<p>See <a href="https://space.stackexchange.com/a/39090/28871">this answer</a>.</p>
<blockquote>
<p>Actually <a href="https://www.space.com/16235-mars-snowflakes-tiny-snow.html" rel="nofollow noreferrer">already snows on Mars</a>. The snow, made of carbon dioxide, has been observed and studied by orbiting spacecraft. Aside from the different chemical composition from the stuff we shovel on Earth, Martian <span class="math-container">$\text{CO}_2$</span> snow also is very finely divided, microscopic in size in fact; likely this is related to the low density of available material and the very fine nature of the dust on which the snowflakes nucleate. In fact studying the snow could provide clues about the atmospheric Martian dust on which it nucleates.</p>
</blockquote>
<blockquote>
<p>Details are published in the <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JE005040" rel="nofollow noreferrer"><em>Journal of Geophysical Research</em></a>.</p>
</blockquote>
<p>In addition:</p>
<blockquote>
<p>Indirect evidence for water ice snow has also been found. According to an article published in <a href="https://www.nature.com/articles/ngeo3008" rel="nofollow noreferrer"><em>Nature</em></a>, mixing layers have been identified from orbiting spacecraft and water-ice precipitation signatures have been found by the Phoenix lander. Simulations show that such signatures are consistent with snow formation, with the water-ice snow expected to fall at night (as temperatures cool and the atmosphere can retain less water vapor). The arcticle does not claim any direct detection of water-ice snow.&quot;</p>
</blockquote>

CC BY-SA 4.0
2021-03-17T14:29:19.093Z
Done that @uhoh.
Oscar Lanzi
CC BY-SA 4.0
2021-03-17T14:33:08.873Z
looks great, many thanks!
uhoh
CC BY-SA 4.0
2020-12-03T19:48:37.563Z
2021-03-17T00:09:09.923Z
2021-03-17T00:09:09.923Z
Oscar Lanzi
<p>The NASA Goddard science education page answer to <a href="http://teacherlink.ed.usu.edu/tlnasa/reference/imaginedvd/files/imagine/docs/ask_astro/answers/980403c.html" rel="nofollow noreferrer">Reading about Mars, I noticed that it has .03% of water vapor in it's atmosphere, and my question was if it has water vapor why doesn't it have precipitation?</a> says</p>
<blockquote>
<p>Mars does have precipitation.</p>
<p>[...]<strong>However, this precipitation most likely takes the form of frost, rather than rain or snow.</strong> The ground is likely to be colder than the air (especially on cold clear nights), and so air hitting the ground cools and the water freezes to the ground as frost. Viking II (a Mars lander in the 1970's) saw frost on the ground some mornings.</p>
<p>A part of the polar ice caps of Mars is made of precipitated water ice (the rest is made of carbon dioxide as 'dry ice').</p>
</blockquote>
<p>However another educational page <a href="https://www.scholastic.com/teachers/articles/teaching-content/precipitation-weather/" rel="nofollow noreferrer">Precipitation (Weather)</a> says:</p>
<blockquote>
<p>Precipitation in meteorology refers to all forms of liquid or solid water particles that form in the atmosphere and then fall to the earth's surface. Types of precipitation include hail, sleet, snow, rain, and drizzle. <strong>Frost and dew are not classified as precipitation because they form directly on solid surfaces.</strong></p>
</blockquote>
<p>Mars has polar ice caps and a 25.19° inclination similar to that of Earth's. We see the polar caps shrink and grow regularly with the seasons each year.</p>
<p><strong>Questions:</strong></p>
<ol>
<li>Can we say that the changes in the polar ice caps is due to &quot;frost&quot;?</li>
<li>Can we say that the changes in the polar ice caps is due to &quot;precipitation&quot;?</li>
<li>Is there really precipitation on Mars? Does frost count?</li>
</ol>

