5:15 PM - 7:15 PM
[PPS06-P14] Experimental study on impact fragmentation of icy planetesimals with thermally evolved internal structures
Asteroids are remnants of planetesimals during the planet formation process, and they still retain records of the planet formation process. So understanding the origin of asteroids is an important research object to reveal the planet formation process. Asteroid Ryugu is a particularly suitable asteroid for the research because there are a relatively large number of observational evidences that can be used to discuss its formation and origin due to the results of the Hayabusa2 mission. Since Ryugu is likely to be a rubble pile structure formed by the re-accumulation of impact fragments from its parent body and rich in water-containing clay minerals, its parent body is considered to as a layered icy planetesimals that experienced thermal evolution due to potential heat sources and has a chemically evolved interior. It is very interesting to clarify how the parent body experienced impact disruption and re-accumulation that led to the formation of a rubble pile body such as Ryugu, to approach the origin of asteroids.
In this study, we simulated thermally evolved bodies with a layered structure and prepared a target and conducted impact experiments. The target sample was a 6-cm-diameter layered sphere with a 1.5-cm-thick snow mantle with 40% porosity and a 3-cm-diameter mixed clay sphere composed of montmorillonite powder and silicon oil in the core. A two-stage light gas gun at Kobe University and ISAS was used in these impact experiments. Impact velocities ranged from 1 to 6 km/s. Three types of projectiles with diameters of 1.9 mm, 4.7 mm, and 7 mm were used. All experiments were observed by high-speed cameras, and in addition, the inside of the target was also observed by flash X-ray photography in the ISAS experiments.
In a previous study, the results of impact experiments on layered targets revealed four types of disruption modes determined by specific energy and the ratio of core mass to total target mass, which provide important clues for confirming the fragmentation mode of layered targets. In this study, we evaluated the fragmentation mode of layered targets with these four disruption modes. The relationship between the specific energy and the largest fragment mass was also examined.
The experimental results showed that the degree of disruption increased with the increase of the specific energy for all projectile sizes. However, for the projectile size of 1.9mm, the mantle catastrophically disrupted, and the core was intact at Q=898J/kg, but for the projectile size of 4.7mm, the core remnant with a crater on the surface was observed in addition to catastrophic disruption of the mantle at Q=294J/kg. Also, catastrophic disruption of the core was observed even at Q=16455J/kg for the projectile size of 4.7mm, while catastrophic disruption of the core was clearly observed at Q=6634J/kg for the projectile size of 7mm. These results imply that the specific energy alone is insufficient to discuss the target disruption mode, and at the same time projectile size has an effect on impact disruption. Similarly, the relationship between the specific energy and the largest fragment mass tended to suggest an effect of different projectile sizes.
[1] Okamoto and Arakawa.,2008, Experimental study on the impact fragmentation of core-mantle bodies: Implications for collisional disruption of rocky planetesimals with sintered core covered with porous mantle, Icarus 197 (2008) 627-637
In this study, we simulated thermally evolved bodies with a layered structure and prepared a target and conducted impact experiments. The target sample was a 6-cm-diameter layered sphere with a 1.5-cm-thick snow mantle with 40% porosity and a 3-cm-diameter mixed clay sphere composed of montmorillonite powder and silicon oil in the core. A two-stage light gas gun at Kobe University and ISAS was used in these impact experiments. Impact velocities ranged from 1 to 6 km/s. Three types of projectiles with diameters of 1.9 mm, 4.7 mm, and 7 mm were used. All experiments were observed by high-speed cameras, and in addition, the inside of the target was also observed by flash X-ray photography in the ISAS experiments.
In a previous study, the results of impact experiments on layered targets revealed four types of disruption modes determined by specific energy and the ratio of core mass to total target mass, which provide important clues for confirming the fragmentation mode of layered targets. In this study, we evaluated the fragmentation mode of layered targets with these four disruption modes. The relationship between the specific energy and the largest fragment mass was also examined.
The experimental results showed that the degree of disruption increased with the increase of the specific energy for all projectile sizes. However, for the projectile size of 1.9mm, the mantle catastrophically disrupted, and the core was intact at Q=898J/kg, but for the projectile size of 4.7mm, the core remnant with a crater on the surface was observed in addition to catastrophic disruption of the mantle at Q=294J/kg. Also, catastrophic disruption of the core was observed even at Q=16455J/kg for the projectile size of 4.7mm, while catastrophic disruption of the core was clearly observed at Q=6634J/kg for the projectile size of 7mm. These results imply that the specific energy alone is insufficient to discuss the target disruption mode, and at the same time projectile size has an effect on impact disruption. Similarly, the relationship between the specific energy and the largest fragment mass tended to suggest an effect of different projectile sizes.
[1] Okamoto and Arakawa.,2008, Experimental study on the impact fragmentation of core-mantle bodies: Implications for collisional disruption of rocky planetesimals with sintered core covered with porous mantle, Icarus 197 (2008) 627-637