<p>Four locations in which &quot;snow&quot; might be falling.</p>
<p>The most Earth-like moon might be Titan. It is large enough to have a substantial atmosphere and there seems to be an &quot;ethane cycle&quot; that mimics the water cycle on Earth.  It is likely that there is ethane snow near the polar regions of Titan. This is mentioned on the Wikipedia page on the <a href="https://en.wikipedia.org/wiki/Climate_of_Titan#:%7E:text=One%20hypothesis%20is%20that%20it%20is%20currently%20raining%20(or%2C%20if%20cool%20enough%2C%20snowing)%20on%20the%20north%20pole%3B" rel="nofollow noreferrer">climate of Titan</a></p>
<p>Io is not Earth-like at all, but it does have so many volcanos that spew hot sulphur vapour into the sky.  This sulphur sublime to sulphur crystals that fall to the ground as &quot;snow&quot;.  However, with no atmosphere to speak of, the crystals will be falling ballistically, and even though surface gravity is weak, the'll be moving pretty fast when they reach the ground. See this <a href="https://science.nasa.gov/science-news/science-at-nasa/2001/ast16oct_1#:%7E:text=Snow%20on%20Io%20is%20made,thin%20atmosphere%20is%20space%2Dcold." rel="nofollow noreferrer">article in Nasa science</a></p>
<p>There are cirrus clouds in the atmosphere of Neptune. And just as if you were to go into a cirrus cloud on Earth, you would find that they were full of crystals (of ice on Earth, but Methane on Neptune).  And like on Earth, they would be falling down.  On Earth, the ice in cirrus clouds turns back into water vapour long before it reaches the surface (so these don't fit your criteria).  On Neptune, there is no surface, so the &quot;reach the surface&quot; aspect is moot. You might call these &quot;snow&quot;, if you were in a hot air ballon and floating along with them.</p>
<p>There is speculation about carbon precipitation in the form of diamond in the lower atmospheres of some of the giant planets - leading to romantic headlines about &quot;snowing diamonds on Jupiter.&quot;</p>

CC BY-SA 4.0
2023-02-16T09:24:07.467Z
2023-02-16T09:24:07.467Z
James K
<p>It most certainly snows on Mars. As described on <a href="https://space.stackexchange.com/questions/39089/would-snow-fall-on-the-surface-of-mars-because-of-uncovering-the-ice-deposit-in#39090">this Earth Science SE answer</a>, evidence exists for both water and carbon dioxide snowfall on that planet, with carbon dioxide presumably more prominent given the composition of the Martian atmosphere.</p>

CC BY-SA 4.0
2023-02-16T01:15:00.027Z
2023-02-16T01:15:00.027Z
Oscar Lanzi
<p><strong>What do we know about extraterrestrial <a href="https://en.m.wikipedia.org/wiki/Snow" rel="nofollow noreferrer">snow</a>?</strong> On which (exo)planets or (exo)moons do we have direct hints for its existance? This is indeed a children's question, but I struggle to answer it conclusively.</p>
<p>I only know about <a href="https://www.nature.com/articles/d41586-017-02650-y#:%7E:text=Mars%20has%20surprisingly%20powerful%20snowstorms,ice%20crystals%20can%20still%20develop." rel="nofollow noreferrer">snow on Mars</a>, <a href="https://en.wikipedia.org/wiki/Venus_snow" rel="nofollow noreferrer">Venus snow</a> (which strictly speaking might be a <a href="https://en.wikipedia.org/wiki/Misnomer" rel="nofollow noreferrer">misnomer</a>) and snow on Titan.</p>
<p>For exoplanets in the habitable zone, the phase diagram of water may of course allow snow if water existed on an exoplanet. What about non-water snow? Which chemical substances which allow snow have been observed so far on other (exo)planets?</p>
<h3>Generalized definition of snow</h3>
<p>As <strong>snow</strong> I would define as <strong>precipitation of any (chemical) kind which is not in liquid or gaseous state</strong>. The solid objects (most likely crystals) should be moving downward in from the sky and is possibly reaching the ground (if there is any).</p>
<p>This definition excludes ground frost and hail. Hail is excluded since these layered balls of (water ice and/or other solids) are actually moving repeatedly and significantly moving upward (on Earth in <a href="https://en.wikipedia.org/wiki/Cumulonimbus_cloud" rel="nofollow noreferrer">Comulonimbus clouds</a>). The definition <em>does</em> include solid clear sky precipitation aka <a href="https://en.wikipedia.org/wiki/Diamond_dust" rel="nofollow noreferrer">diamond dust</a>.</p>

