Hypervelocity cratering and disruption of the Northwest Africa 4502 carbonaceous chondrite meteorite: Implications for crater production, catastrophic disruption, momentum transfer and dust production on asteroids

Abstract

The meteorites provide samples of their asteroidal parent bodies, allowing laboratory measurements of the response of asteroidal material to hypervelocity impacts. The meteorites span a wide range of physical properties, with porosities ranging from near zero to more than 40%, comparable to the range determined for stony asteroids. To investigate the effects of target properties on cratering, impact disruption, momentum transfer and dust production we have begun a series of hypervelocity impact experiments on various types of meteorite targets. In this work whole stones or fragments of the Northwest Africa 4502 (NWA 4502) CV3 carbonaceous chondrite were impacted by 1/16” or 1/8” Al-spheres at speeds ranging from 4.11 to 5.89 ​km/s at the NASA Ames Vertical Gun Range. These samples had a mean porosity of ~2.1% and a mean unconfined compressive strength of ~32.9 ​MPa. Eight hypervelocity disruptions demonstrated that these NWA 4502 targets are less resistant to disruption, i.e., they require less impactor kinetic energy per unit target mass to produce an equivalent disruption, than non-porous terrestrial basalt targets or ordinary chondrite meteorite targets. The threshold collisional specific energy, Q∗D, for these NWA 4502 targets is ~224 ​J/kg, which is significantly lower than the ~1795 ​J/kg value we measured previously for the moderately porous (~6.4%) ordinary chondrite meteorite Northwest Africa 869. This likely results from the numerous cracks crosscutting the NWA 4502 samples. We measured the post-impact momentum of seven NWA 4502 cratering events and found a mean momentum transfer of 3.55 times the momentum of the projectile, showing that the recoil from the crater ejecta significantly exceeded the direct momentum transferred by absorption of the projectile. In two cases we found much higher momentum transfer values (11.72 and 8.95), suggesting these two impactors struck a different material, likely hydrous weathering veins, which fill the cracks, than the other five NWA 4502 cratering impacts. This suggests that hydrous asteroids and comets would experience significantly more recoil from hypervelocity impact than anhydrous targets having similar strength and porosity.