<p>This <a href="https://earthscience.stackexchange.com/a/21109/6031">answer to <em>Would a gold-containing meteor cause it to “rain” gold?</em></a> says (in part):</p>
<blockquote>
<p>Meteors, when in space, are very very <strong>very <em>very</em></strong> cold. Their travel duration in Earth's atmosphere is very short, just a couple of seconds. Actual melting only occurs at the very most outer layer of the meteorite. This is not sufficient to heat up the interior of the meteorite to any significant degree. In fact, some meteorite falls have found to have frost on them when found soon after landing, because they condense the moisture in the air around them!</p>
</blockquote>
<p>The &quot;very very <strong>very <em>very</em></strong>&quot; might be overstated, but let's see if they could be below the freezing point of water.</p>
<p>The <a href="https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature" rel="nofollow noreferrer">surface temperature of an asteroid</a> can be applied to roughly spherical objects of arbitrary size, there's no scale in the derivation; it should work for centimeter-sized objects as well as it would for a planet sized rocky object <em>sans atmosphere</em>.</p>
<p><span class="math-container">$$T^4 = \frac{L_0 (1-A)}{\epsilon \sigma 16 \pi a^2 }$$</span></p>
<p>Here <span class="math-container">$L_0$</span> is the total <a href="https://en.wikipedia.org/wiki/Solar_luminosity" rel="nofollow noreferrer">solar luminosity</a> of 3.827×10<sup>26</sup> W and <span class="math-container">$\sigma$</span> is the <a href="https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_constant" rel="nofollow noreferrer">Stefan-Boltsman constant</a> 5.67×10<sup>-8</sup> W/m<sup>2</sup>/K<sup>4</sup>. <span class="math-container">$a$</span> is the distance from the Sun, let's assume that the meteor has been near 1 AU long enough (weeks) to reach equilibrium temperature. <span class="math-container">$\epsilon$</span> is the asteroid's infra-red emissivity and a value of 0.9 is given as typical.</p>
<p>The ~visible light average albedo <span class="math-container">$A$</span> of asteroids is the big variable here. They are usually pretty dark but there is a lot of variation and measurements are often based on other assumptions. I'll calculate the equilibrium temperature for a few, but as one can guess 1 minus a small number is close to 1, and after you take the fourth root, it's very close to 1!</p>
<pre><code>Albedo    Temperature
(vis)       K     C
 0.05     282     8
 0.10     278     5
 0.2      270    -3
 0.5      240    -33
</code></pre>
<p>So for a meteor to be <em>even barely below</em> the freezing point of water it would have to have an <em>above-average albedo</em>.</p>
<p>It seems to me that after <a href="https://astronomy.stackexchange.com/a/38912/7982">tens of seconds to minutes</a> there is not enough time for the transient heat pulse on the skin to do more than melt the surface, but the radiative heating from the plasma created for larger meteors can be quite intense, so they sometimes &quot;explode&quot; or breakup due to stress.</p>
<p>Nonetheless the core temperatures of larger meteorites reaching the surface could very well reflect the temperature in space.</p>
<p>So a meteorite becoming &quot;frosty&quot; soon after landing is plausible if it were of a higher than average albedo.</p>
<p><strong>Question:</strong> Have &quot;frosty meteorites&quot; ever been observed soon after landing? Are there photos?</p>
<hr />
<p>Related:</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/38909/7982">How long between the moment a meteor is first visible and the moment a meteorite hits the ground?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/23615/7982">How much time does it take for a meteor (shooting star) to touch the ground after its combustion?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/35984/7982">How complicated is the heating of meteors?</a></li>
<li><a href="https://earthscience.stackexchange.com/q/127/6031">What temperature do small meteorites have on impact</a> there are answers posted but no temperatures... <em>yet!</em></li>
<li><a href="https://earthscience.stackexchange.com/q/14864/6031">Is it possible to estimate the size of a meteorite from its remains?</a></li>
</ul>
<hr />
<p><a href="https://i.sstatic.net/42qhl.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/42qhl.png" alt="Asteroid albedos: graphs of data by Wm. Robert Johnston last updated 25 March 2017" /></a></p>
<p><strong>above:</strong> From <a href="http://www.johnstonsarchive.net/astro/astalbedo.html" rel="nofollow noreferrer">Asteroid albedos: graphs of data by Wm. Robert Johnston last updated 25 March 2017</a> <strong>below:</strong> From NYTimes' <a href="https://www.nytimes.com/2021/04/29/science/meteorite-botswana-asteroid.html" rel="nofollow noreferrer">A 22-Million-Year Journey From the Asteroid Belt to Botswana</a> &quot;A fragment of the asteroid 2018 LA, found in the Central Kalahari Game Reserve in Botswana in 2018.Credit...P. Jenniskens/SETI Institute&quot;</p>
<p>This is what got me thinking about this topic</p>
<p><a href="https://i.sstatic.net/cUWcZ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cUWcZ.png" alt="A fragment of the asteroid 2018 LA, found in the Central Kalahari Game Reserve in Botswana in 2018.Credit...P. Jenniskens/SETI Institute" /></a></p>
<p><strong>For comparison:</strong> from <a href="https://space.stackexchange.com/a/24660/12102">this answer to <em>Who discovered “Egg Rock”? The Curiosity rover or people?</em></a></p>
<blockquote>
<p>...Cropped section of image of &quot;Egg Rock&quot; from <a href="http://redplanet.asu.edu/?p=21047" rel="nofollow noreferrer">redplanet.asu.edu/?p=21047</a> showing the spots where Curiosity's ChemCam laser has ablated material.</p>
<p><a href="https://i.sstatic.net/KJ2nK.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/KJ2nK.jpg" alt="Egg rock on Mars showing the spots where Curiosity's ChemCam laser has ablated material." /></a></p>
</blockquote>
<p>Spoiler alert:</p>
<blockquote class="spoiler">
<p> <strong>People did!</strong></p>
</blockquote>

