Hypervelocity impact occurs when a cosmic projectile is large enough (typically >50 m for a stony object and >20 m for an iron body) to pass through the atmosphere on Earth with little or no deceleration and so strike at virtually its original cosmic velocity (>11 km s⁻¹; French, 1998). This produces high-pressure shock waves in the target. Smaller projectiles lose most of their original kinetic energy in the atmosphere and produce small metre-size ‘penetration craters’, without the production of shock waves.