<p>There are several ways to look at this.</p>
<p>One rather simple way is to compute the Rayleigh number of Mars' mantle. The <a href="https://en.wikipedia.org/wiki/Rayleigh_number" rel="nofollow noreferrer">Rayleigh number</a> is a dimensionless number defined as:</p>
<p><span class="math-container">$Ra = \dfrac{\rho g \alpha \Delta T d^3}{\eta \kappa}$</span></p>
<p>where <span class="math-container">$\rho$</span> is the mantle density, <span class="math-container">$g$</span> is gravitational acceleration, <span class="math-container">$\alpha$</span> is the thermal expansion coefficient, <span class="math-container">$\Delta T$</span> is the difference in temperature over the convective layer of thickness <span class="math-container">$d$</span>, <span class="math-container">$\eta$</span> is the viscosity, and <span class="math-container">$\kappa$</span> the thermal diffusivity. It is generally considered that convection happens when <span class="math-container">$Ra &gt; 1000$</span>, and higher <span class="math-container">$Ra$</span> mean more vigorous convection. <span class="math-container">$Ra$</span> for Mars is estimated at <span class="math-container">$10^6$</span> by <a href="https://doi.org/10.1093/acrefore/9780190647926.013.109" rel="nofollow noreferrer">Mulyukova &amp; Bercovici 2020</a> (compared to <span class="math-container">$10^7$</span> for the Earth), meaning that there is convection in Mars' mantle, although less vigorous than on Earth.</p>
<p>Another approach is to look at some geological features of Mars that can provide constraints on the internal dynamics of the planet. For example, recently active point-source volcanoes, such as Olympus Mons, suggest the presence of a mantle plume—thus convection—rising from beneath (<a href="https://doi.org/10.1029/2007GL030544" rel="nofollow noreferrer">Li &amp; Kiefer 2007</a>). Likewise, the presence of mantle plumes/convection can explain variations in lithospheric thickness (<a href="https://doi.org/10.1029/2009GL039827" rel="nofollow noreferrer">Kiefer &amp; Li 2009</a>).</p>
<p>A study by <a href="https://doi.org/10.1016/j.gsf.2017.06.004" rel="nofollow noreferrer">Stern et al. (2017)</a> used volcanisms, faults and impacts to define a &quot;Tectonic Activity Index&quot; (TAI) for 26 planetary bodies, ranging from 0 to 3. They found that Mars has a TAI of 2, less than the Earth and Venus (3), but still inferred to be &quot;tectonically and convectively active&quot; (bodies with TAI &lt; 2 are inferred to be tectonically dead). They think that Mars actually represents the transition between active and dead bodies:</p>
<blockquote>
<p>The present tectonic style of Mars represents an almost completely
stabilized stagnant lid [SL]. Here, a single upwelling mantle plume,
pouring lava out at the same sites for hundreds of millions of years,
produced the immense Tharsis rise and volcanoes (Zuber, 2001). When
these last few mantle plumes are extinguished, tectonic style
transitions to the final SL stage – planetoid death. This stage is
typified by Mercury and Earth's moon, bodies with ultra-thick,
ultra-stable lithospheres</p>
</blockquote>
<p><a href="https://i.sstatic.net/Y0JYk.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Y0JYk.jpg" alt="enter image description here" /></a>
<em>Possible evolution of magmatotectonic styles for a large silicate body, like the Earth. Plate tectonics requires certain conditions of lithospheric density and strength to evolve and is likely to be presaged and followed by stagnant lid tectonics.</em> After <a href="https://doi.org/10.1016/j.gsf.2017.06.004" rel="nofollow noreferrer">Stern et al. (2017)</a> (CC BY-NC-ND 4.0)</p>

CC BY-SA 4.0
2021-01-19T15:44:58.290Z
2021-01-20T11:03:46.007Z
2021-01-20T11:03:46.007Z
Jean-Marie Prival
<p><a href="https://en.wikipedia.org/wiki/Mars#Internal_structure" rel="noreferrer">Mars</a> is differentiated, with a core, a mantle and a crust. There are no (longer any) plate tectonics on Mars. Does this mean there is no convection in the mantle? Could there be convection in the mantle without it causing plate tectonics?</p>

CC BY-SA 4.0
2021-01-08T18:19:50.903Z
Horribly written case for volcanic convection: https://www.studyprobe.live/2020/05/volcanic-convection-on-mars-evinced-by-pre-historic-meteorite.html   Case for vulcanism within last 50K to 200K years.  https://astrobites.org/2020/12/25/mars-modern-volcanism/
Wayfaring Stranger
CC BY-SA 4.0
2021-01-20T08:36:37.590Z
I also found [Degree-1 convection following a giant impact](http://www.mantleplumes.org/MarsDichotomy.html) worth a look. Even though it is about a different topic, I have the impression that it implies that convection does occur in the mantle due to impact (and without plate tectonics).
B--rian
<planet><mars><geology>
Is there convection in Mars' mantle?
usernumber
# Is there convection in Mars' mantle?