CC BY-SA 4.0
2021-04-30T10:26:11.113Z
Have you read [this](http://curious.astro.cornell.edu/about-us/75-our-solar-system/comets-meteors-and-asteroids/meteorites/314-are-meteorites-hot-or-cold-when-they-hit-earth-intermediate)?
Gimelist
CC BY-SA 4.0
2021-04-30T10:47:03.800Z
@Gimelist have now! :-)
uhoh
CC BY-SA 4.0
2021-04-30T11:01:58.050Z
Something that would be required for a frosty or wet meteorite would be for the atmosphere at the landing site to be have a high humidity & for the dew point conditions to be satisfied. Any dew or frost that would form on the meteorite would be derived from the moisture in the atmosphere.
Fred
CC BY-SA 4.0
2021-04-30T11:07:37.897Z
@Fred I bought my friend [a dry/wet bulb thermometer](https://earthscience.stackexchange.com/q/19151) for fun and science, but it's pretty boring because here the humidity is always high and the two never differ much. (we were both disappointed) Here it seems that anything below 0 C frosts up instantly, so I assumed that any water at all in the atmosphere would be sufficient, but I guess that's not true? At say 20 C there's some nonzero relative humidity where a -3 C surface would not accumulate any frost (given no wind, no sunshine, etc...)?
uhoh
CC BY-SA 4.0
2021-04-30T11:24:48.663Z
[Whirling hygrometers](https://www.preservationequipment.com/Catalogue/Instruments/Hygrometers/Whirling-Hygrometer) are a lot more fun. They have to be rotated to function properly - if only for 30 to 60 seconds. ;-)
Fred
CC BY-SA 4.0
2021-04-30T12:44:01.333Z
@Fred Oh that looks really familliar; I think I've seen one used, perhaps in a movie... **update:** I've just asked [How does a whirling hygrometer work, how does it differ from static dry/wet bulb thermometer, and how to obtain humidity from its readings?](https://earthscience.stackexchange.com/q/21198/6031)
uhoh
<atmosphere><meteorite>
Have "frosty meteorites" ever been observed soon after landing? Are there photos?
uhoh
# Have "frosty meteorites" ever been observed soon after landing? Are there photos?

(Asked by: username_0 on 2021-04-30)

This [answer to *Would a gold-containing meteor cause it to “rain” gold?*](https://earthscience.stackexchange.com/a/21109/6031) says (in part):

> Meteors, when in space, are very very **very *very*** cold. Their travel duration in Earth's atmosphere is very short, just a couple of seconds. Actual melting only occurs at the very most outer layer of the meteorite. This is not sufficient to heat up the interior of the meteorite to any significant degree. In fact, some meteorite falls have found to have frost on them when found soon after landing, because they condense the moisture in the air around them!

The "very very **very *very***" might be overstated, but let's see if they could be below the freezing point of water.

The [surface temperature of an asteroid](https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature) can be applied to roughly spherical objects of arbitrary size, there's no scale in the derivation; it should work for centimeter-sized objects as well as it would for a planet sized rocky object *sans atmosphere*.

$$T^4 = \frac{L\_0 (1-A)}{\epsilon \sigma 16 \pi a^2 }$$

Here $L\_0$ is the total [solar luminosity](https://en.wikipedia.org/wiki/Solar_luminosity) of 3.827×1026 W and $\sigma$ is the [Stefan-Boltsman constant](https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_constant) 5.67×10-8 W/m2/K4. $a$ is the distance from the Sun, let's assume that the meteor has been near 1 AU long enough (weeks) to reach equilibrium temperature. $\epsilon$ is the asteroid's infra-red emissivity and a value of 0.9 is given as typical.

