5:15 PM - 6:45 PM
[PPS07-P13] Experimental study on re-accumulation processes of iron-rock rubble-pile bodies
Keywords:rubble-pile, M-typ asteroid
Many asteroids are known to exist in the solar system, and it is believed that they have kept the original state of the solar system in the early stage of its formation. Therefore, the impact and reaccumulation processes experienced by asteroids are very important information for elucidating the formation and evolution of solar-system celestial bodies. Asteroids are considered to have a rubble pile structure in the initial stage of growth by impact destruction and reaccumulation of celestial bodies. The study of impact and collapse phenomena of rubble pile asteroids is a key to understand the formation process of the solar system. Asteroids are classified into several types based on their compositional materials, but there are few M-type asteroids, which are thought to be formed by impact debris or reaccumulated impact debris from planetesimal that were differentiated into two layers, rock and molten metal cores. In previous studies, impact destruction experiments have been performed on simulated rock rubble pile objects consisting of glass beads, and the energy distribution efficiency from impact energy to kinetic energy in non-destructive beads is found to be about 1 to 3%. However, there have not been many studies using simulated metal rubble pile objects. In this study, we performed impact destruction experiments on a target sample simulating an iron rubble pile object and focused on the difference in the behavior of impact debris due to the difference in the tensile strength of the adhesive on the target sample. We also performed collisional fracture experiments on a target sample with the same adhesive strength, but with different particle compositions.
To simulate a rubble pile object on a laboratory scale, iron balls and glass beads with a diameter of 6 mm were used as the target particles. Gypsum, Aron Alpha, and Cemedine were used as adhesives. The target particles were double-thrusted to ensure maximum density. Three types of target sample sizes were prepared with 109, 63, and 32 constituent particles, respectively. Impact experiments were conducted using a vertical one-stage light gas gun at Kobe University. The target was set in a vacuum chamber and evacuated below 1000 Pa. Nylon balls with a diameter of 10 mm were used as bullets, and the impact velocity vi was in the range of 90 to180 m/s.In the analysis, camera calibration was used to obtain three-dimensional debris particle velocity data, and a high-speed camera was used to capture images of the experiment.
Although the kinetic energy efficiency varied slightly depending on the strength of the adhesive, it was slightly less than 20% for glass beads and around 10% for iron. This result is larger than that of 1% for basalt, which was shown in a previous study. The fragment particles of targets with a rubble pile structure, which do not inherently have a bonding force between rock masses, do not require energy to break the bond, indicating that the kinetic energy of the bullet is efficiently transferred to the fragment particles. The median velocity (the velocity of fragments when the accumulated mass of fragments becomes half of the original target mass when the fragments are arranged from the fastest to the slowest, a value described by the impact disruption strength and empirical equation) is larger for the iron-rubble pile target than for the frozen clay target and the porous gypsum target. This suggests that the debris velocity of iron-rubble pile targets is larger than that of other targets after impact failure. The collisional fracture strength of iron-rubble pile targets is smaller than that of frozen clay and porous gypsum targets. The collisional fracture strength is a characteristic of the ease of breakage of a material, and this result suggests that iron-rubble pile targets may be more easily broken and less likely to reaccumulate than other materials.
To simulate a rubble pile object on a laboratory scale, iron balls and glass beads with a diameter of 6 mm were used as the target particles. Gypsum, Aron Alpha, and Cemedine were used as adhesives. The target particles were double-thrusted to ensure maximum density. Three types of target sample sizes were prepared with 109, 63, and 32 constituent particles, respectively. Impact experiments were conducted using a vertical one-stage light gas gun at Kobe University. The target was set in a vacuum chamber and evacuated below 1000 Pa. Nylon balls with a diameter of 10 mm were used as bullets, and the impact velocity vi was in the range of 90 to180 m/s.In the analysis, camera calibration was used to obtain three-dimensional debris particle velocity data, and a high-speed camera was used to capture images of the experiment.
Although the kinetic energy efficiency varied slightly depending on the strength of the adhesive, it was slightly less than 20% for glass beads and around 10% for iron. This result is larger than that of 1% for basalt, which was shown in a previous study. The fragment particles of targets with a rubble pile structure, which do not inherently have a bonding force between rock masses, do not require energy to break the bond, indicating that the kinetic energy of the bullet is efficiently transferred to the fragment particles. The median velocity (the velocity of fragments when the accumulated mass of fragments becomes half of the original target mass when the fragments are arranged from the fastest to the slowest, a value described by the impact disruption strength and empirical equation) is larger for the iron-rubble pile target than for the frozen clay target and the porous gypsum target. This suggests that the debris velocity of iron-rubble pile targets is larger than that of other targets after impact failure. The collisional fracture strength of iron-rubble pile targets is smaller than that of frozen clay and porous gypsum targets. The collisional fracture strength is a characteristic of the ease of breakage of a material, and this result suggests that iron-rubble pile targets may be more easily broken and less likely to reaccumulate than other materials.