CC BY-SA 4.0
2021-01-17T16:06:24.323Z
Don't know if it counts but there is water ice on Europa
jng224
CC BY-SA 4.0
2021-01-17T21:06:00.263Z
The closest I could find is this article: https://www.cnet.com/news/nasa-europa-jupiter-moon-hubble-ocean-life-water-plumes/ (though not a publication). I assume the moon's atmosphere is too tenuous for actual clouds to form.
jng224
CC BY-SA 4.0
2021-01-17T21:51:49.253Z
related in Earth science SE [Is there really precipitation on Mars? Does frost count?](https://earthscience.stackexchange.com/q/20440/6031) and [this answer](https://space.stackexchange.com/a/39090/12102) in Space SE. Slightly related and background information here in Astronomy SE: [Why are only the poles of Mars frozen, despite too cold temperatures on lower latitudes?](https://astronomy.stackexchange.com/q/39690/7982)
uhoh
CC BY-SA 4.0
2021-01-17T23:49:19.113Z
I heard that frozen nitrogen snows on Pluto...
WarpPrime
CC BY-SA 4.0
2021-01-18T16:32:06.290Z
Don't forget the Polycyclic Aromatic Hydrocarbon snow on Titan!  http://spaceref.com/saturn/cassini-sees-precursors-to-aerosol-snow-on-titan.html  Maybe there will be enough comments to put together a good answer soon!
Connor Garcia
CC BY-SA 4.0
2021-01-19T00:42:03.240Z
Co2 snow on mars and titan... https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.space.com/amp/17583-mars-snow-carbon-dioxide-discovery.html&ved=2ahUKEwj4i52936buAhWBxYUKHZtaAd4QFjACegQILBAB&usg=AOvVaw3nDB0aCRxcbIkTheZEe7X7&ampcf=1 acetone https://youtu.be/nmktRTHL1NA water ice has 60 degree crystals and snowflakes should be possible with any degrees of branching. A snowflake simulator can be modded for 30 72 90 120 degrees.
bandybabboon
CC BY-SA 4.0
2023-02-16T12:26:49.667Z
I think the Enceladus geysers may provide a kind of snowfall. I have seen models for hot exoplanets with things like iron, silicate, and oxide snow, although I don't think they have been observationally confirmed.
Anders Sandberg
<exoplanet><mars><planetary-atmosphere><venus><titan>
Extraterrestrial snow?
B--rian
# Extraterrestrial snow?

(Asked by: username_0 on 2021-01-17)

**What do we know about extraterrestrial [snow](https://en.m.wikipedia.org/wiki/Snow)?** On which (exo)planets or (exo)moons do we have direct hints for its existance? This is indeed a children's question, but I struggle to answer it conclusively.

I only know about [snow on Mars](https://www.nature.com/articles/d41586-017-02650-y#:%7E:text=Mars%20has%20surprisingly%20powerful%20snowstorms,ice%20crystals%20can%20still%20develop.), [Venus snow](https://en.wikipedia.org/wiki/Venus_snow) (which strictly speaking might be a [misnomer](https://en.wikipedia.org/wiki/Misnomer)) and snow on Titan.

For exoplanets in the habitable zone, the phase diagram of water may of course allow snow if water existed on an exoplanet. What about non-water snow? Which chemical substances which allow snow have been observed so far on other (exo)planets?

### Generalized definition of snow

As **snow** I would define as **precipitation of any (chemical) kind which is not in liquid or gaseous state**. The solid objects (most likely crystals) should be moving downward in from the sky and is possibly reaching the ground (if there is any).

This definition excludes ground frost and hail. Hail is excluded since these layered balls of (water ice and/or other solids) are actually moving repeatedly and significantly moving upward (on Earth in [Comulonimbus clouds](https://en.wikipedia.org/wiki/Cumulonimbus_cloud)). The definition *does* include solid clear sky precipitation aka [diamond dust](https://en.wikipedia.org/wiki/Diamond_dust).

