Question re binary star systems & possible orbits

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Discussion Overview

The discussion revolves around the orbital dynamics of planets in binary star systems, specifically exploring the types of binary systems (S-type, P-type, T-type) and the implications for planetary orbits, visibility of stars, and potential daily phenomena such as "pre-sunrise" and "post-sunset" due to the presence of a dimmer star. The conversation includes theoretical considerations and speculative scenarios regarding orbital stability and resonance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants describe S-type and P-type planets, noting that S-type planets experience oppositions and superior conjunctions approximately once a year, while P-type planets experience superior and inferior conjunctions twice in their orbital period.
  • There is a suggestion that a planet could experience daily "pre-sunrise" and "post-sunset" if located at the L5 trojan point of a dimmer star in a T-type system.
  • Concerns are raised about the stability of T-type systems due to mass ratio requirements for Lagrange point stability.
  • One participant questions the implications of retrograde rotation on the planet's visibility of the stars, proposing scenarios involving tidal locking and resonance with the stars.
  • Another participant expresses interest in the theoretical possibilities and mentions using the concepts in a sci-fi novel.
  • There is a discussion about the potential for a planet to lock into a 2:1 resonance, with questions about the nature of the locking (to planet orbit or star orbit).

Areas of Agreement / Disagreement

Participants express varying viewpoints on the feasibility of different orbital scenarios and the implications of retrograde rotation. There is no consensus on the stability of T-type systems or the specifics of resonance locking.

Contextual Notes

Participants mention limitations related to the mass ratio for stability in T-type systems and the complexities of resonance conditions, but these aspects remain unresolved.

Who May Find This Useful

Readers interested in astrophysics, orbital mechanics, and speculative scenarios involving binary star systems may find this discussion relevant.

Kate_C
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TL;DR
Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star?
From what I gather, there are S-type, P-type & T-type systems, but I'm having a hard time wrapping my mind around the orbital possibilities. Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star? And could there be daily syzygy with the stars or might it need to be less frequent? If anyone can advise, it would be so appreciated! Thank you!
 
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For a S-type planet, the second star orbits like a superior planet. It therefore has oppositions and superior conjunctions - both of them approximately once a year.
For a P-type planet, the second star orbits like an inferior planet. It therefore has superior and inferior conjunction - total of approximately twice in its own orbital period. Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.
 
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Kate_C said:
Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star?

Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).
 
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T-type is problematic, though, due to the mass ratio requirements of Lagrange point stability.
 
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snorkack said:
For a S-type planet, the second star orbits like a superior planet. It therefore has oppositions and superior conjunctions - both of them approximately once a year.
For a P-type planet, the second star orbits like an inferior planet. It therefore has superior and inferior conjunction - total of approximately twice in its own orbital period. Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.
Thank you for clarifying! Very helpful!
 
DrStupid said:
Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).
Great to know! Thank you SO MUCH for your help with this and for the expertise!
 
Last edited:
DrStupid said:
Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).
So, if I'm understanding correctly, that would make for a post-sunset in this case by the dimmer star?
 
Kate_C said:
So, if I'm understanding correctly, that would make for a post-sunset in this case by the dimmer star?
Both L4 and L5 are equally stable, or not, depending on the mass ratio of primary and secondary.
Elongation to primary star is 60 degrees each case. Whether it is evenstar or morningstar depends on the rotation axis of tertiary.
 
Thank you!
 
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snorkack said:
...Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.

What if the planet has retrograde rotation? Assume it is close enough to tidal lock with one of the red dwarfs if the dwarf was non-binary. The heavy side of the planet that would otherwise face the star would see the smaller dwarf at sunrise, the stars would eclipse or pass close together (conjunction) at noon (if at zero longitude), and then at sunset the smaller dwarf would still be up later. Why would it slow rotation below 1:1 resonance?

Is there any reason it could not lock into a 2:1 resonance?
 
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Thank you for weighing, stefan r! I viewed some simulations that appeared to illustrate this and proceeded to write a sci-fi novel around the premise. I'm very glad to know it sounds within the realm of possibility.
 
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stefan r said:
What if the planet has retrograde rotation? Assume it is close enough to tidal lock with one of the red dwarfs if the dwarf was non-binary. The heavy side of the planet that would otherwise face the star would see the smaller dwarf at sunrise, the stars would eclipse or pass close together (conjunction) at noon (if at zero longitude), and then at sunset the smaller dwarf would still be up later. Why would it slow rotation below 1:1 resonance?

Is there any reason it could not lock into a 2:1 resonance?
What do you mean - lock of planet rotation to planet orbit, or to star orbit?
 

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