From what I understand, Martian dust is primarily composed of iron oxide, which is one ingredient for a thermite reaction. If heated to the proper temperature, would aluminum (possibly powdered) react with the Martian dust to produce molten iron?

If so, would it be dangerous to have aluminum structures/tools on Mars?

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    $\begingroup$ Thermite is very difficult to ignite. From Wikipedia: "Ignition of a thermite reaction normally requires a sparkler or easily obtainable magnesium ribbon. These temperatures cannot be reached with conventional black powder fuses, nitrocellulose rods, detonators, pyrotechnic initiators, or other common igniting substances. Even when the thermite is hot enough to glow bright red, it will not ignite as it must be at or near white-hot to initiate the reaction. It is possible to start the reaction using a propane torch if done correctly." $\endgroup$ – Uwe Jan 14 '18 at 20:54

Probably not any more likely than on Earth. Actually, Curiosity's (MSL) rover's wheels are made out of aluminum and they've been grinding through iron oxide rust that gives Martian regolith and the whole planet its color for quite a while now. And Spirit and Opportunity (MER) rovers also use several tools, among which even grinders, made out of aluminum. So why this isn't a problem?

For thermite welding, you require very fine powder mixture of metal oxide and a metal that will act as a reducing agent when both are heated to a sufficiently high temperature to initiate the exothermic chain reaction. Very fine, often nano-sized aluminum powders are used for that, as it's a very strong exothermic reducing agent. Actually, nano-aluminum powders are often also used in rocket propellant mixtures as catalysts, or even on their own. A solid aluminum construction, or a tool made out of it, won't do.

Even less likely as aluminum also slowly forms a thin oxidized layer naturally (there is a bit of oxygen in Martian atmosphere too), or is protected intentionally such to give it a bit more surface strength, reduce its triboelectric potential, paramagnetism, or simply to additionally shield it against wear and tear.

What happens with thermite powders when sufficient heat is applied is, simplifying, that it excites individual granules to a point where metal oxide and reducing metal exothermically exchange oxygen atoms. This results in enough heat for surrounding, tightly packed granules that absorb this produced heat to continue the reaction on their own, setting off an exothermic chain reaction of sorts. For thermites with aluminum powder, this is called an aluminothermic reaction.

So you require not only all the ingredients and the heat to set the reaction off, but also a rather large quantity of such fine powders, well mixed and packed tightly together, so the reaction can be sustained. So, unless you've set that up intentionally, I don't see it happening spontaneously on Mars any more likely than it would on Earth. And it doesn't.

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    $\begingroup$ In addition to the need for fine,well-mixed powders and extremely high ignition temperatures, the Martian soil is nowhere near 100% Fe2O3. More like 10%, even in the richer regions. $\endgroup$ – pericynthion May 7 '15 at 1:50
  • $\begingroup$ Thought this must be the case! Glad my curiosity ended up catching this great answer! $\endgroup$ – Thane Brimhall May 7 '15 at 2:17
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    $\begingroup$ To give you an idea of how hard it is to ignite thermite, it's common to use burning magnesium as a "fuse" to provide the heat needed to get it started. $\endgroup$ – Mark May 8 '15 at 2:04

Iron, while abundant in weight percents only accounts for 2% iron in martian soil samples. This is not sufficient concentrations for a strong naturally occurring exothermic reaction.

And if you are interested in "local" sources of aluminum on the surface, it's about 10% but already in an oxidized form.

Soil Weights by Mission Mars Curiosity Rover

Source also see Inspecting Soils Across Mars

  • $\begingroup$ +1 I made an edit to your answer separating discussion of surface iron (the question) from surface aluminum, which seems to be an afterthought. Welcome to Space! $\endgroup$ – uhoh Mar 18 '19 at 8:32

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