[P-PS07] Formation and evolution of planetary materials in the Solar System

[PPS07-21] Chondrule Formation via Debris Dust Bombardment on Planetesimals

*Sota Arakawa¹, Hidekazu Tanaka², Takayuki Ushikubo¹, Makiko Nagasawa³, Toshihiko Kadono⁴, Hiroshi Kobayashi⁵ (1.Japan Agency for Marine-Earth Science and Technology, 2.Tohoku University, 3.Kurume University, 4.University of Occupational and Environmental Health, 5.Nagoya University)

Keywords:Chondrule

Chondrules are the primary components of chondrites, and understanding the mechanisms of their formation and accumulation is essential for elucidating the history of planet formation in the solar system. Many chondrule formation mechanisms have been proposed to date, but it still remains challenging to simultaneously satisfy various constraints such as the abundance, formation timing, and material characteristics of chondrules. In particular, the bow shock heating model induced by planetesimals with high orbital eccentricities (e.g., Weidenschilling et al. 1998), which has been regarded as the leading hypothesis, is being questioned. This is because the gas density in the protosolar disk would have decreased significantly after Jupiter's formation (Tanigawa & Tanaka 2016; Tanaka et al. 2020), making it difficult to sufficiently heat the precursors of chondrules.
Here, we propose a new mechanism for chondrule formation: debris dust bombardment on planetesimals. After Jupiter formed in the protosolar disk, the region inside Jupiter's orbit became depleted of gas, leading to the formation of a geometrically thin debris dust layer. In addition, the eccentricities of planetesimals in the vicinity of the asteroid belt increased due to mean-motion resonances with Jupiter (Nagasawa et al. 2019), creating a situation where debris dust collides with planetesimals at high velocities of several km/s. When planetesimals enter the dust layer at high speeds, significant amounts of molten silicate droplets are produced around them. These droplets cool and solidify to form chondrules, which are then deposited into the dust layer. We estimate the heating efficiency of the dust layer and the production rate of chondrules using analytic calculations. Our results suggest that the entire dust layer could be heated within a million years, with the majority of the original debris dust being converted into chondrules.