Low Speed Granular–Granular Impact Crater Opening Mechanism in 2D Experiments

Quasi-2D, low-velocity experiments of colliding granular projectiles against granular targets were performed by means of a 7 m-long Hele-Shaw cell. The processes involved in the crater-opening mechanism of low-velocity granular-against-granular collisions are described. We show that the crater is opened mainly by a compaction process of the target. The projectile is fragmented and its lower section suffers a severe compaction; this projectile remnant forms a central dome or peak inside the crater. When the target reaches its maximum degree of compaction, the excess of momentum generates fast avalanches sliding on the slopes of the confined material, and exerts pressure on the crater walls, increasing its diameter. We propose that low-velocity collisions between granular aggregates are a possible mechanism that allows the growth of small planetary objects or the aggregation after catastrophic or high-energy collisions.