Momentum transfer in hypervelocity cratering of meteorites and meteorite analogs: Implications for orbital evolution and kinetic impact deflection of asteroids

George J. Flynn, Daniel D. Durda, Mason J. Molesky, Brian A. May, Spenser N. Congram, Colleen L. Loftus, Jacob R. Reagan, Melissa M. Strait, Robert J. Macke

International Journal of Impact Engineering
Volume 136, February 2020, 103437



• Ejecta from hypervelocity impact cratering results in significant momentum transfer, equaling or exceeding the direct momentum transfer from the projectile.
• The momentum transfer from hypervelocity cratering decreases with increasing target porosity.
• Impact cratering of hydrous targets produces greater momentum transfer than for anhydrous targets of the same porosity, likely resulting from the vaporization of water.”

“Kinetic impact is regarded as an effective way to divert an asteroid on a collision course with the Earth. However, asteroids show a wide diversity in their mineralogy, porosity, and water content, all of which are expected to influence their response to hypervelocity impact. Asteroids range in composition from primitive undifferentiated objects to differentiated objects. Among the undifferentiated asteroids they range from more reflective, carbon-poor bodies to darker, carbonaceous bodies. Porosities of asteroids range from 0 to >50%, with most >20%, and some asteroids exhibit a 0.7 µm water feature in their reflection spectra. Mineralogy, porosity and hydration are each expected to influence the momentum transferred in hypervelocity collisions. We conducted a series of measurements of the post-impact momentum, which is characterized by a factor β, the ratio of the total linear momentum acquired by the target to the momentum of the impactor. We measured β for anhydrous meteorites, which sample their asteroidal parent bodies, spanning a wide range of porosities: including 7 samples of the CV3 carbonaceous chondrite Northwest Africa (NWA) 4502 (2.1% porosity), 7 samples of the ordinary chondrite NWA 869 (6.4% porosity), 4 samples of the ordinary chondrite Saratov (15.6% porosity), and, to extend our measurements to higher porosity than is found among meteorites, 2 samples of terrestrial pumice (80% porosity). We also measured β for hydrous meteorite analog targets: including 2 samples of terrestrial serpentine (17.9% porosity) and 4 samples of terrestrial montmorillonite (51.5% porosity), the two clay minerals that dominate the composition of the hydrous CI carbonaceous chondrite meteorites, as well as 4 samples of hydrous meteorite analog material prepared by powdering and hydrating an anhydrous carbonaceous chondrite. We found that for both the anhydrous and the hydrous samples β decreased with increasing porosity, consistent with hydrocode modeling. However, the β values we measured for the ∼5 km/s impacts onto these anhydrous samples, with β = 3.55 for NWA 4502, 2.69 for NWA 869, 2.10 for Saratov, and 2.15 for pumice, are larger than results from hydrocode modeling for 10 km/s impacts into relatively strong, porous rock targets. The β values for the moderate porosity (17.9%) hydrous serpentine targets (β = 4.70), the highly porous (51.55%) hydrous montmorillonite targets (β = 2.79), and the moderately porous CI-analog targets (β = 2.99) are each significantly larger than the β value for anhydrous targets of comparable porosities. This is likely due to jetting of water vapor, which could significantly affect the deflection of hydrous asteroids and icy comets in natural or human-induced collisions.”