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Ah yes, ferrihydrite dust. Common rust.
Humans have been looking at Mars with our ocular spectrographs for millennia and saying "looks like rust". That's why Mars's alchemical symbol is the same as that for iron. Since the iron age, we have recognized that Mars is the color of oxidized iron. Mars is the symbol of our species's belligerent greed for metals. A whole planet of iron! Think what we could build if we could refine it in a forge large enough!
Turns out, we were right that whole time!
Did you read the article? We know it's rust, but there are many forms of iron oxide that form in different conditions.
Previous studies of the iron oxide component of the martian dust based on spacecraft observations alone did not find evidence of water contained within it. Researchers had therefore concluded that this particular type of iron oxide must be hematite, formed under dry surface conditions through reactions with the martian atmosphere over billions of years – after Mars’s early wet period.
However, new analysis of spacecraft observations in combination with novel laboratory techniques shows that Mars’s red colour is better matched by iron oxides containing water, known as ferrihydrite.
You know, that is an important clarification, thank you.
The water content in the rust and what that means for the formation conditions are really important and exciting!
I was trying to emphasize that the iron oxide part has been known for millennia. The technique of trying to compare materials based on their color is older than civilization, though our methods have gotten a bit more precise in recent centuries. I was trying to humanize the act of spectroscopy into something most people were familiar with. In doing so, I left out the discovery of water that made this new research so exciting.
The fact that there is also plenty of water in the dust is an important new discovery, both for understanding how the dust formed and for understanding the current water budgets and cycles on Mars. I wonder how easily that water gets exchanged between the dust, atmosphere, and subterranean reservoirs. I wonder how the dynamic distribution of water interacts with Martian weather, including its global dust storms and the large seasonal atmospheric pressure variations.
It's the ol' gaussian curve meme:
The missing part in OP's excerpt: It was previously assumed that the rust was hematite, which forms in dry conditions.
My completely unfounded theory is Mars’ iron core was puked out all over the ground and the water rusted it away. That turned her red and lost her magnetosphere.
Puked out, like from volcanic eruptions?
Yea. I have no idea if there is evidence of that or not. I never really studied Mars more than, “red planet.”
Mars's iron content is not that far off from the Earth's mantle. The name for this type of rock on Earth is "mafic", because of the magnesium and ferrous (iron) content.
On Earth, the processing of plate tectonics selects for iron-poor rocks within continental crust in favour of felsic (feldspars) silicates with a lower melting temperature.
Mars has no plate tectonics and therefore has a more primordial mafic composition.