Orbital resonance
A repeating gravitational nudge that happens when two bodies' orbital periods form a simple ratio, such as 2:1 or 3:2.
Imagine pushing a child on a swing. Small pushes timed to match the swing's rhythm build up into big movements. Orbital resonance works the same way. If one body goes round the Sun exactly three times for every one orbit of Jupiter, it meets Jupiter at the same points again and again, and the planet's small gravitational tugs keep adding up.
Resonances can either stabilise or destabilise. Pluto is protected by a 3:2 resonance with Neptune: it makes two orbits for every three of Neptune's, so the two never come close even though their paths appear to cross. Jupiter's moons Io, Europa and Ganymede are locked in a 1:2:4 chain. In the asteroid belt, by contrast, resonances with Jupiter tend to stretch orbits until asteroids are thrown out, carving the Kirkwood gaps.
For meteorite science this is the delivery mechanism. Fragments chipped off asteroids drift slowly until they fall into a resonance, which then pumps their orbits into paths that cross Earth's. Many meteorites, from ordinary chondrites to the pieces of Vesta known as HED meteorites, probably reached us this way. Resonances are found by calculating orbital periods, not by looking through a telescope.
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