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Can a Moon Alternately Orbit Two Planets?

-- Nox | July 9, 2022

Question:

Hi! I’m writing a novel and I was wondering if you had any insight on the topic. I want to know if the following situation can happen, and how it would work. If you don’t know how it can happen but have theories I would love to hear them!

Two moons (moon A and moon B) orbit planet A, sometime throughout the year moon B begins to orbit planet B. Then after some time in orbit moon B goes back and orbits planet A for some time. This cycle repeats every so often.

I’m leaving time periods open because I have no idea what time period would be realistic.
Thank you for your time! -Nox

-- Nox

Answer:

I don’t believe that the scenario you describe, were a moon is effectively shared by two planets in a two-planet and two-moon configuration, would be stable. A more stable situation would be for the moons to orbit the common gravitational center, or barycenter, of a two-planet system where the planets orbit each other in a very close configuration. This would not be the same, though, as the configuration you propose.

-- Jeff Mangum

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