(Asked by: username_0 on 2021-01-07)

[Mars](https://en.wikipedia.org/wiki/Mars#Internal_structure) is differentiated, with a core, a mantle and a crust. There are no (longer any) plate tectonics on Mars. Does this mean there is no convection in the mantle? Could there be convection in the mantle without it causing plate tectonics?

**Tags:** planet, mars, geology

> **Comments:**
> **username_1**: Horribly written case for volcanic convection: https://www.studyprobe.live/2020/05/volcanic-convection-on-mars-evinced-by-pre-historic-meteorite.html   Case for vulcanism within last 50K to 200K years.  https://astrobites.org/2020/12/25/mars-modern-volcanism/  
> **username_2**: I also found [Degree-1 convection following a giant impact](http://www.mantleplumes.org/MarsDichotomy.html) worth a look. Even though it is about a different topic, I have the impression that it implies that convection does occur in the mantle due to impact (and without plate tectonics).  

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## 1 answers

### Answer by username_3 on 2021-01-19. Score: 10 | Accepted answer

There are several ways to look at this.

One rather simple way is to compute the Rayleigh number of Mars' mantle. The [Rayleigh number](https://en.wikipedia.org/wiki/Rayleigh_number) is a dimensionless number defined as:

$Ra = \dfrac{\rho g \alpha \Delta T d^3}{\eta \kappa}$

where $\rho$ is the mantle density, $g$ is gravitational acceleration, $\alpha$ is the thermal expansion coefficient, $\Delta T$ is the difference in temperature over the convective layer of thickness $d$, $\eta$ is the viscosity, and $\kappa$ the thermal diffusivity. It is generally considered that convection happens when $Ra > 1000$, and higher $Ra$ mean more vigorous convection. $Ra$ for Mars is estimated at $10^6$ by [Mulyukova & Bercovici 2020](https://doi.org/10.1093/acrefore/9780190647926.013.109) (compared to $10^7$ for the Earth), meaning that there is convection in Mars' mantle, although less vigorous than on Earth.

Another approach is to look at some geological features of Mars that can provide constraints on the internal dynamics of the planet. For example, recently active point-source volcanoes, such as Olympus Mons, suggest the presence of a mantle plume—thus convection—rising from beneath ([Li & Kiefer 2007](https://doi.org/10.1029/2007GL030544)). Likewise, the presence of mantle plumes/convection can explain variations in lithospheric thickness ([Kiefer & Li 2009](https://doi.org/10.1029/2009GL039827)).

A study by [Stern et al. (2017)](https://doi.org/10.1016/j.gsf.2017.06.004) used volcanisms, faults and impacts to define a "Tectonic Activity Index" (TAI) for 26 planetary bodies, ranging from 0 to 3. They found that Mars has a TAI of 2, less than the Earth and Venus (3), but still inferred to be "tectonically and convectively active" (bodies with TAI < 2 are inferred to be tectonically dead). They think that Mars actually represents the transition between active and dead bodies:

> The present tectonic style of Mars represents an almost completely
> stabilized stagnant lid [SL]. Here, a single upwelling mantle plume,
> pouring lava out at the same sites for hundreds of millions of years,
> produced the immense Tharsis rise and volcanoes (Zuber, 2001). When
> these last few mantle plumes are extinguished, tectonic style
> transitions to the final SL stage – planetoid death. This stage is
> typified by Mercury and Earth's moon, bodies with ultra-thick,
> ultra-stable lithospheres

[![enter image description here](https://i.sstatic.net/Y0JYk.jpg)](https://i.sstatic.net/Y0JYk.jpg)
*Possible evolution of magmatotectonic styles for a large silicate body, like the Earth. Plate tectonics requires certain conditions of lithospheric density and strength to evolve and is likely to be presaged and followed by stagnant lid tectonics.* After [Stern et al. (2017)](https://doi.org/10.1016/j.gsf.2017.06.004) (CC BY-NC-ND 4.0)


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