Jupiter acts as a cosmic broom, sweeping the asteroid belt clean

Space · Published 18 October 2026 Swipe more like this →

In short: Why are there specific empty zones in our solar system's asteroid belt? These celestial voids, known as Kirkwood gaps, reveal how Jupiter’s gravity systematically dismantles the orbits of nearby space rocks, turning stable paths into chaotic trajectories that eventually eject them from their homes.

First identified by Daniel Kirkwood around 1860, these gaps appear as dips in the distribution of asteroid semi-major axes. They occur at specific locations where an asteroid's orbital period is a simple fraction of Jupiter's. For example, in the 3:1 resonance, an asteroid completes three orbits for every one orbit of Jupiter. These gravitational interactions are not subtle; an object in these zones is disturbed regularly by Jupiter's pull, causing its orbit to vary chaotically and evolve into a planet-crossing path within a few million years.

Because the ν5 and ν6 secular resonances intersect inside the mean-motion resonances, the depletion process becomes especially intense. While some resonances, like the 3:2 resonance with Neptune, can capture objects, most Kirkwood gaps are depleted. A notable exception is the 2:1 resonance, which contains relatively stable islands. However, even these are slowly losing members to diffusion, a process potentially accelerated in the past when Jupiter and Saturn were closer to a 5:2 resonance.

These gaps serve as a primary source for near-Earth asteroids. Collisions between main-belt asteroids near a gap can produce small fragments. These fragments are then nudged by the Yarkovsky effect—a force caused by the anisotropic emission of thermal radiation from the asteroid's surface. This allows them to drift into the Kirkwood gap, where Jupiter's perturbations eventually kick them into orbits that cross Earth's path, potentially leading to collisions or ejection from the solar system entirely.

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