<p><a href="http://science.sciencemag.org/content/347/6222/632">Leconte et al. (2015)</a> suggested that the presence of an atmosphere could prevent or at least slow tidal locking. The star should exert two separate torques: one on the atmosphere and one on the solid body of the planet:
$$T_a=-\frac{3}{2}K_ab_a(2\omega-2n),\quad T_g=-\frac{3}{2}K_gb_g(2\omega-2n)$$
where
$$K_a\equiv\frac{3M_*R_p^3}{5\bar{\rho}a^3},\quad K_g\equiv\frac{GM_*R_p^5}{a^6}$$
for stellar mass $M_*$, planetary radius $R_p$, mean density $\rho$, semi-major axis $a$, mean motion $n$, rotation rate $\omega$, and response to torques $b_a$ and $b_g$. The two torques could be equal, and assuming that the atmosphere transfers some angular momentum to the surface of the planet, this could prevent tidal locking. There are several equilibria at which this could occur:</p>

<p><a href="https://i.sstatic.net/87Wrk.jpg"><img src="https://i.sstatic.net/87Wrk.jpg" alt="enter image description here"></a></p>

CC BY-SA 3.0
2017-02-03T17:25:48.253Z
Would I be wrong to say this is very possibly occurring on Venus?
userLTK
CC BY-SA 3.0
2016-11-12T16:38:41.330Z
2016-11-12T16:38:41.330Z
HDE 226868
<p>The more likely case is actually a spin-orbit resonance that is <em>not</em> 1:1 but a half odd multiple, like the 3:2 case of our own Mercury.  Having eccentricity in the orbit encourages this situation.</p>

<p>I’ve been meaning to write this up on the Worldbuilding.SE but I have not re-found enough references.  But see <a href="http://www.seti.org/weeky-lecture/patterns-sunlight-extra-solar-planets">this video</a>.</p>

CC BY-SA 3.0
2016-11-19T12:23:17.737Z
very exciting video. U should have posted that information on WB, what if I didn't looked here?
MolbOrg
CC BY-SA 3.0
2017-02-03T17:33:00.983Z
Mercury is a great example, and around a red-dwarf with a shorter orbital period (like the 11 day period of proxima centauri b), with a mercury orbit that would be 264 hours of sun, 264 hours of night.   Not ideal, but a happy medium between Earth's 12 hours of sunlight and Mercury's several months.
userLTK
CC BY-SA 3.0
2016-11-13T12:17:14.613Z
2016-11-13T12:17:14.613Z
JDługosz
<p>Tidal locking necessarily requires mass asymmetry. In planet formation central limit theory suggests many uniform density/mass planets are formed around red dwarf stars as their rotation initially does not match their revolution. As such worlds become locked, their water mass will migrate from the hot side and freeze on the cold side in Everest mass mountains. This will disrupt the tidal locking and cause a reversal. A resonance of such cycles could cause very long day/night cycles on such 'tidally locked' worlds. Angular monentum tells us that surface mass is much more significant than mass near the core.  This could have significant implications for life.</p>

CC BY-SA 4.0
2022-11-16T02:56:03.537Z
2022-11-16T02:56:03.537Z
aaa_clem
<p>If the star is large enough and the habitable zone is able to extend quite a bit outwards and the planet orbits the outer edge of that habitable zone then yes.</p>

CC BY-SA 4.0
2021-06-26T14:53:00.180Z
2021-06-26T14:53:00.180Z
Grey ideas the The liopurodon4
<p>Yes: It has a companion planet or an excessively large moon, with the two bodies orbiting their common center of mass (much like the Earth and the Moon). They could be tidally-locked to each other, but they cannot be tidally-locked to their star.</p>

CC BY-SA 3.0
2016-11-13T19:57:34.850Z
Can you provide some evidence for why this would work? Why couldn't it be that each body becomes tidally locked with the star first, thus preventing the planets from being tidally locked with one another?
HDE 226868
CC BY-SA 3.0
2016-11-14T14:17:00.147Z
I don't believe this answer is deserving of being the best answer. It does not attempt to validate or cite references for its statements. After all, anyone can say anything on the internet. I would prefer more proof for the statements above.
zephyr
CC BY-SA 3.0
2017-02-03T21:18:27.343Z
@JDługosz Iván can't edit yet.
Tim
CC BY-SA 3.0
2017-02-04T05:11:45.153Z
I thought anyone can edit; it just goes to the review queue.
JDługosz
CC BY-SA 3.0
2016-11-12T21:07:09.217Z
2017-02-03T22:14:34.417Z
2017-02-03T22:14:34.417Z
PMar
<p>Is there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?</p>

<p>For example, could a planet with a 90° obliquity and large moon avoid such a situation?</p>

CC BY-SA 4.0
2020-07-06T15:06:20.897Z
BTW I don't think tidally locked terrestrial planets orbiting in a red dwarf star's habitable zone would be completely uninhabitable. The planet will still be rotating with a period equal to its orbital period, which for red dwarfs is on the order of several days or weeks. This seems fast enough for atmospheric circulation to redistribute heat and prevent the atmosphere freezing out on the night side.
RobertF
<orbit><tidal-forces><celestial-mechanics><red-dwarf>
Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?
Soba
# Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

(Asked by: username_0 on 2016-11-12)

Is there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?

