5:15 PM - 7:15 PM
[PPS06-P18] Experimental study on the remnants of the impactor and their mixing on the crater floor during high-velocity impacts on small bodies
Keywords:crater formation, impactor, remnant, mixing
Background The surface layers of airless solid bodies, such as the Moon and asteroids, are covered with impact craters, formed through collisions with asteroids and comets. These impacts excavate the target body's surface, incorporating and mixing impactor material. This process, known as regolith gardening, has been studied through lunar samples and chondrite meteorites, where breccia formation has been observed. Asteroid Ryugu is classified as a C-type asteroid; however, exploration has revealed boulders that may have originated from S-type asteroids [1]. This suggests that regolith gardening plays a crucial role in its impact history. To understand impact evolution on asteroids, evaluating the survivability of impactor materials is essential.
Previous studies have focused primarily on target body impact strength, while impactor fracture behavior remains less studied. A prior study [2] demonstrated that impactor fragmentation characteristics vary with target type and impact conditions. That study used rock projectiles, providing key data for understanding S-type asteroid collisions. To further investigate regolith gardening processes involving comets and C-type asteroids, we conducted laboratory impact experiments using organic-rich and low-strength projectiles simulating such bodies. We analyzed projectile survivability and mixing within the regolith layer, contributing to a deeper understanding of impact-driven surface evolution.
Materials & Methods Impact experiments were conducted using a vertical single-stage light gas gun at Kobe University. Projectiles impacted targets at velocities ranging from 67 m/s to 209 m/s. Cylindrical projectiles, 10 mm in diameter and height, were prepared from quartz sand and plaster mixtures in 20:1, 15:1, and 10:1 ratios, as well as paraffin. Three target materials were used: diorite, quartz sand (500 μm grain size), and glass beads (10 mm diameter). Impact events were recorded at 5000 fps using two high-speed cameras to analyze projectile fragmentation and mixing. Additionally, post-impact fragments were collected and measured to examine differences in fragment size distribution and impact strength across target types.
Results & Discussion When paraffin projectiles impacted the diorite target, responses varied with velocity: some were completely fragmented, while others deformed. In contrast, impacts on quartz sand caused projectile deformation without fragmentation, whereas glass bead impacts resulted in projectile destruction. The fragmentation patterns observed in diorite and glass bead targets exhibited distinct size distribution characteristics. Although impact strength remained consistent, fragment size-frequency distributions differed between target types.For the quartz sand target, where only projectile deformation occurred, deformation increased linearly with kinetic energy, attributed to increased impact pressure. Additionally, crater rim diameter increased with kinetic energy, closely following the established scaling law for quartz sand (500 μm) [3].
When weak-strength projectiles (0.12 MPa), composed of quartz sand and gypsum, impacted quartz sand, fragmentation was observed at all velocities. Fragment size and dispersion varied with impact velocity.
Based on these findings, further analysis will focus on impactor material residuals and their mixing processes within the regolith layer.
[1] Tatsumi, E. et al. (2021). Nature Astronomy, 5(1), 39-45
[2] Nagaoka et al. (2014). Meteoritics & Planetary Science 49, Nr 1, 69–79
[3] Tsujido et al. (2015). Icarus 262, 79-92
Previous studies have focused primarily on target body impact strength, while impactor fracture behavior remains less studied. A prior study [2] demonstrated that impactor fragmentation characteristics vary with target type and impact conditions. That study used rock projectiles, providing key data for understanding S-type asteroid collisions. To further investigate regolith gardening processes involving comets and C-type asteroids, we conducted laboratory impact experiments using organic-rich and low-strength projectiles simulating such bodies. We analyzed projectile survivability and mixing within the regolith layer, contributing to a deeper understanding of impact-driven surface evolution.
Materials & Methods Impact experiments were conducted using a vertical single-stage light gas gun at Kobe University. Projectiles impacted targets at velocities ranging from 67 m/s to 209 m/s. Cylindrical projectiles, 10 mm in diameter and height, were prepared from quartz sand and plaster mixtures in 20:1, 15:1, and 10:1 ratios, as well as paraffin. Three target materials were used: diorite, quartz sand (500 μm grain size), and glass beads (10 mm diameter). Impact events were recorded at 5000 fps using two high-speed cameras to analyze projectile fragmentation and mixing. Additionally, post-impact fragments were collected and measured to examine differences in fragment size distribution and impact strength across target types.
Results & Discussion When paraffin projectiles impacted the diorite target, responses varied with velocity: some were completely fragmented, while others deformed. In contrast, impacts on quartz sand caused projectile deformation without fragmentation, whereas glass bead impacts resulted in projectile destruction. The fragmentation patterns observed in diorite and glass bead targets exhibited distinct size distribution characteristics. Although impact strength remained consistent, fragment size-frequency distributions differed between target types.For the quartz sand target, where only projectile deformation occurred, deformation increased linearly with kinetic energy, attributed to increased impact pressure. Additionally, crater rim diameter increased with kinetic energy, closely following the established scaling law for quartz sand (500 μm) [3].
When weak-strength projectiles (0.12 MPa), composed of quartz sand and gypsum, impacted quartz sand, fragmentation was observed at all velocities. Fragment size and dispersion varied with impact velocity.
Based on these findings, further analysis will focus on impactor material residuals and their mixing processes within the regolith layer.
[1] Tatsumi, E. et al. (2021). Nature Astronomy, 5(1), 39-45
[2] Nagaoka et al. (2014). Meteoritics & Planetary Science 49, Nr 1, 69–79
[3] Tsujido et al. (2015). Icarus 262, 79-92