Commensurability is the property of two orbiting objects, such as planets, satellites, or asteroids, whose orbital periods are in a rational proportion.
Examples include the 2:3 commensurability between the orbital periods of Neptune and Pluto,[1] the 3:4 commensurability between the orbital periods of the Saturnian satellites Titan and Hyperion,[2] the orbital periods associated with the Kirkwood gaps in the asteroid belt relative to that of Jupiter,[3] and the 2:1 commensurability between Gliese 876 b and Gliese 876 c.
Commensurabilities are normally the result of an orbital resonance, rather than being due to coincidence.
See also
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