For example, could a planet with a 90° obliquity and large moon avoid such a situation?

**Tags:** orbit, tidal-forces, celestial-mechanics, red-dwarf

> **Comments:**
> **username_1**: BTW I don't think tidally locked terrestrial planets orbiting in a red dwarf star's habitable zone would be completely uninhabitable. The planet will still be rotating with a period equal to its orbital period, which for red dwarfs is on the order of several days or weeks. This seems fast enough for atmospheric circulation to redistribute heat and prevent the atmosphere freezing out on the night side.  

---

## 5 answers

### Answer by username_8 on 2016-11-12. Score: 8 | Accepted answer

Yes: It has a companion planet or an excessively large moon, with the two bodies orbiting their common center of mass (much like the Earth and the Moon). They could be tidally-locked to each other, but they cannot be tidally-locked to their star.

> **Comments:**
> **username_2**: Can you provide some evidence for why this would work? Why couldn't it be that each body becomes tidally locked with the star first, thus preventing the planets from being tidally locked with one another?  
> **username_9**: I don't believe this answer is deserving of being the best answer. It does not attempt to validate or cite references for its statements. After all, anyone can say anything on the internet. I would prefer more proof for the statements above.  
> **username_10**: @username_4 Iván can't edit yet.  
> **username_4**: I thought anyone can edit; it just goes to the review queue.  

---

### Answer by username_2 on 2016-11-12. Score: 14

[Leconte et al. (2015)](http://science.sciencemag.org/content/347/6222/632) suggested that the presence of an atmosphere could prevent or at least slow tidal locking. The star should exert two separate torques: one on the atmosphere and one on the solid body of the planet:
$$T\_a=-\frac{3}{2}K\_ab\_a(2\omega-2n),\quad T\_g=-\frac{3}{2}K\_gb\_g(2\omega-2n)$$
where
$$K\_a\equiv\frac{3M\_\*R\_p^3}{5\bar{\rho}a^3},\quad K\_g\equiv\frac{GM\_\*R\_p^5}{a^6}$$
for stellar mass $M\_\*$, planetary radius $R\_p$, mean density $\rho$, semi-major axis $a$, mean motion $n$, rotation rate $\omega$, and response to torques $b\_a$ and $b\_g$. The two torques could be equal, and assuming that the atmosphere transfers some angular momentum to the surface of the planet, this could prevent tidal locking. There are several equilibria at which this could occur:

[![enter image description here](https://i.sstatic.net/87Wrk.jpg)](https://i.sstatic.net/87Wrk.jpg)

> **Comments:**
> **username_3**: Would I be wrong to say this is very possibly occurring on Venus?  

---

### Answer by username_4 on 2016-11-13. Score: 6

The more likely case is actually a spin-orbit resonance that is *not* 1:1 but a half odd multiple, like the 3:2 case of our own Mercury. Having eccentricity in the orbit encourages this situation.

I’ve been meaning to write this up on the Worldbuilding.SE but I have not re-found enough references. But see [this video](http://www.seti.org/weeky-lecture/patterns-sunlight-extra-solar-planets).

> **Comments:**
> **username_5**: very exciting video. U should have posted that information on WB, what if I didn't looked here?  
> **username_3**: Mercury is a great example, and around a red-dwarf with a shorter orbital period (like the 11 day period of proxima centauri b), with a mercury orbit that would be 264 hours of sun, 264 hours of night.   Not ideal, but a happy medium between Earth's 12 hours of sunlight and Mercury's several months.  

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### Answer by username_6 on 2022-11-16. Score: 1

Tidal locking necessarily requires mass asymmetry. In planet formation central limit theory suggests many uniform density/mass planets are formed around red dwarf stars as their rotation initially does not match their revolution. As such worlds become locked, their water mass will migrate from the hot side and freeze on the cold side in Everest mass mountains. This will disrupt the tidal locking and cause a reversal. A resonance of such cycles could cause very long day/night cycles on such 'tidally locked' worlds. Angular monentum tells us that surface mass is much more significant than mass near the core. This could have significant implications for life.


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### Answer by username_7 on 2021-06-26. Score: 0

If the star is large enough and the habitable zone is able to extend quite a bit outwards and the planet orbits the outer edge of that habitable zone then yes.


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