Modeling the Contact Surfaces Formed by Pebble Collisions: Application to Formation of Comet 67P/Churyumov--Gerasimenko

TL;DR

This paper develops a model to analyze contact surfaces from pebble collisions, providing insights into comet 67P's formation, and estimates pebble sizes based on collision velocities and material properties.

Contribution

The paper introduces a new model linking collision velocity to contact surface and contact points, applied to comet formation scenarios, incorporating numerical simulations and material strength data.

Findings

Comet 67P likely formed via low-velocity pebble collisions below 10 cm/s.

Estimated pebble radius inside comet 67P is 130 micrometers or smaller.

Inelastic bouncing collisions helped damp collision velocities during formation.

Abstract

Modeling the contact surfaces formed by pebble collisions is crucial to understanding the formation process of comets, which are thought to be composed of pebbles. In this paper, we develop a new model to estimate the contact surface radius and the number of contact points as functions of collision velocity, and examine the formation process of comet 67P/Churyumov--Gerasimenko. Our model is based on the compressive strength of dust aggregates obtained from numerical simulations and assumes that all the impact energy of the pebbles is used for their mutual compression. We compare our model with numerical simulations of pebble collisions, in which we prepare the initial pebbles in the form of compressed dust aggregate spheres and measure the contact surface and pebble radii using two- and three-dimensional characteristic radii, respectively. We also apply our model to the formation scenario of comet 67P, whose tensile strength and bulk density have already been estimated in the literature. We find that its low tensile strength points to formation via pebble collisions at velocities below $\sim10\mathrm{\ cm\ s^{-1}}$ when a microscopic filling factor of pebbles is lower than 0.6, suggesting that inelastic bouncing collisions played a role in damping the collision velocities. By assuming that the pebble collision velocity is determined by the transition velocity between bouncing and sticking, we estimate the pebble radius inside comet 67P to be 130 $\mathrm{\mu m}$ or smaller.