Hypervelocity impact cratering of chondritic meteorites: Implications for asteroid recoil

Porosities of asteroids range from 0 to >50%, with most >20%. Meteorites, which sample asteroids, have a similar range. Since porous targets react differently to hypervelocity cratering than non-porous targets, it is critical to measure the response of asteroid samples to impacts. We impacted 5 samples of the CV3 carbonaceous chondrite Northwest Africa (NWA) 4502 with a mean porosity of 2.1%, 7 samples of the ordinary chondrite NWA 869 with a mean porosity of 6.4%, and 1 sample of the ordinary chondrite Saratov with a porosity of 15.6%. Each meteorite was impacted by a 1/16” Al-sphere shot at 4.34 to 5.89 km/s at the NASA Ames Vertical Gun. Using high-speed video images we measured the recoil speed of each target and determined the momentum multiplication factor (b), the ratio between the recoil momentum of the target and the momentum of the impactor. b decreased with increasing porosity, consistent with hydrocode modeling. However, the b values are larger, with b = 3.37 for NWA 4502, 2.70 for NWA 869, and 1.49 for Saratov, than results from hydrocode modeling for 5 km/s impacts into porous rock targets. Even the most porous meteorite we impacted had substantial momentum enhancement from crater ejecta. This should be considered in design of kinetic impact missions and modeling alteration of asteroid orbits by collisions.