The ~visible light average albedo $A$ of asteroids is the big variable here. They are usually pretty dark but there is a lot of variation and measurements are often based on other assumptions. I'll calculate the equilibrium temperature for a few, but as one can guess 1 minus a small number is close to 1, and after you take the fourth root, it's very close to 1!

```
Albedo    Temperature
(vis)       K     C
 0.05     282     8
 0.10     278     5
 0.2      270    -3
 0.5      240    -33

```

So for a meteor to be *even barely below* the freezing point of water it would have to have an *above-average albedo*.

It seems to me that after [tens of seconds to minutes](https://astronomy.stackexchange.com/a/38912/7982) there is not enough time for the transient heat pulse on the skin to do more than melt the surface, but the radiative heating from the plasma created for larger meteors can be quite intense, so they sometimes "explode" or breakup due to stress.

Nonetheless the core temperatures of larger meteorites reaching the surface could very well reflect the temperature in space.

So a meteorite becoming "frosty" soon after landing is plausible if it were of a higher than average albedo.

**Question:** Have "frosty meteorites" ever been observed soon after landing? Are there photos?

---

Related:

* [How long between the moment a meteor is first visible and the moment a meteorite hits the ground?](https://astronomy.stackexchange.com/q/38909/7982)
* [How much time does it take for a meteor (shooting star) to touch the ground after its combustion?](https://astronomy.stackexchange.com/q/23615/7982)
* [How complicated is the heating of meteors?](https://astronomy.stackexchange.com/q/35984/7982)
* [What temperature do small meteorites have on impact](https://earthscience.stackexchange.com/q/127/6031) there are answers posted but no temperatures... *yet!*
* [Is it possible to estimate the size of a meteorite from its remains?](https://earthscience.stackexchange.com/q/14864/6031)

---

[![Asteroid albedos: graphs of data by Wm. Robert Johnston last updated 25 March 2017](https://i.sstatic.net/42qhl.png)](https://i.sstatic.net/42qhl.png)

**above:** From [Asteroid albedos: graphs of data by Wm. Robert Johnston last updated 25 March 2017](http://www.johnstonsarchive.net/astro/astalbedo.html) **below:** From NYTimes' [A 22-Million-Year Journey From the Asteroid Belt to Botswana](https://www.nytimes.com/2021/04/29/science/meteorite-botswana-asteroid.html) "A fragment of the asteroid 2018 LA, found in the Central Kalahari Game Reserve in Botswana in 2018.Credit...P. Jenniskens/SETI Institute"

This is what got me thinking about this topic

[![A fragment of the asteroid 2018 LA, found in the Central Kalahari Game Reserve in Botswana in 2018.Credit...P. Jenniskens/SETI Institute](https://i.sstatic.net/cUWcZ.png)](https://i.sstatic.net/cUWcZ.png)

**For comparison:** from [this answer to *Who discovered “Egg Rock”? The Curiosity rover or people?*](https://space.stackexchange.com/a/24660/12102)

> ...Cropped section of image of "Egg Rock" from [redplanet.asu.edu/?p=21047](http://redplanet.asu.edu/?p=21047) showing the spots where Curiosity's ChemCam laser has ablated material.
>
> [![Egg rock on Mars showing the spots where Curiosity's ChemCam laser has ablated material.](https://i.sstatic.net/KJ2nK.jpg)](https://i.sstatic.net/KJ2nK.jpg)

Spoiler alert:

> **People did!**

**Tags:** atmosphere, meteorite

> **Comments:**
> **username_1**: Have you read [this](http://curious.astro.cornell.edu/about-us/75-our-solar-system/comets-meteors-and-asteroids/meteorites/314-are-meteorites-hot-or-cold-when-they-hit-earth-intermediate)?  
> **username_0**: @username_1 have now! :-)  
> **username_2**: Something that would be required for a frosty or wet meteorite would be for the atmosphere at the landing site to be have a high humidity & for the dew point conditions to be satisfied. Any dew or frost that would form on the meteorite would be derived from the moisture in the atmosphere.  
> **username_0**: @username_2 I bought my friend [a dry/wet bulb thermometer](https://earthscience.stackexchange.com/q/19151) for fun and science, but it's pretty boring because here the humidity is always high and the two never differ much. (we were both disappointed) Here it seems that anything below 0 C frosts up instantly, so I assumed that any water at all in the atmosphere would be sufficient, but I guess that's not true? At say 20 C there's some nonzero relative humidity where a -3 C surface would not accumulate any frost (given no wind, no sunshine, etc...)?  
> **username_2**: [Whirling hygrometers](https://www.preservationequipment.com/Catalogue/Instruments/Hygrometers/Whirling-Hygrometer) are a lot more fun. They have to be rotated to function properly - if only for 30 to 60 seconds. ;-)  
> **username_0**: @username_2 Oh that looks really familliar; I think I've seen one used, perhaps in a movie... **update:** I've just asked [How does a whirling hygrometer work, how does it differ from static dry/wet bulb thermometer, and how to obtain humidity from its readings?](https://earthscience.stackexchange.com/q/21198/6031)  

---

## 0 answers

