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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?

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  • $\begingroup$ There is no liquid form of CO2 at the pressures and temperatures. $\endgroup$
    – planetmaker
    May 17, 2021 at 21:06
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    $\begingroup$ very cool question! (pun intended) $\endgroup$
    – uhoh
    May 17, 2021 at 21:10

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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. 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. 2016:

enter image description here

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. 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 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. (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 go into greater detail in their paper: Equatorial superrotation on tidally locked exoplanets.

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  • $\begingroup$ 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 $\endgroup$
    – Anixx
    May 17, 2021 at 18:01
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    $\begingroup$ 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? $\endgroup$
    – uhoh
    May 17, 2021 at 21:14
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    $\begingroup$ @uhoh I think retrograde would still have meaning if Venus was tidal locked, since tidal locking is by definition pro-grade, right? $\endgroup$
    – Connor Garcia ♦
    May 17, 2021 at 22:32
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    $\begingroup$ @uhoh, I made an edit to reference a couple peer reviewed papers. Also, it appears the winds are always retrograde. $\endgroup$
    – Connor Garcia ♦
    May 17, 2021 at 23:21
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    $\begingroup$ 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. $\endgroup$
    – uhoh
    May 17, 2021 at 23:29

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