The Belt Records One Catastrophe

01The evidence

• Dynamical models of the inner asteroid belt trace its evolution through collisions and transport, and the resulting size-frequency distributions carry structure that a steady cascade does not naturally produce.Dynamical evolution of the inner asteroid belt
• Dynamical constraints on the evolution of the belt and the sources of meteorites link specific families to specific meteorite classes, which makes family ages a measurable input rather than a fitted one.Cambridge, IAU proceedings

02The tension

Collisional cascades predict a size distribution that is smooth and close to a power law. The belt has a knee, and the standard explanation is a change in the dominant disruption physics at a threshold size. That explains a bend but not the fine structure, and it requires tuning.

03The theory

A single large disruption at a particular time injects a characteristic spectrum of fragments. The largest fragments remain as a family, the smallest diffuse, and the intermediate sizes carry the imprint of the event's energy partition.

If that one event dominates the inventory of a size range, then the distribution in that range is not a steady state. It is a snapshot of a decaying family, and it should show a sharp edge at the largest fragment and a characteristic slope set by the fragmentation law rather than by the cascade.

The test is ages. Families associated with the knee should share an age within a narrow window, and that window should coincide with an independent event marker, such as a spike in meteorite ages or a specific dynamical resonance crossing.

This would also mean the belt is not in collisional equilibrium, which matters for every model that uses its current size distribution to infer the bombardment history of the inner solar system.

04What this is not

05Predictions

• P1Families associated with the knee in the size distribution should share a common age within a narrow window.
• P2The slope of the distribution near the knee should match a fragmentation law rather than a cascade equilibrium.
• P3Meteorite classes linked to those families should show an age cluster at the same time.

06What would refute it

Family ages that are smoothly distributed across hundreds of millions of years would restore the cascade and remove the single-event explanation.

07What it would change

It would rewrite bombardment histories and change how the belt is used to date surfaces in the inner solar system.