CC BY-SA 4.0
2020-11-06T20:18:33.970Z
For me, frost is frozen condensation, where atmospheric moisture has directly condensed onto a surface. In effect, frost is frozen dew. I also regard weather related precipitation as something that as fallen from a height. However, chemical precipitation is the formation of a solid (or insoluble) substance from a solution due to a decrease in the solubility of the substance. Thus if atmospheric gases are a solution & solid frost forms at the bottom of the solution maybe frost can be considered to be a precipitate.
Fred
CC BY-SA 4.0
2020-11-07T00:34:52.053Z
@Fred aha! I didn't connect the two usages of the term. Don't precipitates generally form in solution and only fall after they get large enough to sink at a reasonable rate? If they form directly and conformally on to all surfaces (including the sides of the container) I don't think that's called precipitation in Chemistry. But let's find out: [Are precipitation and crystallization the same things in Chemistry and Meteorology?](https://chemistry.stackexchange.com/q/142430/16035)
uhoh
CC BY-SA 4.0
2020-11-07T01:02:54.053Z
I'll be interested to find out what our learned friends over in Chemistry have to say. My other thought is for a drop a water to form in the atmosphere, it does so on an airborne aerosol. As more water condenses on the aerosol a rain drop is formed. If the temperature is cold enough the drop freezes into hail or snow. For frost to form would it also need a nucleus to form onto? Frost I've seen forms on the ground or ground items, such as grass. I've never seen it form on the outside walls or houses. I've seen thick ice form on cars resulting from frozen dew but to me frost seems more delicate.
Fred
CC BY-SA 4.0
2020-11-07T01:07:06.230Z
@Fred You've never had the pleasure of seeing frost-covered windows? http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm or https://community.snapwire.co/photo/detail/5adbdacd582c2e301b8b458f
uhoh
CC BY-SA 4.0
2020-11-07T01:20:29.293Z
Thanks :-) I know cold winters, but not **frozen** ones. Snow can sometimes be a novelty.
Fred
CC BY-SA 4.0
2020-11-07T01:24:12.007Z
@Fred Due to geography I haven't seen this in ages. Food, language, culture, no problem, but oh I miss a cold frosty morning, ice crunching under my feet, the sound of cross-country skis on fresh snow, building snow forts...
uhoh
CC BY-SA 4.0
2020-11-07T01:29:33.933Z
It sounds more inviting than having ones shoes getting stuck to roads when bitumen melts due to seemingly countless days of plus 40 C degree temperatures.
Fred
CC BY-SA 4.0
2020-11-07T21:54:33.613Z
In addition to the technical answer of what is a precipitate, I think there may be a slight technical difference. If you consider the first website, it is called "ask an astrophysicist." An astrophysicist may not draw a distinction between frost and precipitation in the same sense a meteorologist might. Its also worth considering that inaccuracies can form as a result of simplification in communication, especially for the general public.
BarocliniCplusplus
CC BY-SA 4.0
2020-11-07T23:57:49.443Z
@BarocliniCplusplus indeed! That link arose in [a discussion](https://astronomy.stackexchange.com/questions/39588/what-if-a-global-killer-hit-mars#comment79953_39588) about martian weather elsewhere.
uhoh
<precipitation><terminology><mars><water-vapour>
Is there really precipitation on Mars? Does frost count?
uhoh
# Is there really precipitation on Mars? Does frost count?

(Asked by: username_0 on 2020-11-05)

The NASA Goddard science education page answer to [Reading about Mars, I noticed that it has .03% of water vapor in it's atmosphere, and my question was if it has water vapor why doesn't it have precipitation?](http://teacherlink.ed.usu.edu/tlnasa/reference/imaginedvd/files/imagine/docs/ask_astro/answers/980403c.html) says

> Mars does have precipitation.
>
> [...]**However, this precipitation most likely takes the form of frost, rather than rain or snow.** The ground is likely to be colder than the air (especially on cold clear nights), and so air hitting the ground cools and the water freezes to the ground as frost. Viking II (a Mars lander in the 1970's) saw frost on the ground some mornings.
>
> A part of the polar ice caps of Mars is made of precipitated water ice (the rest is made of carbon dioxide as 'dry ice').

However another educational page [Precipitation (Weather)](https://www.scholastic.com/teachers/articles/teaching-content/precipitation-weather/) says:

> Precipitation in meteorology refers to all forms of liquid or solid water particles that form in the atmosphere and then fall to the earth's surface. Types of precipitation include hail, sleet, snow, rain, and drizzle. **Frost and dew are not classified as precipitation because they form directly on solid surfaces.**

Mars has polar ice caps and a 25.19° inclination similar to that of Earth's. We see the polar caps shrink and grow regularly with the seasons each year.

