Tidally-locked planets flipping around their axes

[Strato Incendus]

Recently, I’ve heard from Anton Petrov on YouTube that some tidally-locked planets around red-dwarf stars (such as TRAPPIST-1) have been suspected to flip around their own axis every once in a while — so that the former day side becomes the night side, and vice versa.

This is presumed to happen for the same reason as why a T handle set in a rotating motion on a space station starts flipping back and forth. The latter is an issue we discussed for spaceship designs, when it came to how multiple rings have to be arranged in counter-rotating pairs, in order to prevent the ship from flipping around its axis during travel.
I’m wondering what this would do to the presumably habitable twilight zone of a tidally-locked planet. If the day and night side swap places, but the twilight zone remains in place, the twilight zone could remain habitable, as far as I can tell. The question is in which direction the planet flips:

1) If the planet flips around its axis along the plane of motion, the habitable vertical belt that is the twilight zone would essentially be “rolling” on the circumference of the orbit. Meaning, none of the twilight zone would move into being on the day side or night side temporarily.

2) If however the planet flips around its axis in a 90-degree angle to the plane of motion, the poles of the planet, normally in the twilight zone, would temporarily point towards the star or away from it. Meaning, one of the poles would become the day side, the other pole the night side for a while. The rest of the twilight zone — the part always pointing away from the star at a 90-degree angle — would remain in the twilight area.
In my story, the planet in question is Teegarden b. The question is now whether I have to postulate that it doesn’t do these flips, or whether I can acknowledge the flips, but claim it doesn’t matter as long as you only settle in the (right parts of) the twilight zone. The day side and night side are uninhabitable anyway.

Anton Petrov demonstrated the potentially catastrophic consequences of such a flip with Earth in Universe Sandbox 2: In scenario 1, Africa was the day side; then, he flipped the planet around, and suddenly South America was the day side, and Africa was the night side. I don’t recall if there were any places on Earth in that test which would have remained habitable in either scenario, AND in the transitionary period in between.

 

[Hornbein]

2) If however the planet flips around its axis in a 90-degree angle to the plane of motion, the poles of the planet, normally in the twilight zone, would temporarily point towards the star or away from it. Meaning, one of the poles would become the day side, the other pole the night side for a while. The rest of the twilight zone — the part always pointing away from the star at a 90-degree angle — would remain in the twilight area.

This is what happens. A tidally locked planet rotates once a year. The axis of rotation is what flips, and that's perpendicular to the plane of motion.

 

[Hornbein]

2) If however the planet flips around its axis in a 90-degree angle to the plane of motion, the poles of the planet, normally in the twilight zone, would temporarily point towards the star or away from it. Meaning, one of the poles would become the day side, the other pole the night side for a while. The rest of the twilight zone — the part always pointing away from the star at a 90-degree angle — would remain in the twilight area.

This is what happens. A tidally locked planet rotates once a year. The axis of rotation is what flips, and that's perpendicular to the plane of motion.

Look at this a bit more carefully, only the two segments of the twilight zone that are on the equator remain in the twilight zone during a flip. That's where any permanent settlements would have to be.

I wonder how fast these planetary flips. Year? Century? Other planets are involved, so I guess the flips wouldn't be all that predictable.

 

[Algr]

So the planet rotates 90°? The "sun pole" becomes a north or south pole? The video I've seen looks more like like a 180° flip.

Life on such planets would have evolved to deal with such flips. I'd expect huge wind storms and rushes of water for seeds and organisms to catch a ride upon. The nightside glaciers would melt and flow back to the new nightside. This would reduce the hotside temperatures for a long time. I wonder if frozen lifeforms could revive thousands of years later when the next flip happens?

 

[Algr]

Can you link to the Anton Petrov video? I don't see it on his YouTube page.

 

[Strato Incendus]

Sure, here it is:

 

[Algr]

Anton's video has the twilight zone passing through the poles in both the normal and inverted Earth. (180°) But the ice cap covers more than half the Earth, so both remain frozen in both orientations. It looks like the poles remain poles in both orientations, rather than Antarctica becoming a sun or night pole.

To avoid this in your story, you could just say that the planet lacks close neighbors, or is stabilized by some nature of its core that you never clearly define.

 

[Strato Incendus]

Nice idea, but that would still require me to change the destination planet. Because the one where I’m currently sending my ship, Teegarden b, has already been confirmed to have a close neighbour, Teegarden c.

So should I pick another planet in a distance of about 12.5 light years? Teegarden b is still the one with the highest Earth-Similarity Index (ESI) in Earth’s vicinity. There is only one planet with an even higher ESI, but it’s so far away that it’s not a realistic target for below-light-speed travel.

 

[Algr]

Stick with Teegarden b and go with the undefined "nature of it's core". Its neighbors boost it's magnetic field instead of flipping it. Don't dwell on the science. If you have an interesting story that readers want to believe in, and characters they like, readers won't sweat the details. Trek and Star Wars aren't enduring for their scientific accuracy, after all.

 

[Strato Incendus]

Alright, thanks a lot for your answers!

 

[Nik_2213]

Is this akin to how Mars' axal tilt may vary enough over 'deep time' for precession to potentially thaw its polar caps ?

Where-as Earth's is constrained by Moon's tidal dissipation ??

 

[Hornbein]

Stick with Teegarden b and go with the undefined "nature of it's core". Its neighbors boost it's magnetic field instead of flipping it. Don't dwell on the science. If you have an interesting story that readers want to believe in, and characters they like, readers won't sweat the details. Trek and Star Wars aren't enduring for their scientific accuracy, after all.

While this is a lot to like, I'm going to go the other way. Sometimes the scientific details lead the author to things they would never have imagined. That happened to me. On the other hand, I'm not a popular writer nor am I trying to be.

 

[Algr]

It turns out this is Trappist 1c, not Teegarden b: But if you use a real planet this could happen to you someday soon:



So I'm right the first time and ignore the second. Use an imaginary planet so that some future telescope doesn't pluto your book.

 

[EventHorizon]

Is this akin to how Mars' axal tilt may vary enough over 'deep time' for precession to potentially thaw its polar caps ?

Where-as Earth's is constrained by Moon's tidal dissipation ??

Mars's obliquity changes substantially on timescales of hundreds of thousands of millions of years. So if a planet like Mars has life, I think the life would have enough time to adapt to the changes