Photophoresis on water-ice particles induced by thermal radiation in protoplanetary discs

Abstract

It is widely believed that planets form in accretion discs by the growth of small dust and ice grains. To verify the scenarios of protoplanetary disc processes including the transport of material in vertical as well as in radial direction, it is crucial to understand the interaction of small dust and ice particles with their surroundings, i.e., with the gas, star light, and other ice and dust particles. In first laboratory experiments, we observe trapped irregular-shaped water-ice particles which levitate up to half an hour in a vacuum chamber at a pressure of about 2 mbar due to photophoresis and thermophoresis. While they are firmly levitating, they rotate preferentially about their vertical axis. The physics leading to the levitation is explained and the results of an analysis of the particle rotation are presented.