Growth of Aggregates with Liquid-Like Ice-Shells in Protoplanetary Discs

TL;DR

This study investigates how liquid-like ice shells on dust aggregates in protoplanetary discs can enhance sticking during collisions, potentially enabling growth to centimeter sizes despite the bouncing barrier.

Contribution

It introduces a numerical analysis of collisions involving dust aggregates coated with liquid-like ice shells, highlighting their role in overcoming the bouncing barrier in planet formation.

Findings

Liquid-like ice shells increase sticking velocities.

A few microns of ice shell can enable growth to cm-sized clusters.

Simulation results support ice shells aiding planetesimal formation.

Abstract

During the first stages of planet formation, the collision growth of dust aggregates in protoplanetary discs (PPDs) is interrupted at the bouncing barrier. Dust aggregates coated by different species of ice turn out to be helpful to shift the bouncing barrier towards larger sizes due to their enhanced sticking properties in some cases. A rarely noticed fact is that H$_2$O- and H$_2$O-CH$_3$OH-NH$_3$-ice behave liquid-like when UV-irradiated within a PPD-similar environment. Dust aggregates coated by these ice species might be damped in collisions due to the liquid-like ice-shell which would effectively results in an increase of the sticking velocity. In this work, collisions of dust aggregates covered by the liquid-like H$_2$O-CH$_3$OH-NH$_3$-ice-shell are considered numerically. The coefficient of restitution and the sticking velocity are calculated for different thicknesses of the ice-shell. The simulation predicts that an ice-shell-thickness of few microns would be sufficient to allow the growth of cm-sized clusters in the PPD.