**Tags:** exoplanet, mars, planetary-atmosphere, venus, titan
> **Comments:**
> **username_1**: Don't know if it counts but there is water ice on Europa  
> **username_1**: The closest I could find is this article: https://www.cnet.com/news/nasa-europa-jupiter-moon-hubble-ocean-life-water-plumes/ (though not a publication). I assume the moon's atmosphere is too tenuous for actual clouds to form.  
> **username_2**: related in Earth science SE [Is there really precipitation on Mars? Does frost count?](https://earthscience.stackexchange.com/q/20440/6031) and [this answer](https://space.stackexchange.com/a/39090/12102) in Space SE. Slightly related and background information here in Astronomy SE: [Why are only the poles of Mars frozen, despite too cold temperatures on lower latitudes?](https://astronomy.stackexchange.com/q/39690/7982)  
> **username_3**: I heard that frozen nitrogen snows on Pluto...  
> **username_4**: Don't forget the Polycyclic Aromatic Hydrocarbon snow on Titan!  http://spaceref.com/saturn/cassini-sees-precursors-to-aerosol-snow-on-titan.html  Maybe there will be enough comments to put together a good answer soon!  
> **username_5**: Co2 snow on mars and titan... https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.space.com/amp/17583-mars-snow-carbon-dioxide-discovery.html&ved=2ahUKEwj4i52936buAhWBxYUKHZtaAd4QFjACegQILBAB&usg=AOvVaw3nDB0aCRxcbIkTheZEe7X7&ampcf=1 acetone https://youtu.be/nmktRTHL1NA water ice has 60 degree crystals and snowflakes should be possible with any degrees of branching. A snowflake simulator can be modded for 30 72 90 120 degrees.  
> **username_6**: I think the Enceladus geysers may provide a kind of snowfall. I have seen models for hot exoplanets with things like iron, silicate, and oxide snow, although I don't think they have been observationally confirmed.  

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## 2 answers

### Answer by username_7 on 2023-02-16. Score: 3 | Accepted answer

Four locations in which "snow" might be falling.

The most Earth-like moon might be Titan. It is large enough to have a substantial atmosphere and there seems to be an "ethane cycle" that mimics the water cycle on Earth. It is likely that there is ethane snow near the polar regions of Titan. This is mentioned on the Wikipedia page on the [climate of Titan](https://en.wikipedia.org/wiki/Climate_of_Titan#:%7E:text=One%20hypothesis%20is%20that%20it%20is%20currently%20raining%20(or%2C%20if%20cool%20enough%2C%20snowing)%20on%20the%20north%20pole%3B)

Io is not Earth-like at all, but it does have so many volcanos that spew hot sulphur vapour into the sky. This sulphur sublime to sulphur crystals that fall to the ground as "snow". However, with no atmosphere to speak of, the crystals will be falling ballistically, and even though surface gravity is weak, the'll be moving pretty fast when they reach the ground. See this [article in Nasa science](https://science.nasa.gov/science-news/science-at-nasa/2001/ast16oct_1#:%7E:text=Snow%20on%20Io%20is%20made,thin%20atmosphere%20is%20space%2Dcold.)

There are cirrus clouds in the atmosphere of Neptune. And just as if you were to go into a cirrus cloud on Earth, you would find that they were full of crystals (of ice on Earth, but Methane on Neptune). And like on Earth, they would be falling down. On Earth, the ice in cirrus clouds turns back into water vapour long before it reaches the surface (so these don't fit your criteria). On Neptune, there is no surface, so the "reach the surface" aspect is moot. You might call these "snow", if you were in a hot air ballon and floating along with them.

There is speculation about carbon precipitation in the form of diamond in the lower atmospheres of some of the giant planets - leading to romantic headlines about "snowing diamonds on Jupiter."


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### Answer by username_8 on 2023-02-16. Score: 2

It most certainly snows on Mars. As described on [this Earth Science SE answer](https://space.stackexchange.com/questions/39089/would-snow-fall-on-the-surface-of-mars-because-of-uncovering-the-ice-deposit-in#39090), evidence exists for both water and carbon dioxide snowfall on that planet, with carbon dioxide presumably more prominent given the composition of the Martian atmosphere.


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