When the planets were first forming, they were orbiting within a disc of gas, and while inside that disc, they can actually slide around and adjust their orbits to their neighbors until they're perfectly in tune.
Cuando los planetas se formaron, orbitaban dentro de un disco de gas, y mientras estaban dentro de ese disco, de hecho, pueden deslizarse y ajustar sus órbitas  con las de sus vecinos hasta estar en perfecta sintonía.