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How do gravitational resonances with Jupiter move asteroids into Earth-crossing orbits?

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asteroid Ida and its satellite, Dactyl — Small body Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.

Gravitational resonances with Jupiter influence the orbits of asteroids through a process involving Kirkwood gaps and orbital perturbations.12

When an asteroid’s orbital period is a simple fraction of Jupiter’s, it enters a mean-motion resonance. In these regions, the asteroid experiences repeated gravitational tugs from Jupiter in a fixed direction at regular intervals. These perturbations can destabilize the asteroid's orbit, eventually clearing these zones of material—creating the gaps observed in the main belt.12

Small asteroids often enter these resonance zones following collisions with other bodies or through the Yarkovsky effect, a force caused by the emission of thermal radiation that allows smaller objects to drift. Once an asteroid is within or near these resonances, Jupiter’s gravitational influence continues to perturb its orbit, causing the asteroid's eccentricity to increase. This evolution pushes the object into an Earth-crossing orbit, where it may eventually collide with Earth or be ejected from the solar system.23