<p>Looking at it with minimal prior knowledge, I think you expect that behaviour if you are on a surface that is sunlit (or recently sunlit) on a body that has no atmosphere.</p>
<p>The very top surface is hot because it absorbs sunlight. It can achieve an equilibrium temperature by radiating this heat back into space or conducting it below the surface.
Since there is no atmosphere, then cooling via convection (as would happen on the Earth is not an option).</p>
<p>If the thermal conductivity is low and the top surface receives of order 1 kW/m<span class="math-container">$^2$</span> (assuming a low albedo), then the surface radiates at a temperature given by
<span class="math-container">$$\sigma T^4 \simeq 1000\ ,$$</span>,
where <span class="math-container">$\sigma$</span> is the Stefan-Boltzmann constant equal to <span class="math-container">$5.7\times 10^{-8}$</span> in SI units. This would give <span class="math-container">$T=364$</span> K (91C), which will be an upper limit because some light is reflected and since Chandrayaan-3 is at the lunar south pole, the sunlight comes in at an angle that probably reduces the flux from my estimate.</p>
<p>If the thermal conductivity is low, and there is no atmosphere or other fluid to transfer the heat downwards, then the temperature will drop rapidly with depth until it reaches the equilibrium temperature of the Moon as a whole. This will be a rough baseline temperature that could be estimated by assuming the Moon as a whole must on average radiate all the sunlight absorbed. Again, ignoring albedo,
<span class="math-container">$$4\pi R^2 \sigma T^4 = 1200 \pi R^2\ ,$$</span>
where <span class="math-container">$R$</span> is the lunar radius (which cancels) and 1200 W/m<span class="math-container">$^2$</span> is the flux of sunlight incident normally on an object at the distance of the Moon from the Sun, with roughly 10% reflected back into space (the lunar albedo). This gives <span class="math-container">$T\simeq 269$</span> K (-4C). This is probably an overestimate if heat transport within the Moon is ineffective, since the lunar south pole will receive less than its fair share of this flux.</p>
<p>Thus I would expect to see a sunlit temperature profile as in the picture, with a high temperature at the surface reducing to minus a few Celsius at depth, but for that trend to reverse when the surface is not illuminated. i.e. For the surface to be well below zero Celsius and colder than the interior, which will remain at minus a few Celsius. That is because the surface can radiate more efficiently than heat can be brought to the surface by thermal conduction.</p>
<p>The surface gradients on Earth will generally not be as sharp because Earth has an atmosphere and other fluids that are able to transport heat much more effectively over these short distances and to cool the surface. The equilibrium temperature of the Earth (i.e. the baseline temperature) is also higher than the Moon because of its atmosphere. I would guess that the closest you would get to lunar conditions would be in a desert, where it is very dry.</p>

CC BY-SA 4.0
2023-08-28T08:45:13.120Z
2023-08-28T11:17:31.103Z
2023-08-28T11:17:31.103Z
ProfRob
<p><a href="https://www.isro.gov.in/Chandrayaan3.html" rel="nofollow noreferrer">ISRO Chandrayaan 3</a> <a href="https://www.msn.com/en-in/news/techandscience/chandrayaan-3-chaste-payload-aboard-vikram-lander-measures-lunar-surface-temperature-how-it-works/ar-AA1fQey6" rel="nofollow noreferrer">released</a> the following data today about the temperature characteristics of lunar soil.</p>
<p><a href="https://i.sstatic.net/JyxKx.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JyxKx.jpg" alt="enter image description here" /></a></p>
<ol>
<li>What secondary and tertiary conclusions can be drawn it?</li>
<li>More specifically, what may be the possible reasons for the rapid drop in temperature from 55 C to -10 C in just 8 cm?</li>
</ol>
<p><em>Clarification: I do not claim it to be correct usage but here is what I meant: Primary conclusions are those that are directly visible from the data. Secondary conclusions build on the primary ones, and so on.</em></p>

