Science. 1964 Sep 18;145(3638):1302-3. doi: 10.1126/science.145.3638.1302.
Numerical integration of the orbits of the five outer planets over 120,000 years reveals that the distance between Pluto and Neptune at the closest approaches oscillates within a narrow range. The distance is never much less than the aphelion distance of Pluto from the orbit of Neptune. The near commensurability in the periods of Pluto and Neptune and the eccentricity of Pluto's orbit are responsible for the libratory motion.
对五颗外行星轨道进行 12 万多年的数值积分表明，冥王星和海王星在最接近时的距离在一个狭窄的范围内波动。这个距离从未小于冥王星远日点到海王星轨道的距离。冥王星和海王星周期的近谐和以及冥王星轨道的偏心率是造成这种摆动运动的原因。
