Onset of planet formation in the warm inner disk -- Colliding dust aggregates at high temperatures

TL;DR

This study demonstrates that silicate dust aggregates in protoplanetary disks exhibit increased sticking probabilities at temperatures above 900 K, potentially influencing planetesimal formation processes.

Contribution

First laboratory collision experiments with hot levitated basalt dust aggregates across a range of high temperatures relevant for inner protoplanetary disks.

Findings

Sticking probability increases above 900 K

Dust growth is enhanced at high temperatures

Implications for planetesimal formation scenarios

Abstract

Collisional growth of dust occurs in all regions of protoplanetary disks with certain materials dominating between various condensation lines. The sticking properties of the prevalent dust species depend on the specific temperatures. The inner disk is the realm of silicates spanning a wide range of temperatures from room temperature up to sublimation beyond $1500\,\mathrm{K}$. For the first time, we carried out laboratory collision experiments with hot levitated basalt dust aggregates of $1\, \rm mm$ in size. The aggregates are compact with a filling factor of $0.37 \pm 0.06$. The constituent grains have a wide size distribution that peaks at about $0.6\,\mu \mathrm{m}$. Temperatures in the experiments are varied between approximately $600\,\mathrm{K}$ and $1100\,\mathrm{K}$. Collisions are slow with velocities between $0.002\,\mathrm{m}\,\mathrm{s}^{-1}$ and $0.15\,\mathrm{m}\,\mathrm{s}^{-1}$, i.e., relevant for protoplanetary disks. Aside from variations of the coefficients of restitution due to varying collision velocities, the experiments show low sticking probability below $900\,\mathrm{K}$ and an increasing sticking probability starting at $900\,\mathrm{K}$. This implies that dust can grow to larger size in hot regions, which might change planet formation. One scenario is an enhanced probability for local planetesimal formation. Another scenario is a reduction of planetesimal formation as larger grains are more readily removed as a consequence of radial drift. However, the increased growth at high temperatures likely changes planetesimal formation one way or the other.