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

¹ University of Duisburg-Essen, Faculty of Physics, Lotharstr. 1, 47057, Germany
e-mail: tabea.bogdan@uni-due.de
² University of Duisburg-Essen, Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), Lotharstr. 1, 47057 Duisburg, Germany

Received: 8 April 2020
Accepted: 30 April 2020

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 γ_e = 0.07 J m⁻². This value is dominated by abundant iron-oxides as measured by Mössbauer spectroscopy. Up to 1250 K, γ_e continuously decreases by up to a factor five. Olivines dominate at higher temperature. Beyond 1300 K dust grains significantly grow in size. The γ_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.