CC BY-SA 4.0
2023-08-27T16:48:04.500Z
That the material is not very conductive and the surface is exposed to the Sun?
ProfRob
CC BY-SA 4.0
2023-08-27T19:12:33.193Z
I'm familiar with the notion of "secondary and tertiary" sources.  I'm not familiar with the notion of secondary and tertiary conclusions.  Perhaps I'm the only one here who doesn't know what you mean by this, but could you explain?
James K
CC BY-SA 4.0
2023-08-27T23:31:05.727Z
potentially helpful [this answer to *Do we know the fluctuations and constant temperature depth of the moon?*](https://astronomy.stackexchange.com/a/30532/7982) The area is obviously sunlit at the moment so the top half meter (plus/minus) of loose regolith will be warmer than below. Once it becomes night, that line will look totally different; the bottom will move *a little* to the left (colder) but the top will drop way way down in temperature. This exercise determines the thermal conductivity of this layer. Since a mission to the pole is all about temperature, it's potentially useful info.
uhoh
CC BY-SA 4.0
2023-08-28T10:35:23.443Z
@JamesK I do not claim it to be correct usage but here is what I meant: Primary conclusions are those that are directly visible from the data. Secondary conclusions build on the primary ones, and so on. As an example, ProfRob's comment can be called primary, any specific conclusions about the composition can be called secondary, futher conclusions about the origin and creation history can be called tertiary. (Added this clarification to the question.)
Ritesh Singh
CC BY-SA 4.0
2023-08-28T10:43:29.770Z
@uhoh Thank you, as always! But why is the temperature gradient on Earth not so sharp? Added this to the question as well.
Ritesh Singh
CC BY-SA 4.0
2023-08-28T11:05:14.160Z
Can you add a comparable temperature profile for the Earth if you are to include a further question?
ProfRob
CC BY-SA 4.0
2023-08-28T12:04:51.343Z
@ProfRob Ok sir, I am removing the additional question and accepting your answer since it is complete for the previous question. I will find a similar profile for Earth and ask a separate question.
Ritesh Singh
CC BY-SA 4.0
2023-08-28T12:29:23.077Z
@RiteshSingh *Great (new) question!* For dry sand in the desert you really may see a similar phenomenon, but not nearly as extreme for several reasons. Here's a few: 1) day/night cycles are 27 times faster, 2) the Earth's atmosphere cools the hot sand and warms the cold sand (it's not exposed to the "cold vacuum" of space directly 3) air between the grains can conduct heat (not just the point-to-point sand grain contact) and any water vapor will conduct even more.
uhoh
CC BY-SA 4.0
2023-08-28T12:31:43.293Z
@RiteshSingh  You could ask a new question in [Earth Science SE](https://earthscience.stackexchange.com/) for desert sand day/night oscillations in temperature as a function of depth similar to those for the Moon in my links.
uhoh
<the-moon><solar-system><natural-satellites><planetary-science><moonlanding>
What secondary and tertiary conclusions can be drawn from the temperature characteristics of lunar soil sent by ISRO Chandrayaan 3?
Ritesh Singh
# What secondary and tertiary conclusions can be drawn from the temperature characteristics of lunar soil sent by ISRO Chandrayaan 3?

(Asked by: username_0 on 2023-08-27)

[ISRO Chandrayaan 3](https://www.isro.gov.in/Chandrayaan3.html) [released](https://www.msn.com/en-in/news/techandscience/chandrayaan-3-chaste-payload-aboard-vikram-lander-measures-lunar-surface-temperature-how-it-works/ar-AA1fQey6) the following data today about the temperature characteristics of lunar soil.

[![enter image description here](https://i.sstatic.net/JyxKx.jpg)](https://i.sstatic.net/JyxKx.jpg)

1. What secondary and tertiary conclusions can be drawn it?
2. More specifically, what may be the possible reasons for the rapid drop in temperature from 55 C to -10 C in just 8 cm?

*Clarification: I do not claim it to be correct usage but here is what I meant: Primary conclusions are those that are directly visible from the data. Secondary conclusions build on the primary ones, and so on.*

