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I am developing a world, and I need to see what exactly the surface would be like. It is tidally locked at 1AU away from the parent star.

It is tidally-locked via being a Torus with a major radius of 1AU. When I say "tidally locked", I mean that despite the fact it rotates, the inside part of the Torus still always faces the sun.

Ignoring the effects of the Torus, what effects exactly would the sun have on such a tidally locked planet? Would it simply be too hot to be habitable?

Would be appreciated if sources could be given; but it is not a requirement.

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  • $\begingroup$ You can't just ignore the effects of the toroidal topology. You are effectively reducing day/night circulation to a 2 dimensional system rather than 3D, which invalidates all existing research on the climates of synchronously rotating worlds. There is probably a situation in which it would be habitable, but it's not at all obvious what the appropriate conditions would be. $\endgroup$ Jun 10 at 4:22

3 Answers 3

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The Good, the Bad, and the Ugly

Good: One side of the planet will be fundamentally uninhabitable. If you want the away-from-the-sun side to be habitable, move the planet closer to the sun. If you want the sun-side to be habitable, move it further away. In the case of your toroid, you'll have regions of the planet that are curiously habitable. For example, the sun-side may be too hot, but the sun-side center-of-the-torus might be just right, which means the other side of the inside will be warm, but likely habitable, while the far side of the torus might be too cold. You'll have sweeps of geography (cool, curving sweeps) wherein habitability is possible.

And I'm not even going to try to address the issue of climate on this world in detail. I suspect that if you land that planet smack dab in the middle of its ideal Goldilocks zone, the result will be a storm vortex in the doughnut hole that would impress even the angels in heaven....

Bad: But your real problem is that I suspect you're throwing science out the window (remember, you're using the tag). I could be wrong, but I don't believe a toroidal planet could be tidally locked. Tidal locking kinda depends on the spheroid having a somewhat homogeneous-enough density that the forces can balance permitting the lock. Your toroid doesn't have that. Someone with a lot more celestial mechanics than I have will need to get involved, but I don't think your question has enough of a science-based foundation to justify the tag.

Aaaaand the ugly... If we ignore the toroid as you suggest, then what remains is another "life on my tidally-locked planet" question. A bunch have been asked on this Stack, which would make your question a duplicate.... You sure you want to ignore the torus?

I just read @Halfthawed's answer. I like it and upvoted it. You should too. It does a good job of pointing out the one way a torus might, maybe, be tidally locked. However I'd like to beg to differ that the result would be an entirely uninhabitable planet. Technically Mars in in Sol's goldilocks zone, which would suggest you could move the tidally locked planet far enough back to permit its sun-side to be habitable. Maybe the consensus would be that it's scientifically impossible — but I believe it's well inside of suspension-of-disbelief possible.

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  • $\begingroup$ As I said before, I worded myself badly when I said "tidally-locked", but ultimately, it has the same effects of being tidally locked. That is, one side always faces the sun. That being the inner part of the torus. Thus, the way I was using it, a Torus around a Star can only be tidally-locked. And it does have science-basis in toroidal planets being scientifically supported in how they can possibly form, and I have done the math in the necessary rotation period to produce the proper gravity. $\endgroup$
    – Zoey
    Jun 10 at 23:41
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Ignoring the effects of the Torus, what effects exactly would the sun have on such a tidally locked planet? Would it simply be too hot to be habitable?

It would not be habitable. And the exact science is slightly beyond my pay grade, but I shall do my best. A toroidal planet is only possible as either a Maclaurin spheroid or a Jacobi ellipsoid, most likely here a Jacobi, but that's so so important right as the angular momentum. The angular momentum on such an object moves across the ring - otherwise it will not hold stability! Now, in order to have such an object be tidally locked, the angular momentum must be perfectly perpendicular to the planet's orbit around the sun.

In Earth terms, this would means that the planet would have a rotation axis of 90 degrees with the North Pole pointed at the Sun. You may think about it that way.

Under normal circumstances (i.e. not tidally locked), this configuration is quasistable at best. But with a tidally locked planet, one side superheats. And superheating is chaotic - and chaos means imperfection. And herein lies the rub when it comes to this quasistable configuration - any imperfection cannot be corrected, and indeed the presence of any one will lead to it getting larger, meaning that it is only a matter of time before the planet collapsed into itself and assumes a traditional sphere.

Placing it far enough in orbit to render the heat unable to create such an irregularity will also render it uninhabitable because it will be out of the narrow goldilocks zone and simply too cold. Additionally, since the planet's orbit is not in concert with the angular momentum, it will apply itself to the angular momentum and induce irregularities as well. In short, this is simply too unstable except as a highly artificial world (i.e. ringworld.)

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  • $\begingroup$ I said what I meant I thought, that it did spin normally. I just meant the inside always faces the sun. So I apologize if I didn't make that clear. I have actually calculated the rotation period necessary to get the gravity I wanted. $\endgroup$
    – Zoey
    Jun 10 at 3:38
  • $\begingroup$ @Zoey If by that you mean the planet spins fast enough to generate its own centrifugal force, then I don't see how you could manage to keep it tidally locked without the spinning axis I describe. $\endgroup$
    – Halfthawed
    Jun 10 at 3:44
  • $\begingroup$ @Zoey: If I understand you correctly, essentially you are saying that the "planet" extends over the entire orbit of the Earth, with the Sun in the center. Unfortunately, this configuration is grossly unstable. You need some sort of fantastic engines to maintain stability. If you have such engines, this means that the structure is engineered and under active control; in which case, the climate would also be under active control, most likely; why would the engineers solve the greater problem and leave the lesser one unsolved? $\endgroup$
    – AlexP
    Jun 10 at 10:46
  • $\begingroup$ The planet is held stable because magic. Gravity if from the rotation. I was just seeing if the distance would have made it safer. But guess not, would also have to find an in-world reason for it being the right temperature instead of a scientific one. $\endgroup$
    – Zoey
    Jun 10 at 23:36
  • $\begingroup$ @Halfthawed As I said before, I worded myself wrong. I just mean that the inner torus always faces the inside, like one would expect. You are putting way too much thought into my exact wording, even though I explained what I meant. $\endgroup$
    – Zoey
    Jun 10 at 23:39
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Yes, when it comes to a tidally-locked planet, it should be quite hot on the side facing the sun. Although when it is 1 AU away, it cannot be told whether the planet is even habitable in the first place, due to a lack of information of the parent star, e.g. radius, temperature etc. In usual conditions, like this question, the one side of the planet is extremely hot, while the other side is extremely cold. There should be a small area between these two regions which is habitable for animals to live in.

On estimating that the parent star is similar to our sun, then it should be extremely hot on the side facing the sun, even having the possibility of having "molten" areas due to the planet having no seasons at all.

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