If a habitable planet is in a hierarchical triple star system (not unlike alpha Centauri) and has two moons but has a large torrid zone, what characteristics would my moons need to have in terms of orbits, size and affects on tides for this to be able to support humanoid life? So far I've got an F-type star as the main star in the system and the one that the planet orbits while there is a M-Type star that also obits the F-type star. Quite a bit further out I planned a b-type star that orbits both of the other stars. I've picked an axial tilt for my planet of about 38 degrees. But everything is up for change as long as it leads to a planet that can support larger than normal humanoid beings and life in general and have a tropical equatorial climate.

  • $\begingroup$ I would suggest not accepting an answer for at least a day. There are some quite brilliant people on this stack who may come up with brilliant responses that show how the additional stars actually do need to be taken into account. $\endgroup$ Feb 17, 2023 at 21:00
  • $\begingroup$ I didn't understand initially since I'm new here that the check mark was acceptance and not just liking. $\endgroup$ Feb 17, 2023 at 21:44
  • $\begingroup$ No problem. You can click the "Up" arrow by any answer that you like and a "Down" arrow if you do not like it. The Up arrow will give that user +10 points, and the Down arrow will give that user -10 points. The down arrow does cost you points however (-2, I think). You may click the "Accept" checkmark on a single answer for each question, which will give that user +15 points. It is customary to wait at least 24 hours before Accepting an answer. $\endgroup$ Feb 17, 2023 at 22:09

1 Answer 1


The 2nd and 3rd stars can be mostly excluded from your planet-moons system calculations. The 3rd star is definitely out of the way, especially if it is close analog of the Alpha Centauri system. The 2nd star must be far enough away so that it's radiation (combined with the M-Type) doesn't bake the atmosphere away.

With both 'extra' stars that far away, just keep the moons well within the planet's Hill sphere and you only need to worry about how the moons and planet are interacting rather than what additional, external, bodies are doing.


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