Composition and Sticking of Hot Chondritic Dust in a Protoplanetary Hydrogen Atmosphere

Abstract

Abstract The sticking properties of dust in early phases of planet formation depend on the thermal history and ambient atmosphere. Therefore, dust will change its ability to build larger aggregates in collisions, depending on its location in protoplanetary disks. We aim at quantifying the change in sticking properties as chondritic dust is heated under various atmospheric conditions. In laboratory experiments, we milled two different meteorites (Sayh al Uhaymir 001 and Allende) to dust and formed millimeter-size cylinders. These cylindrical aggregates were sequentially heated from 600 to 1400 K in vacuum and in a hydrogen atmosphere, with compositional changes being tracked via Mössbauer spectroscopy. Using a Brazilian splitting test, the splitting tensile strength was determined. At higher temperatures, iron in silicates is reduced to metallic Fe(Ni) within the hydrogen atmosphere. In any case, adhesive forces are strongly increased by orders of magnitude from 1000 to 1400 K with minimum variations, depending on the atmospheric conditions. The dust in protoplanetary disks becomes ever more sticky, approaching a sublimation line upon exposure to temperatures of about 1400 K.