Research
Material Strength of Dust Aggregates Investigated by Numerical Simulations
The first step of planet formation is the accumulation of micron-sized dust grains. Once they become kilometer-sized, they are called planetesimals, whose formation process remains unknown. To unravel it, observations and explorations of comets and asteroids in our solar system, which are considered to be remnants of planetesimals, have been conducted (e.g., Rosetta and Hayabusa2). To unravel the formation process of planetesimals by using these exploration results, we have investigated and modeled the properties of dust aggregates using numerical simulations.
Tensile Strength
Explorations of our solar system have revealed the physical properties, such as tensile strength, of comets and asteroids.
In this paper, we calculated and modeled the tensile strength of dust aggregates in the intermediate stages of planetesimal formation
using numerical simulations.
Comparison with the tensile strength of Comet Churyumov-Gerasimenko (67P), which has been estimated by exploration,
shows that the comet is much more fragile than dust aggregates.
We succeeded in limiting the properties of the constituent grains needed to achieve the comet's fragility.
Tatsuuma et al. 2019, ApJ, 874, 159
Furthermore, using the tensile strength model of dust aggregates, we proposed a new disruption mechanism for dust aggregates in protoplanetary disks.
Dust aggregates rotate on their own axis like a pinwheel due to the gas flow they receive in protoplanetary disks.
By comparing the centrifugal force and the tensile strength of dust aggregates, it can be determined whether dust aggregates will be disrupted or not.
As a result, we succeeded in obtaining the conditions under which the disruption of dust aggregates due to their spinning motion affects the planetesimal formation.
Tatsuuma & Kataoka 2021, ApJ, 913, 132
Compressive Strength
The internal structure of these bodies, such as comets and asteroids, is determined by the balance between the strength of their constituting materials
and the self-gravity of the bodies.
In this paper, to investigate the formation process of planetesimals based on the physical properties of comets and asteroids,
we calculated and formulated the compressive strength of dust aggregates in the intermediate stages of planetesimal formation through numerical simulations.
As a result, we found that incorporating an excluded volume, a non-compressible volume that accounts for the volume of the constituent particles
and the void volume at the closest packing, significantly enhances the accuracy of reproducing the numerical simulation results.
Tatsuuma et al. 2023, ApJ, 953, 6
Furthermore, using a compressive strength model of dust aggregates, we modeled the bulk density of kilometer-sized dust aggregates.
The results showed that low-density trans-Neptunian objects (TNOs) and main belt asteroids (MBAs) can be explained as dust aggregates.
However, most TNOs, MBAs, comets, and near-Earth asteroids (e.g., Itokawa and Ryugu) have higher densities than the dust aggregate model predicts.
This suggests additional compression processes beyond self-gravity or formation from larger parent bodies.
Based on these findings, we proposed a new planetesimal formation scenario where compact dust aggregates observed in protoplanetary disks may be fragments of planetesimals.
Tatsuuma et al. 2024, ApJ, 974, 9