Between Mars and Jupiter lies the main asteroid belt: hundreds of thousands of rocky bodies whose orbits are sculpted by Jupiter's immense gravity. This interactive simulation shows thousands of asteroids and the empty Kirkwood gaps that Jupiter's orbital resonances carve into the belt.
Asteroids whose orbital period forms a simple ratio with Jupiter's (such as 3:1, 5:2 or 2:1) receive repeated gravitational kicks at the same point in every orbit. Over millions of years these kicks pump up their eccentricity until they are ejected from the resonance, leaving behind the near-empty Kirkwood gaps first identified by Daniel Kirkwood in 1866.
Drag to pan and scroll to zoom. Adjust asteroid count to thicken or thin the belt, increase Jupiter's influence to widen and deepen the gaps, and toggle resonance lines to see exactly where the 3:1, 5:2 and 2:1 gaps sit relative to Jupiter's orbit.
Despite containing over a million known objects, the asteroid belt's total mass is only about 3% of the Moon's — it is far too sparse for spacecraft to worry about collisions when passing through, contrary to popular depictions in film.
This asteroid belt simulation models the main belt between Mars (1.52 AU) and Jupiter (5.2 AU) as thousands of individual bodies orbiting the Sun. Asteroid density is deliberately thinned near specific orbital radii that correspond to mean-motion resonances with Jupiter — the 3:1, 5:2 and 2:1 Kirkwood gaps — reproducing the characteristic clumpy structure of the real belt, first mapped by Daniel Kirkwood in the 1860s.
Jupiter's gravity resonates with asteroids whose orbital period is a simple fraction of its own (11.86-year) period. Repeated gravitational tugs at the same orbital phase pump up eccentricity over time, clearing these radii of stable, near-circular asteroids and creating the observed gaps in the belt's radial distribution.
Drag to pan, scroll or use the Zoom slider to zoom. Asteroid count controls the total population, Jupiter influence widens and deepens the Kirkwood gaps, Simulation speed scales orbital motion, and the resonance-line toggle marks exactly where the 3:1, 5:2 and 2:1 gaps fall.
Not every resonance clears a gap — the Hilda asteroids sit stably in Jupiter's 3:2 resonance (the same type that protects Pluto from Neptune), showing that resonances can either destabilise or stabilise an orbit depending on its geometry.
Kirkwood gaps are radii within the asteroid belt where very few asteroids are found, caused by orbital resonances with Jupiter. Astronomer Daniel Kirkwood first identified them in 1866 while studying the distribution of known asteroid orbits, correctly attributing them to Jupiter's gravitational influence decades before computers could confirm the mechanism numerically.
At a resonance such as 3:1, an asteroid passes close to Jupiter at the same orbital phase every three orbits, receiving a repeated gravitational nudge in the same direction. Over many cycles this steadily increases the asteroid's orbital eccentricity until it crosses the orbit of Mars or another planet, is scattered away, or falls into the Sun, emptying that radius of stable bodies.
Despite containing well over a million cataloged objects, the entire asteroid belt has a combined mass of only about 3 x 10^21 kg, roughly 3% of the Moon's mass — with nearly half of that concentrated in the single largest body, the dwarf planet Ceres.
The risk is extremely low. Even with a million-plus known asteroids, the belt spans a volume so vast that the average distance between objects is millions of kilometres. Every spacecraft sent through the belt, including Pioneer, Voyager, Galileo, New Horizons and Juno, has passed through without incident.
The main belt is the general population of asteroids between Mars and Jupiter. Within it, most Kirkwood gap radii are depleted, but certain resonances — like the 3:2 resonance occupied by the Hilda family and the 1:1 resonance occupied by Jupiter's Trojan asteroids — are stable and host their own asteroid populations rather than being emptied out.