11:00 AM - 11:15 AM
[PPS07-07] Exploring the bouncing conditions for dust aggregates with collision simulations
Keywords:dust aggregates, planetesimal formation
The formation of planetesimals in protoplanetary disks begins with the coagulation of dust aggregates. Millimeter-wave polarization observations have revealed the presence of high-density dust aggregates with filling factors exceeding 0.1 in protoplanetary disks (e.g., Tazaki et al. 2019). Such high-density dust aggregates are known to collide and exhibit bouncing, which is crucial to consider in the evolution of protoplanetary disks and planet formation.
The bouncing behavior of dust aggregates has been studied through laboratory experiments and numerical simulations, resulting in differing bouncing conditions. Laboratory experiments using silicate spheres have shown that the effective mass of aggregates for bouncing is proportional to the collision velocity raised to the power of -4/3 (Kothe et al. 2013). In contrast, numerical simulations using close-packed and particle-extraction(CPE) spheres, created by randomly removing particles from close-packed structures, revealed no velocity dependency in bouncing conditions, only a size dependency where larger aggregates are more prone to bouncing (Arakawa et al., 2023).
In this study, we performed N-body simulations using compressed aggregates derived from low-density aggregates to examine the potential dependence of bouncing conditions on the internal structure of aggregates. The aggregates were composed of 0.1 μm ice spheres, and we calculated the motion of the aggregates by solving the contact interaction of the constituent particles. The parameters included the filling factor, radius, and collision velocity of the aggregates. As a result, two trends dependent on collision velocity were identified for the bouncing conditions. For lower collision velocities, bouncing conditions consistent with experiments, showing a dependency on both mass and collision velocity, were obtained. When the collision velocity exceeds 10 m/s, the aggregates undergo plastic deformation and are confirmed to re-coagulate.
The results of this study indicate that the discrepancy in bouncing conditions between laboratory experiments and numerical simulations in previous simulations is due to differences in the internal structure of aggregates. CPE spheres used in previous studies have regions with locally high contact points throughout. High contact points are known to increase the likelihood of bouncing, which may have obscured the velocity dependency of bouncing conditions.
Additionally, using the obtained bouncing conditions, we also imposed size restrictions on high-density icy dust in protoplanetary disks. Although the dust size obtained in this study using is smaller than the dust sizes expected from observations, the formulation of the bouncing conditions suggests the potential to determine the physical properties of dust aggregates in the protoplanetary disk, such as the filling factor.
The bouncing behavior of dust aggregates has been studied through laboratory experiments and numerical simulations, resulting in differing bouncing conditions. Laboratory experiments using silicate spheres have shown that the effective mass of aggregates for bouncing is proportional to the collision velocity raised to the power of -4/3 (Kothe et al. 2013). In contrast, numerical simulations using close-packed and particle-extraction(CPE) spheres, created by randomly removing particles from close-packed structures, revealed no velocity dependency in bouncing conditions, only a size dependency where larger aggregates are more prone to bouncing (Arakawa et al., 2023).
In this study, we performed N-body simulations using compressed aggregates derived from low-density aggregates to examine the potential dependence of bouncing conditions on the internal structure of aggregates. The aggregates were composed of 0.1 μm ice spheres, and we calculated the motion of the aggregates by solving the contact interaction of the constituent particles. The parameters included the filling factor, radius, and collision velocity of the aggregates. As a result, two trends dependent on collision velocity were identified for the bouncing conditions. For lower collision velocities, bouncing conditions consistent with experiments, showing a dependency on both mass and collision velocity, were obtained. When the collision velocity exceeds 10 m/s, the aggregates undergo plastic deformation and are confirmed to re-coagulate.
The results of this study indicate that the discrepancy in bouncing conditions between laboratory experiments and numerical simulations in previous simulations is due to differences in the internal structure of aggregates. CPE spheres used in previous studies have regions with locally high contact points throughout. High contact points are known to increase the likelihood of bouncing, which may have obscured the velocity dependency of bouncing conditions.
Additionally, using the obtained bouncing conditions, we also imposed size restrictions on high-density icy dust in protoplanetary disks. Although the dust size obtained in this study using is smaller than the dust sizes expected from observations, the formulation of the bouncing conditions suggests the potential to determine the physical properties of dust aggregates in the protoplanetary disk, such as the filling factor.