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The Martian surface is known to have periodic 'dust storms'.

Depictions of Mars typically show poles with ice at the surface. If that is the case why are the Martian poles not blanketed with a thick layer of dust? Or is this depiction of ice directly on the surface inaccurate?

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    $\begingroup$ We have this question on astronomy.stackexchange.com/q/33461/16685 but the answers are rather brief. $\endgroup$
    – PM 2Ring
    Nov 6, 2023 at 9:08
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    $\begingroup$ The ice is fairly dynamic. From Wikipedia, "During each year on Mars as much as a third of Mars' thin carbon dioxide atmosphere "freezes out" during the winter in the northern and southern hemispheres". $\endgroup$
    – PM 2Ring
    Nov 6, 2023 at 9:12
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    $\begingroup$ @PM2Ring it is exactly same question. Possibly some one can raise a bounty to help get a proper answer. Meanwhile, I have put a link to that question as I can see there is an answer which is not "brief". $\endgroup$ Nov 6, 2023 at 16:11
  • $\begingroup$ I think the linked question isn't really the same; the author there acknowledges seasonable sublimation as an effect at the poles, and is asking about crater ice specifically. $\endgroup$ Nov 6, 2023 at 20:31
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    $\begingroup$ @11111 please use caution with your edits--adding "thick" may have changed the meaning of the question to one that the asker didn't intend. $\endgroup$
    – Erin Anne
    Nov 7, 2023 at 6:01

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Dust storm on Mars

The south pole of Mars with a dust storm over it.

Well, from these pictures, I think you can see that there is in fact a visible ice sheet at the poles, and you can see that global dust storms do in fact kick dust over the poles. Dust that blows into the polar region can also blow out of the polar region, but surely some of it gets stuck there. So how do the poles stay white?

The main reason is that the polar ice evaporates every summer and re-deposits every winter. The shiny white ice isn't just the same ice year to year, it's constantly melting out (or sublimating, really) and being renewed, transferring dust to the ground underneath, so what you see is always nice and shiny white.

Hubble got some nice photos in the mid-90s to show how dramatic the seasonal difference can be: Hubble images of Mars's north polar cap shrinking to almost nothing in summer

Even at the most extreme latitudes where the ice never fully melts, it thins in summer and thickens up in winter as the atmosphere freezes and deposits, and dust will accelerate the melting process. A patch of dust at the pole is less reflective than the ice around it, so it will heat up and melt its way below the surface level.

In large part, this is all very similar to how it works on Earth. When the sun comes out after a snowfall, if you place a dark object on the snow, it will rapidly melt a hole as it sinks down to grass level. Our own poles and permanently white mountaintops must be subject to a certain amount of dust and debris blowing in, yet they're always bright and shiny century after century. Surface ice comes and goes.

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    $\begingroup$ Even in dust storms the accumulation is usually very light. Dust particles on Mars are almost as fine as wildfire smoke particles. Some details about martian dust are in this answer, just the section titled "A Light Dusting" not the whole thing. $\endgroup$ Nov 6, 2023 at 21:34
  • $\begingroup$ I thought about bringing up the extreme lightness of martian dust, but it didn't seem relevant. Even a very thin dusting of it makes for a visible buildup on mars probes and rovers, so the same should be true of ice. $\endgroup$ Nov 6, 2023 at 21:47
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    $\begingroup$ Re "the polar ice (which is mostly carbon dioxide)": That can't be (my emphasis): "The caps at both poles consist primarily of water ice. ... Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, whereas the south cap has a permanent dry ice cover about eight metres thick." $\endgroup$ Nov 6, 2023 at 22:53
  • $\begingroup$ DarthPseudonym - I was thinking the ice may not be as smooth a surface as metal or solar panels, the ice itself being more of a dusting as far as I know, which might affect the dust's ability to build up a layer. And being thin the dust might be easier to be covered up by the ice that gets redeposited. $\endgroup$ Nov 6, 2023 at 22:57
  • $\begingroup$ @PeterMortensen Okay, fair enough. That sounds like a lot of dry ice to me, but I'll remove the parenthetical as it's not really relevant anyway. $\endgroup$ Nov 7, 2023 at 14:09

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