Drifting inwards in protoplanetary discs I Sticking of chondritic dust at increasing temperatures

TL;DR

This study investigates how the sticking properties of chondritic dust in protoplanetary discs change with temperature, revealing decreased stability and growth potential of dust aggregates as they approach warmer inner regions.

Contribution

It provides experimental measurements of dust aggregate strength at high temperatures, highlighting the impact of temperature on dust growth and planetesimal formation in protoplanetary discs.

Findings

Effective surface energy decreases by up to a factor of five up to 1250 K.

Dust grains grow significantly beyond 1300 K, restricting aggregate formation.

Aggregation becomes impossible beyond 1400 K.

Abstract

Sticking properties rule the early phases of pebble growth in protoplanetary discs in which grains regularly travel from cold, water-rich regions to the warm inner part. This drift affects composition, grain size, morphology, and water content as grains experience ever higher temperatures. In this study we tempered chondritic dust under vacuum up to 1400 K. Afterwards, we measured the splitting tensile strength of millimetre-sized dust aggregates. The deduced effective surface energy starts out as $\gamma_e = 0.07\,\rm J/m^2$. This value is dominated by abundant iron-oxides as measured by M\"ossbauer spectroscopy. Up to 1250 K, $\gamma_e$ continuously decreases by up to a factor five. Olivines dominate at higher temperature. Beyond 1300 K dust grains significantly grow in size. The $\gamma_e$ no longer decreases but the large grain size restricts the capability of growing aggregates. Beyond 1400 K aggregation is no longer possible. Overall, under the conditions probed, the stability of dust pebbles would decrease towards the star. In view of a minimum aggregate size required to trigger drag instabilities it becomes increasingly harder to seed planetesimal formation closer to a star.