Hypervelocity Impact of Three L-Type Ordinary Chondrites: A Test of the Variation of β and Q*D with Target Porosity and Strength

Abstract Response to hypervelocity impact influences the morphology and size of craters, the orbital change from collisions, fragmentation in disruptive collisions, and the size-frequency and speed distributions of the dust produced. Successful deflection of a hazardous asteroid by kinetic impact requires cratering without disruption in order to avoid leaving a large fragment on a collision course. To investigate the maximum velocity that can be transferred by a single kinetic impact, we performed a series of hypervelocity impact cratering and disruption measurements on three types of anhydrous asteroid samples: Aba Panu, Northwest Africa 869 (NWA 869), and Saratov. These three L-type ordinary chondrite (OC) meteorites, with the same mineralogy and low degrees of weathering and shock, span most of the porosity and strength ranges of OCs. The speed-of-sound, unconfined compressive strength, and dynamic Young’s modulus each decreased with increasing sample porosity as expected from modeling and the properties of terrestrial rocks. The momentum enhancement factor, β – 1, in ~5 km/s impacts also decreased with increasing porosity, with β = 3.7 for Aba Panu (porosity 3.1%), β = 2.5 for NWA 869 (porosity 6.4%), and β = 2.3 for Saratov (porosity 14.1%). Higher porosity targets were expected to be more resistant to disruption based on modeling and experiments on terrestrial rocks. However, the energy for the onset of catastrophic disruption, Q*D, peaked for the intermediate porosity for these samples: Q*D = 1,148 J/kg for Aba Panu, 1,795 J/kg for NWA 869, and 1,070 J/kg for Saratov. Cosmic ray exposure ages, which are sensitive to the resistance to breakup, show the same trend for L-chondrites, with both low- and high-porosity meteoroids having shorter mean exposure ages than those of intermediate porosity. This suggests the behavior of meter-scale meteoroids can be inferred from experiments on the cm-scale.