Collisional Growth and Fragmentation of Dust Aggregates. II. Mass Distribution of Icy Fragments

TL;DR

This study uses N-body simulations to analyze the mass distribution of icy dust fragments resulting from collisions, deriving analytic formulas and revealing how fragment size and mass transfer depend on collision parameters.

Contribution

It provides new analytic expressions for the mass distribution of fragments and insights into the dependence of fragmentation outcomes on collision velocity and mass ratio.

Findings

Power-law index of small fragments' mass distribution is independent of mass ratio.

Mass fraction of individual dust monomers decreases with increasing total mass of colliding aggregates.

Total geometric cross section of fragments is comparable to that of the target.

Abstract

By performing $N$-body simulations, we investigated fundamental processes of collisions between dust aggregates composed of submicron-sized icy dust monomers. We examined the mass distribution of fragments in the collisional outcomes in a wide range of the mass ratio and the collision velocity between colliding dust aggregates. We derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a large target to a small projectile, which occurs for a mass ratio of $\gtrsim 3$ and is shown in a previous study (Hasegawa et al. 2021). We found that the power-law index of the cumulative mass distribution of the small fragments is independent of the mass ratio and only weakly dependent on the collision velocity. On the other hand, the mass fraction of fragments of individual dust monomers decreases with an increasing total mass of colliding aggregates for a fixed mass ratio. This tendency implies that multiple hierarchical disruptive collisions (i.e., collisions between fragments, collisions between fragments of fragments) are required for producing a large amount of individual dust monomers via collisional fragmentation. Our fragment model suggests that the total geometric cross section integrated over the fragments is estimated to be about the same order of the geometric cross section of the target.