<h2>It may not be possible for Venus to become tidal locked</h2>
<p>I don't think we know if it's possible for Venus to become tidally locked. <a href="https://arxiv.org/abs/0808.1071" rel="noreferrer">Correia et al.</a> 2008</p>
<blockquote>
<p>expect the equilibrium rotation to differ from the synchronous motion</p>
</blockquote>
<p>for planets like Venus with thick atmospheres relatively close to the Sun.</p>
<p>This might be best illustrated with a graphic from <a href="https://arxiv.org/abs/1611.05678" rel="noreferrer">Auclair-Desrotour et al.</a> 2016:</p>
<p><a href="https://i.sstatic.net/SP2wC.png" rel="noreferrer"><img src="https://i.sstatic.net/SP2wC.png" alt="enter image description here" /></a></p>
<p>The gravitational torque is driving towards a tidal lock, but the thermal atmospheric derived torque is in opposition.</p>
<p>Observations may show that Venus is slowing down, according to this <a href="https://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Could_Venus_be_shifting_gear" rel="noreferrer">esa article</a>. However, according to the article,</p>
<blockquote>
<p>the planet could have weather cycles stretching over decades, which
could lead to equally long-term changes in the rotation period</p>
</blockquote>
<h2>A tidal-locked Venus might not have big day/night temperature variation</h2>
<p>This article: <a href="https://manyworlds.space/2019/01/31/the-gale-winds-of-venus-suggest-how-locked-exoplanets-could-escape-a-fate-of-extreme-heat-and-brutal-cold/" rel="noreferrer">The Gale Winds of Venus Suggest How Locked Exoplanets Could Escape a Fate of Extreme Heat and Brutal Cold</a> suggests that the super-fast winds of Venus could occur even if Venus was tidally locked.  These winds exceed 100 m/s, which, according to the article is 60 times the surface rotation speed.  Even though Venus has an incredibly slow rotation rate currently (~243 days) the difference between night and day temperatures is very small.  We wouldn't expect much more deviation if Venus became tidally locked, as the heat transport is primarily driven through various other transport mechanisms than the Sun.  A relatively small amount of the Sun's energy makes it to the surface of Venus.</p>
<p><strong>Edit:</strong>
In the comments, uhoh asks about the super-fast winds of Venus:</p>
<blockquote>
<p>Is this mechanism keeping Venus' back side warm discussed anywhere in
a peer-reviewed state[...]?</p>
</blockquote>
<p>As a quote from <a href="https://science.sciencemag.org/content/368/6489/405" rel="noreferrer">Horinouchi et al.</a> (the &quot;SR&quot; in the quote refers to Super-Rotation, which is the super-fast winds):</p>
<blockquote>
<p>SR may also occur in tidally locked exoplanets—those that always face
the same way toward their host star and are therefore heated only on
one side. Zonal (east-west) flow around the rotation axis, including
SR, can transport heat from the dayside to the nightside of those
exoplanets</p>
</blockquote>
<p><a href="https://arxiv.org/abs/1103.3101" rel="noreferrer">Showman and Polvani</a> go into greater detail in their paper: <em>Equatorial superrotation on tidally locked exoplanets.</em></p>

