Stability of the Solar System essentially the distance from sun to earth). These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but their orbits are unstable and they will eventually break out of the resonance due to close encounters with a major planet. Another common form of resonance in the Solar System is spin–orbit resonance, where the period of spin (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is our own Moon, which is in a 1:1 spin–orbit resonance
Planet Nine the disk had a distant inner edge, 100–200 AU, a planet encountering Neptune would have a 20% chance of being captured in an orbit similar to that proposed for Planet Nine. The observed clustering is more likely if the inner edge is at 200 AU. Unlike the gas nebula the planetesimal disk is likely to be long lived, potentially allowing a later capture. Planet Nine could have been captured from beyond the Solar System during a close encounter between the Sun and another star in its birth cluster. Three-body interactions during these encounters can perturb the path of planets on