[M-GI30] Computational sciences on the universe, galaxies, stars, planets, and their environments

[MGI30-04] Particle number dependence of the internal structure of the Moon-forming disk

Takeru Yamaoka¹, *Takayuki Saitoh¹, Natsuki Hosono¹, Junichiro Makino¹ (1.Kobe university)

Keywords:Moon-forming disk, N-body simulation

The current concordance scenario for the formation of the Moon is that first, there was a giant impact, and then the Moon-forming disk was formed around the Earth. In the disk, small materials gravitationally aggregated to form the Moon. Since the Moon-forming disk was formed by the radiative cooling of gas, it would consist of very small rocky particles. Since the current computational resources are insufficient to represent all the small rocky particles, the resolution dependence of the numerical modeling of the Moon-forming disk is crucial. Sasaki & Hosono (2018) studied the resolution dependence of the evolution of the Moon-forming disk using up to 10⁷ particles, which is 2-3 orders of magnitude larger simulations than the previous studies. Here, we performed N-body simulations of the Moon-forming disk with up to 10⁷ particles to investigate further details of its dynamical evolution. We found that in the inner region of 1.6 R_earth the disk has the ring like structure, which is different from the well-known spiral structure. When we looked closely, it turned out that this ring-like structure is a very tightly wound leading spiral. This structure can be clearly seen in simulations with 10^6-7 particles, but it is hard to see in simulations with <= 10⁵ particles. This would be the reason why the previous studies did not point out the emergence of this structure. In studies on the Saturn's ring, it has been pointed out that the viscous overstability plays a crucial role to make the B ring become a steady state. Comparing our results with the local simulations of the B-ring, we found that the ring-spiral transition region of the Moon-forming disk is well matched with the B ring case. In addition, the ring separation distance normalized by the Toomre's critical wavelength is consistent with both our results and the B-ring. We also found that the angular momentum transfer to the outer region is inefficient with a larger number of simulations, which implies that further higher resolution studies are essential to confirm the convergence of the numerical modeling and to understand the detailed evolution of the Moon-forming disk.