021 at 14:28
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    $\begingroup$ Consider the White Sands desert in New Mexico (en.wikipedia.org/wiki/White_Sands,_New_Mexico#The_desert). If you give geology and weather enough time, things happen. $\endgroup$
    – Flydog57
    Commented May 17, 2021 at 18:09
  • $\begingroup$ I'm surprised nobody mentioned meteorite impacts. Maybe not a major source, but surely not negligible, either? $\endgroup$
    – Lawnmower Man
    Commented May 17, 2021 at 19:49

3 Answers 3

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As you pointed out, Mars has been without bodies of water for at least a billion years which had been used to trap windblown sediments and materials. Scientists believe that the dust on Mars formed through the weathering of rock through winds. Although the density of the atmosphere on Mars is 1% that of earth, its gravity being roughly 38% that of Earth's results in particles being able to move a lot farther each time it is picked up by wind. As a result, these windblown particles then chips off other tiny pieces of rocks and exponentially grows as those particles can be used on other rocks. Each collision that occurs grinds the particles of rock down until they are around 3 micrometers in diameter. However you may then ask why it isn't dustier; this is likely because historically, Mars may not have had enough of an atmosphere for the wind to make dust.

Source: Arizona State University

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    $\begingroup$ Temperature changes between night and day caused dust too. $\endgroup$
    – Uwe
    Commented May 17, 2021 at 8:55
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    $\begingroup$ How can a temperature change generate dust? $\endgroup$
    – spikey_richie
    Commented May 17, 2021 at 13:42
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    $\begingroup$ Expansion and contraction due to heat levers the rock apart mechanically, though this is very SLOOOW. $\endgroup$
    – Chris B. Behrens
    Commented May 17, 2021 at 15:43
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    $\begingroup$ @spikey_richie A temperature rise causes expansion of Marsian rock. The surface of the rock gets hotter than the core, therefore the surface expands more than the core. Rock is brittle, not elastic or plastic, the differential expansion causes fissures and cracks. Many temperature cycles over a long time generates dust from fissures. $\endgroup$
    – Uwe
    Commented May 17, 2021 at 20:43
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    $\begingroup$ Ice forming in pours, can open cracks, then ice forming in cracks, splits rocks apart, then more surface pours where ice can force more cracks to open. $\endgroup$
    – jwdonahue
    Commented May 17, 2021 at 22:22
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Just to add to @und3niable's answer, the erosion is not uniform, and this article based on this paper claims that almost all of the dust on the surface has the same chemical compisition and ratio, which matches that of the Medusae Fossae Formation. From Wikipedia:

The Medusae Fossae Formation is a soft, easily eroded deposit that extends (discontinuously) for more than 5,000 km along the equator of Mars. It has an area equal to 20% the size of the continental United States.

The paper proposed the MFF had been created by:

explosive volcanic eruptions, which would make it the largest known volcanic deposit in the solar system, by two orders of magnitude. Similar terrestrial deposits contain significant amounts of sulfur and chlorine, and the scientists found this was true of the Medusae formation as well.

The article goes on to say:

The researchers calculated how much of the formation has been scoured away over the last 3 billion years. They concluded that enough fine, powdery rock has been eroded to cover all of Mars in a layer from 2 to 12 meters thick . . . enough to convince Lewis and his colleagues that the Medusae Fossae Formation is, indeed, the primary source of dust on Mars.

As a separate source, the paper "Weathering, erosion and landscape processes on Mars identified from recent rover imagery, and possible Earth analogues" also goes into detail about other forms of erosion, which may contribute to dust, such as:

  • Insolation
  • Exfoliation
  • Honeycomb weathering
  • Weathering rinds
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It's not the presence of dust-forming that is the main cause, it is the utter absence of dust-removal factors.

On Earth, once a bit of dust is made, it is almost immediately snatched up by water, made to bond with surrounding dust, and renamed "dirt". Sometimes even "mud". And if it gets packed in with enough other dust, then eventually the whole region is subducted into the mantle, and everything gets melted and recycled.

On Mars, once a bit of dust is made, it just .... blows around making more dust.

The only way for dust to hide on Mars is to cover itself in more loose dust. And this does not destroy it, or change its nature. It is just kept immobile for a bit. If for whatever reason it gets uncovered, it is immediately again a speck of dust that is fine enough to be wind-blown. Even the occasional water or CO2 frost does not help at all. It may cover the dust for a bit, but will soon heat up, sublimate away, and actually waft the dust into the air in the process.

On Mars,

  • there is no liquid to bind to the dust.
  • there are no oceans that will happily accept megatons of dust and form sediment.
  • there is just too much atmosphere to allow the dust to vacuum-weld itself to other dust, as good self-respecting Moon dust can do.
  • there is no tectonic activity to recycle dust over the billions of years.

There's not even the chance of a bit of lava covering up the dust!

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    $\begingroup$ This does not answer the question. OP is asking how the dust came to be in the first place, not how it remained so. $\endgroup$
    – AtmosphericPrisonEscape
    Commented May 18, 2021 at 1:19
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    $\begingroup$ While this answer doesn't answer the question, it does provide additional useful information regarding reason for the vast amount of dust on Mars. $\endgroup$
    – Fred
    Commented May 18, 2021 at 9:34
  • $\begingroup$ @AtmosphericPrisonEscape the op asked "What caused all the dust on Mars?" and this is most certainly an answer to why mars has so much dust. +1 $\endgroup$
    – eps
    Commented May 20, 2021 at 1:12

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