The Pluto Files: The Rise and Fall of America's Favorite Planet

by Neil deGrasse Tyson

perturbing Uranus.

Although Pluto’s orbit crosses that of Neptune, they will never collide because Neptune has Pluto in another kind of lock, called an orbital resonance. For every three trips around the Sun that Neptune takes, Pluto takes exactly two, leaving them in an eternal three-to-two resonance with each other. No other pair of planets behaves this way.