CC BY-SA 4.0
2021-05-17T18:01:32.797Z
What is atmospheric tide? If it is due to warm expanded air, its density should be less that of cold air, so its effect should be opposite
Anixx
CC BY-SA 4.0
2021-05-17T18:03:03.703Z
Where a tidally locked planet will get the rotational moment for rotating atmosphere from?
Anixx
CC BY-SA 4.0
2021-05-17T18:08:47.600Z
"Atmospheric thermal tides are planetary-scale waves forced by the variation in absorption of solar radiation from day to night."- https://authors.library.caltech.edu/11565/1/PECjas84.pdf
Connor Garcia
CC BY-SA 4.0
2021-05-17T18:12:01.533Z
But tidally locked planets have no day and night
Anixx
CC BY-SA 4.0
2021-05-17T18:18:02.323Z
@Anixx Yes, but Venus currently does have day and night.  For a tidally locked (synchronous) planet, the initial conditions to drive super-rotating winds may be circulations caused by slight heat differences on the planet surface. According to the linked "Many Worlds" article.
Connor Garcia
CC BY-SA 4.0
2021-05-17T18:24:40.117Z
Where will it get rotating moment for rotating atmosphere?
Anixx
CC BY-SA 4.0
2021-05-17T21:14:25.183Z
I'm curious about how winds could move heat from the day to the night side of a tidally locked Venus. Symmetry arguments suggest to me naively that there couldn't be *prevailing winds* (easterly, or westerly) since there is now no preferred direction. Do the authors say *in which direction* the "superfast winds" of 100 m/s would circulate around the planet? Is this mechanism keeping Venus' back side warm discussed anywhere in a peer-reviewed state, or is it only presented in this person's blog post?
uhoh
CC BY-SA 4.0
2021-05-17T22:15:57.677Z
@uhoh A response may take several comments. The four day upper atmospheric circulation of Venus is well documented  since Mariner 10.  This paper: https://arxiv.org/abs/1709.03676 has a few explanations and a decent list of citations to other similar papers about the super-fast winds.  The winds are in the retrograde direction.
Connor Garcia
CC BY-SA 4.0
2021-05-17T22:21:41.540Z
@ConnorGarcia but **after Venus is tidally locked** words like "retrograde" no longer have the same meaning. In the absence of a preferred direction I think there will be stagnation and no big circulation patterns, because how would they know if they should go east or west?
uhoh
CC BY-SA 4.0
2021-05-17T22:32:32.787Z
@uhoh I think retrograde would still have meaning if Venus was tidal locked, since tidal locking is by definition pro-grade, right?
Connor Garcia
CC BY-SA 4.0
2021-05-17T23:21:31.730Z
@uhoh, I made an edit to reference a couple peer reviewed papers.  Also, it appears the winds are always retrograde.
Connor Garcia
CC BY-SA 4.0
2021-05-17T23:29:54.690Z
I said "no longer have the same meaning". I think there can be some bifurcation of the definition of pro/retro wind directions under certain special circumstances, but haven't had sufficient coffee this morning to prove it. But mostly I simply forgot that a tidally locked planet of course rotates with a period of 1 year. But I'm going to stick by my insertion of the word "same" in that sentence in order to not look overly ignorant. *Thanks for the links!* I will read them today.
uhoh
CC BY-SA 4.0
2023-06-17T14:51:31.157Z
How isn't Venus tidally locked? Its rotational and orbital periods are nearly the same (243 days and 225 days respectively).
Snack Exchange
CC BY-SA 4.0
2023-06-17T17:21:17.133Z
They have to be exactly the same to be tidally locked.
Connor Garcia
CC BY-SA 4.0
2021-05-17T17:53:55.023Z
2021-05-17T23:19:05.203Z
2021-05-17T23:19:05.203Z
Connor Garcia
<p>Suppose, Venus becomes tidally locked. Will its dark side cool enough so that the CO<sub>2</sub> from the atmosphere to precipitate in liquid form to make an ocean?</p>
<p>Also, I wonder, how close Venus is to becoming tidally locked? Does it accelerate or slow down its rotation?</p>

CC BY-SA 4.0
2021-05-17T21:06:56.113Z
There is no liquid form of CO2 at the pressures and temperatures.
planetmaker
CC BY-SA 4.0
2021-05-17T21:10:52.730Z
very *cool* question! (pun intended)
uhoh
<solar-system><planetary-atmosphere><tidal-forces><tidal-locking><climate>
Tidally locked Venus, is it possible and consequences?
Anixx
# Tidally locked Venus, is it possible and consequences?

(Asked by: username_0 on 2021-05-17)

Suppose, Venus becomes tidally locked. Will its dark side cool enough so that the CO2 from the atmosphere to precipitate in liquid form to make an ocean?

Also, I wonder, how close Venus is to becoming tidally locked? Does it accelerate or slow down its rotation?

**Tags:** solar-system, planetary-atmosphere, tidal-forces, tidal-locking, climate
> **Comments:**
> **username_1**: There is no liquid form of CO2 at the pressures and temperatures.  
> **username_2**: very *cool* question! (pun intended)  

---

## 1 answers

### Answer by username_3 on 2021-05-17. Score: 8 | Accepted answer

## It may not be possible for Venus to become tidal locked

I don't think we know if it's possible for Venus to become tidally locked. [Correia et al.](https://arxiv.org/abs/0808.1071) 2008

> expect the equilibrium rotation to differ from the synchronous motion

for planets like Venus with thick atmospheres relatively close to the Sun.

This might be best illustrated with a graphic from [Auclair-Desrotour et al.](https://arxiv.org/abs/1611.05678) 2016:

[![enter image description here](https://i.sstatic.net/SP2wC.png)](https://i.sstatic.net/SP2wC.png)

The gravitational torque is driving towards a tidal lock, but the thermal atmospheric derived torque is in opposition.

