Impact fragmentation of carbonaceous meteorites with pre-existing large cracks

Carbonaceous asteroids like Ryugu and Bennu have experienced the catastrophic disruption of their parent bodies and subsequent cratering impacts. Their internal structure resembles a rubble-pile, and some of their boulders have large cracks on their surfaces. Indeed, regolith grains sampled and returned to Earth were found to have numerous cracks, some of which extended through the entire interior of the samples. In an impact, pre-existing large cracks are likely to affect subsequent disruption and fragmentation. Hence, pre-existing large cracks affect the size distribution and lifetime of these boulders, - and thereby asteroids. However, it is unclear how exactly fracturing is influenced by pre-existing large cracks. The purpose of this study is to investigate how pre-existing large cracks influence the fragmentation of targets. We therefore conducted impact experiments on carbonaceous meteorites with and without internal cracks. A spherical alumina projectile with 1.0 mm and a glass projectile with 0.80 mm in diameter were fired into 1-2 cm-sized Allende (CV3), Murchison (CM2) and Aguas Zarcas (CM2) targets at nominal impact velocities of 2.0 and 4.0 km s−1, respectively. X-ray computer tomography imaging on the meteorite before impact and on the largest fragment after impact were performed. The experiments show that, for CV and CM meteorites, several of the newly exposed surfaces on the largest impact fragments were formed along pre-existing large cracks. Measurements of fragment size distributions from the disruption of CM meteorites revealed a deficiency of small fragments, potentially explaining the scarcity of fine particles on small carbonaceous asteroids.