<p>A lot of the water ice on mars is covered with dust.  NASA's Phoenix mars lander only had to scrape off some of it to find the layer of ice underneath  as seen here: <a href="https://www.nasa.gov/mission_pages/phoenix/images/press/sol_020_024_change_dodo_v3.html" rel="noreferrer">https://www.nasa.gov/mission_pages/phoenix/images/press/sol_020_024_change_dodo_v3.html</a></p>

CC BY-SA 4.0
2019-09-25T23:52:13.013Z
I'm not implying that **all** ice is clean out in the open, I'm asking why the exposed ice is exposed.
SE - stop firing the good guys
CC BY-SA 4.0
2019-09-25T23:58:36.963Z
The Martian atmosphere is too thin for water to exist in a liquid state so the ice will just freeze directly to a solid and then evaporate back into a gas.  Usually this cycle follows the seasons, and if the ice freezes out in the winter and evaporates in the summer faster than it can get coated in dust, it just stays exposed throughout the Martian winter before evaporating.
Kyle
CC BY-SA 4.0
2019-09-26T00:22:21.790Z
To add, water ice is following the same seasonal sublimation process you outline in your question for CO2, similarly leaving a clean surface.
Kyle
CC BY-SA 4.0
2019-09-25T23:45:26.767Z
2019-09-25T23:45:26.767Z
Kyle
<p>One hypothesis:</p>

<blockquote>
  <p>at first there is a rapid decrease
  in albedo, which is then followed by a rapid increase. The
  decrease could be due to dust contamination after all
  the CO2 frost sublimation; as temperature continues to rise
  up, dust could thermally sink into the water–ice and/or fall
  into cracks between larger grains of water–ice<br>
  <a href="https://pdfs.semanticscholar.org/b05a/165a8047fb4ba9556d682c371b74455dfc57.pdf?_ga=2.5833207.578246397.1570243032-929020594.1570243032" rel="nofollow noreferrer">A conceptual model for explanation of Albedo changes
  in Martian craters</a>, p.889.</p>
</blockquote>

<p>Also, the <a href="https://earthsky.org/space/ice-ages-and-ice-at-mars-polar-cap" rel="nofollow noreferrer">north polar ice cap is slowly thickening</a>, by 70 microns per year, which might bury the dust.</p>

CC BY-SA 4.0
2019-10-05T03:27:18.293Z
2019-10-05T20:45:06.300Z
2019-10-05T20:45:06.300Z
Keith McClary
<p>There's exposed water ice on Mars, like <a href="https://i.sstatic.net/lUarh.jpg" rel="noreferrer">in craters like this</a></p>

<p>At the same time, Mars has dust storm, covering the solar panels of rovers, and occasionally <a href="https://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms" rel="noreferrer">covering the entire planet</a></p>

<p>So why is this ice not covered in dust?</p>

<p>I understand that dry carbon dioxide ice can maintain a clean surface, as it's seasonally sublimated into the atmosphere and re-deposited, but how come water ice (at least some of it) is also left clean?</p>

CC BY-SA 4.0
2019-09-22T21:40:15.280Z
Because water ice also sublimates? Water follows a similar seasonal cycle on Mars as $CO_2$. We can for example, follow the water ice ring that forms around the polar caps.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-09-23T18:11:49.160Z
@AtmosphericPrisonEscape  Perhaps you mean " because water also freezes out of the Martian atmosphere" ?
Carl Witthoft
CC BY-SA 4.0
2019-09-24T07:53:26.830Z
who says it isn't, at times? On earth, ice gets covered in dust, and then the wind picks up and the dust gets blown away. No reason to believe the same isn't happening on Mars.
jwenting
CC BY-SA 4.0
2019-09-26T17:00:41.630Z
Frost at the Viking two landing site (1976): http://www.planetary.org/multimedia/space-images/mars/viking2_frost_stryk.html
Wayfaring Stranger
CC BY-SA 4.0
2023-11-06T16:09:31.463Z
Check recently asked in Space SE: https://space.stackexchange.com/questions/64681/why-are-the-martian-poles-not-covered-by-dust. It is essentially same question but there is a good answer.
Nilay Ghosh
<mars>
Why is ice on Mars not covered in dust?
SE - stop firing the good guys
# Why is ice on Mars not covered in dust?

(Asked by: username_0 on 2019-09-22)

There's exposed water ice on Mars, like [in craters like this](https://i.sstatic.net/lUarh.jpg)

At the same time, Mars has dust storm, covering the solar panels of rovers, and occasionally [covering the entire planet](https://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms)

So why is this ice not covered in dust?

I understand that dry carbon dioxide ice can maintain a clean surface, as it's seasonally sublimated into the atmosphere and re-deposited, but how come water ice (at least some of it) is also left clean?

**Tags:** mars
> **Comments:**
> **username_1**: Because water ice also sublimates? Water follows a similar seasonal cycle on Mars as $CO_2$. We can for example, follow the water ice ring that forms around the polar caps.  
> **username_2**: @AtmosphericPrisonEscape  Perhaps you mean " because water also freezes out of the Martian atmosphere" ?  
> **username_3**: who says it isn't, at times? On earth, ice gets covered in dust, and then the wind picks up and the dust gets blown away. No reason to believe the same isn't happening on Mars.  
> **username_4**: Frost at the Viking two landing site (1976): http://www.planetary.org/multimedia/space-images/mars/viking2_frost_stryk.html  
> **username_5**: Check recently asked in Space SE: https://space.stackexchange.com/questions/64681/why-are-the-martian-poles-not-covered-by-dust. It is essentially same question but there is a good answer.  

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## 2 answers

### Answer by username_6 on 2019-09-25. Score: 5

A lot of the water ice on mars is covered with dust. NASA's Phoenix mars lander only had to scrape off some of it to find the layer of ice underneath as seen here: <https://www.nasa.gov/mission_pages/phoenix/images/press/sol_020_024_change_dodo_v3.html>

> **Comments:**
> **username_0**: I'm not implying that **all** ice is clean out in the open, I'm asking why the exposed ice is exposed.  
> **username_6**: The Martian atmosphere is too thin for water to exist in a liquid state so the ice will just freeze directly to a solid and then evaporate back into a gas.  Usually this cycle follows the seasons, and if the ice freezes out in the winter and evaporates in the summer faster than it can get coated in dust, it just stays exposed throughout the Martian winter before evaporating.  
> **username_6**: To add, water ice is following the same seasonal sublimation process you outline in your question for CO2, similarly leaving a clean surface.  

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### Answer by username_7 on 2019-10-05. Score: 3

One hypothesis:

> at first there is a rapid decrease
> in albedo, which is then followed by a rapid increase. The
> decrease could be due to dust contamination after all
> the CO2 frost sublimation; as temperature continues to rise
> up, dust could thermally sink into the water–ice and/or fall
> into cracks between larger grains of water–ice  
> [A conceptual model for explanation of Albedo changes
> in Martian craters](https://pdfs.semanticscholar.org/b05a/165a8047fb4ba9556d682c371b74455dfc57.pdf?_ga=2.5833207.578246397.1570243032-929020594.1570243032), p.889.

Also, the [north polar ice cap is slowly thickening](https://earthsky.org/space/ice-ages-and-ice-at-mars-polar-cap), by 70 microns per year, which might bury the dust.


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