**Questions:**

1. Can we say that the changes in the polar ice caps is due to "frost"?
2. Can we say that the changes in the polar ice caps is due to "precipitation"?
3. Is there really precipitation on Mars? Does frost count?

**Tags:** precipitation, terminology, mars, water-vapour

> **Comments:**
> **username_1**: For me, frost is frozen condensation, where atmospheric moisture has directly condensed onto a surface. In effect, frost is frozen dew. I also regard weather related precipitation as something that as fallen from a height. However, chemical precipitation is the formation of a solid (or insoluble) substance from a solution due to a decrease in the solubility of the substance. Thus if atmospheric gases are a solution & solid frost forms at the bottom of the solution maybe frost can be considered to be a precipitate.  
> **username_0**: @username_1 aha! I didn't connect the two usages of the term. Don't precipitates generally form in solution and only fall after they get large enough to sink at a reasonable rate? If they form directly and conformally on to all surfaces (including the sides of the container) I don't think that's called precipitation in Chemistry. But let's find out: [Are precipitation and crystallization the same things in Chemistry and Meteorology?](https://chemistry.stackexchange.com/q/142430/16035)  
> **username_1**: I'll be interested to find out what our learned friends over in Chemistry have to say. My other thought is for a drop a water to form in the atmosphere, it does so on an airborne aerosol. As more water condenses on the aerosol a rain drop is formed. If the temperature is cold enough the drop freezes into hail or snow. For frost to form would it also need a nucleus to form onto? Frost I've seen forms on the ground or ground items, such as grass. I've never seen it form on the outside walls or houses. I've seen thick ice form on cars resulting from frozen dew but to me frost seems more delicate.  
> **username_0**: @username_1 You've never had the pleasure of seeing frost-covered windows? http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm or https://community.snapwire.co/photo/detail/5adbdacd582c2e301b8b458f  
> **username_1**: Thanks :-) I know cold winters, but not **frozen** ones. Snow can sometimes be a novelty.  
> **username_0**: @username_1 Due to geography I haven't seen this in ages. Food, language, culture, no problem, but oh I miss a cold frosty morning, ice crunching under my feet, the sound of cross-country skis on fresh snow, building snow forts...  
> **username_1**: It sounds more inviting than having ones shoes getting stuck to roads when bitumen melts due to seemingly countless days of plus 40 C degree temperatures.  
> **username_2**: In addition to the technical answer of what is a precipitate, I think there may be a slight technical difference. If you consider the first website, it is called "ask an astrophysicist." An astrophysicist may not draw a distinction between frost and precipitation in the same sense a meteorologist might. Its also worth considering that inaccuracies can form as a result of simplification in communication, especially for the general public.  
> **username_0**: @username_2 indeed! That link arose in [a discussion](https://astronomy.stackexchange.com/questions/39588/what-if-a-global-killer-hit-mars#comment79953_39588) about martian weather elsewhere.  

---

## 1 answers

### Answer by username_3 on 2020-12-03. Score: 2 | Accepted answer

See [this answer](https://space.stackexchange.com/a/39090/28871).

> Actually [already snows on Mars](https://www.space.com/16235-mars-snowflakes-tiny-snow.html). The snow, made of carbon dioxide, has been observed and studied by orbiting spacecraft. Aside from the different chemical composition from the stuff we shovel on Earth, Martian $\text{CO}\_2$ snow also is very finely divided, microscopic in size in fact; likely this is related to the low density of available material and the very fine nature of the dust on which the snowflakes nucleate. In fact studying the snow could provide clues about the atmospheric Martian dust on which it nucleates.

> Details are published in the [*Journal of Geophysical Research*](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JE005040).

In addition:

> Indirect evidence for water ice snow has also been found. According to an article published in [*Nature*](https://www.nature.com/articles/ngeo3008), mixing layers have been identified from orbiting spacecraft and water-ice precipitation signatures have been found by the Phoenix lander. Simulations show that such signatures are consistent with snow formation, with the water-ice snow expected to fall at night (as temperatures cool and the atmosphere can retain less water vapor). The arcticle does not claim any direct detection of water-ice snow."

> **Comments:**
> **username_3**: Done that @username_0.  
> **username_0**: looks great, many thanks!  

---

