[P-PS06] Planetary Sciences

[PPS06-P22] Size-dependence of the merging criteria for planetesimal collision

Sota Nakahara¹, *Keiji Ohtsuki¹, Keisuke Sugiura², Hidenori Genda³, Kenji Kurosaki¹, Ryo Suetsugu⁴ (1.Graduate School of Science, Kobe University, 2.Advanced Technology R&D Center, Mitsubishi Electric Corporation, 3.Earth-Life Science Institute, Institute of Science Tokyo, 4.National Institute of Technology, Oshima College)

Keywords:Planet formation, Impact, Numerical simulation

When two planetesimals of similar masses undergo oblique impact at sufficiently high velocity, they would separate after the impact keeping their masses nearly unchanged. This is called hit-and-run impact. Clarifying the conditions for an impact lead to merging rather than hit-and-run is important for understanding the planetary accretion process. Previous studies on this issue have derived the transitional impact velocity between merging and hit-and-run by performing impact simulation with various mass ratios, total masses, impact angles, and impact velocities, etc. However, these studies have treated the objects as self-gravitating fluids, and have not investigated the merging criteria with the effects of disruption of rocks and friction among their fragments.

In this study, we performed simulations of impact between two equal mass planetesimals using the SPH code developed by Sugiura, Kobayashi, Inutsuka (2018), which can handle disruption of rocks and friction among their fragments, and investigated their merging criteria. We found that the effect of friction can facilitate merging for small planetesimals. Previous studies showed that the transition velocity normalized by the escape velocity does not depend on the size of the objects when the objects are treated as self-gravitating fluid, but we found that the value of the transition velocity normalized by the escape velocity changes depending on the size of the objects when friction between particles is taken into account. This is due to the fact that the pressures at impact differ depending on the size of the colliding objects, which in turn changes the frictional stress at impact. These effects may be important in the accretion process of small planetesimals.