Observations may show that Venus is slowing down, according to this [esa article](https://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Could_Venus_be_shifting_gear). However, according to the article,

> the planet could have weather cycles stretching over decades, which
> could lead to equally long-term changes in the rotation period

## A tidal-locked Venus might not have big day/night temperature variation

This article: [The Gale Winds of Venus Suggest How Locked Exoplanets Could Escape a Fate of Extreme Heat and Brutal Cold](https://manyworlds.space/2019/01/31/the-gale-winds-of-venus-suggest-how-locked-exoplanets-could-escape-a-fate-of-extreme-heat-and-brutal-cold/) suggests that the super-fast winds of Venus could occur even if Venus was tidally locked. These winds exceed 100 m/s, which, according to the article is 60 times the surface rotation speed. Even though Venus has an incredibly slow rotation rate currently (~243 days) the difference between night and day temperatures is very small. We wouldn't expect much more deviation if Venus became tidally locked, as the heat transport is primarily driven through various other transport mechanisms than the Sun. A relatively small amount of the Sun's energy makes it to the surface of Venus.

**Edit:**
In the comments, uhoh asks about the super-fast winds of Venus:

> Is this mechanism keeping Venus' back side warm discussed anywhere in
> a peer-reviewed state[...]?

As a quote from [Horinouchi et al.](https://science.sciencemag.org/content/368/6489/405) (the "SR" in the quote refers to Super-Rotation, which is the super-fast winds):

> SR may also occur in tidally locked exoplanets—those that always face
> the same way toward their host star and are therefore heated only on
> one side. Zonal (east-west) flow around the rotation axis, including
> SR, can transport heat from the dayside to the nightside of those
> exoplanets

[Showman and Polvani](https://arxiv.org/abs/1103.3101) go into greater detail in their paper: *Equatorial superrotation on tidally locked exoplanets.*

> **Comments:**
> **username_0**: What is atmospheric tide? If it is due to warm expanded air, its density should be less that of cold air, so its effect should be opposite  
> **username_0**: Where a tidally locked planet will get the rotational moment for rotating atmosphere from?  
> **username_3**: "Atmospheric thermal tides are planetary-scale waves forced by the variation in absorption of solar radiation from day to night."- https://authors.library.caltech.edu/11565/1/PECjas84.pdf  
> **username_0**: But tidally locked planets have no day and night  
> **username_3**: @Anixx Yes, but Venus currently does have day and night.  For a tidally locked (synchronous) planet, the initial conditions to drive super-rotating winds may be circulations caused by slight heat differences on the planet surface. According to the linked "Many Worlds" article.  
> **username_0**: Where will it get rotating moment for rotating atmosphere?  
> **username_2**: I'm curious about how winds could move heat from the day to the night side of a tidally locked Venus. Symmetry arguments suggest to me naively that there couldn't be *prevailing winds* (easterly, or westerly) since there is now no preferred direction. Do the authors say *in which direction* the "superfast winds" of 100 m/s would circulate around the planet? Is this mechanism keeping Venus' back side warm discussed anywhere in a peer-reviewed state, or is it only presented in this person's blog post?  
> **username_3**: @uhoh A response may take several comments. The four day upper atmospheric circulation of Venus is well documented  since Mariner 10.  This paper: https://arxiv.org/abs/1709.03676 has a few explanations and a decent list of citations to other similar papers about the super-fast winds.  The winds are in the retrograde direction.  
> **username_2**: @ConnorGarcia but **after Venus is tidally locked** words like "retrograde" no longer have the same meaning. In the absence of a preferred direction I think there will be stagnation and no big circulation patterns, because how would they know if they should go east or west?  
> **username_3**: @uhoh I think retrograde would still have meaning if Venus was tidal locked, since tidal locking is by definition pro-grade, right?  
> **username_3**: @uhoh, I made an edit to reference a couple peer reviewed papers.  Also, it appears the winds are always retrograde.  
> **username_2**: I said "no longer have the same meaning". I think there can be some bifurcation of the definition of pro/retro wind directions under certain special circumstances, but haven't had sufficient coffee this morning to prove it. But mostly I simply forgot that a tidally locked planet of course rotates with a period of 1 year. But I'm going to stick by my insertion of the word "same" in that sentence in order to not look overly ignorant. *Thanks for the links!* I will read them today.  
> **username_4**: How isn't Venus tidally locked? Its rotational and orbital periods are nearly the same (243 days and 225 days respectively).  
> **username_3**: They have to be exactly the same to be tidally locked.  

---