**Tags:** the-moon, solar-system, natural-satellites, planetary-science, moonlanding
> **Comments:**
> **username_1**: That the material is not very conductive and the surface is exposed to the Sun?  
> **username_2**: I'm familiar with the notion of "secondary and tertiary" sources.  I'm not familiar with the notion of secondary and tertiary conclusions.  Perhaps I'm the only one here who doesn't know what you mean by this, but could you explain?  
> **username_3**: potentially helpful [this answer to *Do we know the fluctuations and constant temperature depth of the moon?*](https://astronomy.stackexchange.com/a/30532/7982) The area is obviously sunlit at the moment so the top half meter (plus/minus) of loose regolith will be warmer than below. Once it becomes night, that line will look totally different; the bottom will move *a little* to the left (colder) but the top will drop way way down in temperature. This exercise determines the thermal conductivity of this layer. Since a mission to the pole is all about temperature, it's potentially useful info.  
> **username_0**: @JamesK I do not claim it to be correct usage but here is what I meant: Primary conclusions are those that are directly visible from the data. Secondary conclusions build on the primary ones, and so on. As an example, ProfRob's comment can be called primary, any specific conclusions about the composition can be called secondary, futher conclusions about the origin and creation history can be called tertiary. (Added this clarification to the question.)  
> **username_0**: @uhoh Thank you, as always! But why is the temperature gradient on Earth not so sharp? Added this to the question as well.  
> **username_1**: Can you add a comparable temperature profile for the Earth if you are to include a further question?  
> **username_0**: @ProfRob Ok sir, I am removing the additional question and accepting your answer since it is complete for the previous question. I will find a similar profile for Earth and ask a separate question.  
> **username_3**: @RiteshSingh *Great (new) question!* For dry sand in the desert you really may see a similar phenomenon, but not nearly as extreme for several reasons. Here's a few: 1) day/night cycles are 27 times faster, 2) the Earth's atmosphere cools the hot sand and warms the cold sand (it's not exposed to the "cold vacuum" of space directly 3) air between the grains can conduct heat (not just the point-to-point sand grain contact) and any water vapor will conduct even more.  
> **username_3**: @RiteshSingh  You could ask a new question in [Earth Science SE](https://earthscience.stackexchange.com/) for desert sand day/night oscillations in temperature as a function of depth similar to those for the Moon in my links.  

---

## 1 answers

### Answer by username_1 on 2023-08-28. Score: 3 | Accepted answer

Looking at it with minimal prior knowledge, I think you expect that behaviour if you are on a surface that is sunlit (or recently sunlit) on a body that has no atmosphere.

The very top surface is hot because it absorbs sunlight. It can achieve an equilibrium temperature by radiating this heat back into space or conducting it below the surface.
Since there is no atmosphere, then cooling via convection (as would happen on the Earth is not an option).

If the thermal conductivity is low and the top surface receives of order 1 kW/m$^2$ (assuming a low albedo), then the surface radiates at a temperature given by
$$\sigma T^4 \simeq 1000\ ,$$,
where $\sigma$ is the Stefan-Boltzmann constant equal to $5.7\times 10^{-8}$ in SI units. This would give $T=364$ K (91C), which will be an upper limit because some light is reflected and since Chandrayaan-3 is at the lunar south pole, the sunlight comes in at an angle that probably reduces the flux from my estimate.

If the thermal conductivity is low, and there is no atmosphere or other fluid to transfer the heat downwards, then the temperature will drop rapidly with depth until it reaches the equilibrium temperature of the Moon as a whole. This will be a rough baseline temperature that could be estimated by assuming the Moon as a whole must on average radiate all the sunlight absorbed. Again, ignoring albedo,
$$4\pi R^2 \sigma T^4 = 1200 \pi R^2\ ,$$
where $R$ is the lunar radius (which cancels) and 1200 W/m$^2$ is the flux of sunlight incident normally on an object at the distance of the Moon from the Sun, with roughly 10% reflected back into space (the lunar albedo). This gives $T\simeq 269$ K (-4C). This is probably an overestimate if heat transport within the Moon is ineffective, since the lunar south pole will receive less than its fair share of this flux.

Thus I would expect to see a sunlit temperature profile as in the picture, with a high temperature at the surface reducing to minus a few Celsius at depth, but for that trend to reverse when the surface is not illuminated. i.e. For the surface to be well below zero Celsius and colder than the interior, which will remain at minus a few Celsius. That is because the surface can radiate more efficiently than heat can be brought to the surface by thermal conduction.

The surface gradients on Earth will generally not be as sharp because Earth has an atmosphere and other fluids that are able to transport heat much more effectively over these short distances and to cool the surface. The equilibrium temperature of the Earth (i.e. the baseline temperature) is also higher than the Moon because of its atmosphere. I would guess that the closest you would get to lunar conditions would be in a desert, where it is very dry.


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