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How did Mars get so dusty?

The Martian surface is littered with rocks, which I presume are from asteroids or other objects hitting the planet surface. But the red dust, or dirt that covers the planet surface...is that also an effect of impacting asteroids or other objects, or has the red dust always been a characteristic of the planet surface, created possibly by atmospheric changes or perhaps ancient surface features?

The dust on Mars could have been formed in many different ways. As you pointed out, impacts break up rock to form smaller particles, and they certainly contributed to the Martian dust. Dust can also be formed by wind abrasion, when particles carried by wind chisel away at rocks over time. Landslides will break up particles, as will chemical alteration of rocks exposed at the surface. If there was water on Mars, flowing water can also erode rocks and deposit fine-grained particles elsewhere. Volcanic eruptions can produce ash and dust as well. The Martian dust was probably created by some combination of these processes, and then mixed up over time by dust storms.

I don't think anyone really understands the history of Mars well enough to know how the volume of dust on the planet has changed over time. For example, was the planet this dusty 3.5 billion years ago? Does Mars get dustier over time, or has some of the dust/sand been cemented to form rock (as happens on Earth)? There are definitely more ways to create rock out of dust and sand on Earth, because water does this very effectively (the particles carried by water form clays and sandstones). On Mars, the current lack of water is probably part of the reason that Mars is so dusty. But I'm afraid I don't have a good answer as to how long the planet has been this dusty. If Mars had a wetter and warmer period in its early history, there may not have been much dust at the time, and the planet would have become dustier as it aged. But if there were only sporadic, 1000 year periods when Mars had a limited amount water erosion, then large amounts of dust may have been present on Mars over a lot of its history.

February 2004, Lynn Carter (more by Lynn Carter) (Like this Answer)

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