Ice Grain Collisions in Comparison: CO$_2$, H$_2$O and their Mixtures

TL;DR

This study compares collision behaviors of CO₂, H₂O, and their mixtures at 80K, revealing that increasing water content enhances sticking efficiency, which is crucial for planetesimal formation.

Contribution

It provides experimental quantification of collision thresholds for CO₂, H₂O, and their mixtures, highlighting water's role in early planetary growth.

Findings

Higher water content increases the threshold velocity for sticking.

CO₂ ice behaves like silicates in collisions.

Water ice favors early planetesimal growth.

Abstract

Collisions of ice particles play an important role in the formation of planetesimals and comets. In recent work we showed, that CO$_2$ ice behaves like silicates in collisions. The resulting assumption was that it should therefore stick less efficiently than H$_2$O ice. Within this paper a quantification of the latter is presented. We used the same experimental setup to study collisions of pure CO$_2$ ice, pure water ice and 50\% mixtures by mass between CO$_2$ and water at 80K, 1 mbar and an average particle size of $\sim 90 \mu$m. The results show a strong increase of the threshold velocity between sticking and bouncing with increasing water content. This supports the idea that water ice is favorable for early growth phases of planets in a zone within the H$_2$O and the CO$_2$ iceline.