Wikipedia: Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of Jupiter <https://en.wikipedia.org/wiki/Jupiter>'s moons Ganymede <https://en.wikipedia.org/wiki/Ganymede_(moon)>, Europa <https://en.wikipedia.org/wiki/Europa_(moon)> and Io <https://en.wikipedia.org/wiki/Io_(moon)>, and the 2:3 resonance between Pluto <https://en.wikipedia.org/wiki/Pluto> and Neptune <https://en.wikipedia.org/wiki/Neptune>. In[234]:= MinorPlanetData["Pluto"][EntityProperty["MinorPlanet", "OrbitPeriod"]] Out[234]= Quantity[247.92065, "JulianYears"] In[235]:= PlanetData["Neptune"][EntityProperty["Planet", "OrbitPeriod"]] Out[235]= Quantity[164.79132, "JulianYears"] In[236]:= ContinuedFraction[%%/%] Out[236]= {1, 1, 1, 55, 1, 1, 1, 7} That's a fairly lousy approximation to 2:3. What's going on? —rwg